DIZZINESS, VERTIGO, AND HEARING LOSS

Transcription

1 C H A P T E R 18 DIZZINESS, VERTIGO, AND HEARING LOSS Kevin A. Kerber and Robert W. Baloh General Considerations 237 Historical Background 237 Epidemiology of Vertigo, Dizziness, and Hearing Loss Normal Anatomy And Physiology 238 Approach to the Patient with Dizziness 240 History of Present Illness 240 Physical Examination 241 General Medical Examination 241 General Neurological Examination 241 The Neurotological Examination 242 Dizziness and Vertigo 245 Specific Disorders Causing Vertigo 245 Peripheral Vestibular Disorders 245 Central Nervous System Disorders 246 Vertigo in Inherited Disorders 247 Common Causes of Nonspecific Dizziness 249 Common Presentations of Vertigo 249 Acute Severe Vertigo 249 Recurrent Attacks of Vertigo 249 Recurrent Positional Vertigo 249 Hearing Loss 250 Classification of Hearing Loss 250 Conductive Hearing Loss 250 Sensorineural Hearing Loss 250 Central Hearing Loss Dizziness is a term patients use to describe a variety of symptoms including spinning or movement of the environment (vertigo), lightheadedness, presyncope, or imbalance. Patients also may use the term for other sensations such as visual distortion, internal spinning, nonspecific disorientation, and anxiety, so the most important initial step is to clarify the symptom. For the neurologist evaluating patients with dizziness, peripheral vestibular disorders are important to recognize because they are common and definable at the bedside and often are missed by referring physicians. Patients may experience dizziness in isolation or with other symptoms. Neurological causes should be considered when other neurological signs and symptoms are present and when common peripheral vestibular disorders have been ruled out. It is critical to ask the patient about associated symptoms because they may be the key to the diagnosis. Vertigo, a sensation of spinning of the environment, indicates a lesion within the vestibular pathways, either peripheral or central. Associated ear symptoms such as hearing loss and tinnitus can suggest a peripheral localization, to the inner ear or eighth nerve. Many Specific Disorders Causing Hearing Loss 250 Ménière s Disease 250 Cerebellopontine Angle Tumors 251 Superior Canal Dehiscence 251 Otosclerosis 251 Noise-Induced Hearing Loss 251 Genetic Disorders 251 Ototoxicity 251 Common Presentations of Hearing Loss 251 Asymmetrical Sensorineural Hearing Loss Sudden Sensorineural Hearing Loss 251 Hearing Loss with Age 252 Tinnitus 252 Clinical Investigations 252 Dizziness and Vertigo 252 General Tests 252 Imaging 252 Vestibular Testing 252 Auditory Testing 253 Hearing Loss and Tinnitus different types of hearing loss occur with or without dizziness, and an understanding of common auditory disorders is important to the practicing neurologist. With an understanding of the neurotological bedside examination, specific findings often can be identified. This chapter provides background information regarding dizziness, vertigo, and hearing loss and the clinical information necessary for making specific diagnoses. Further details on testing and management of these patients are presented in Chapter 40. GENERAL CONSIDERATIONS HISTORICAL BACKGROUND Accounts of dizziness and vertigo can be found in the writings of ancient Egyptian and Greek physicians. Before the late 19th century, however, not much was known about the causes 237 Ch18-H7525.indd /24/07 2:46:38 PM

2 238 P ART 1 Approach to Common Neurological Problems of dizziness or hearing loss; as a result, quackery was commonplace. Patients complaining of dizziness or vertigo usually were grouped together with those who had experienced epileptic seizures or stroke, under the rubric of apoplectiform cerebral congestion, meaning too much blood to the brain. Accordingly, common treatments included bleeding, leeching, cupping, and purging. In 1861, Prosper Ménière was the first to recognize the association of vertigo with hearing loss and thus to localize the symptom to the inner ear (Baloh, 2001). Although not well received initially, his discovery provided the basis for later studies on the physiology and pathology of the vestibular system. Caloric testing, the most widely used test of the vestibuloocular reflex (VOR), was introduced by Robert Barany in He later was awarded the Nobel Prize for proposing the mechanism of caloric stimulation. Barany also provided the first clinical description of benign paroxysmal positional vertigo (BPPV) in Endolymphatic hydrops was identified in postmortem specimens of patients with Ménière s disease in A method for measuring eye movements in response to caloric and rotational stimuli (electronystagmography [ENG]) was introduced in the 1930s, but it was not until the 1970s that digital computers were used to quantify eye movement responses. The advent of modern neuroimaging in the late 1970s and 1980s greatly expanded our understanding of causes of dizziness and vertigo. Before this time, stroke was considered an exceedingly rare cause of recurrent vertigo. Although the role of stroke in the pathogenesis of vertigo remains a controversial topic even today, infarctions within the cerebellum and brainstem have been identified on imaging studies in patients with isolated vertigo. Such studies continue to lead to new discoveries of causes of vertigo, as demonstrated by the recently described disorder of superior canal dehiscence. Unfortunately, the most common causes of vertigo, such as Ménière s disease, benign paroxysmal positional vertigo, and vestibular neuritis, still have no identifiable imaging characteristics. Over the past two decades, our understanding of the mechanisms for the common neurotological disorders has been enhanced. BPPV can now be readily identified and cured at the bedside with simple positional maneuvers (Aw et al., 2005; von Brevern et al., 2006). The head-thrust test can be used at the bedside to confirm a vestibular nerve lesion (Nuti et al., 2005). This sign is analogous to the afferent pupillary defect, which is the definitive diagnostic sign for localizing lesions to the optic nerve. Controversies regarding Ménière s disease have been clarified, and medical and surgical treatments have improved (Minor et al., 2004). We now know that patients with recurrent episodes of vertigo without hearing loss, a condition once called vestibular Ménière s disease, do not have Ménière s disease. Migraine is now recognized as an important cause of dizziness, even in patients without simultaneous headaches. In fact, benign recurrent vertigo (recurrent episodes of vertigo without accompanying auditory symptoms or other neurological features) usually is a migraine equivalent (Oh et al., 2001a). The disorder of superior canal dehiscence was only recently described and provides important insight into the physiology of the vestibular system (Minor, 2005). A more detailed description of the rotational vertebral artery syndrome has led to the appreciation of the high metabolic demands of the inner ear and its susceptibility to ischemia (Choi et al., 2005). Genetic research has identified ion channel dysfunction in disorders such as episodic ataxia and familial hemiplegic migraine, two disorders commonly associated with vertigo (Jen et al., 2004a). Identification of specific genes causing vertigo syndromes should lead to a better understanding of the mechanisms and also will create the opportunity to develop specific treatments in the future. EPIDEMIOLOGY OF VERTIGO, DIZZINESS, AND HEARING LOSS A recent population-based telephone survey in Germany showed that nearly 30% of the population has experienced moderate to severe dizziness (Neuhauser et al., 2005). Although most affected persons reported nonspecific forms of dizziness, nearly a quarter had true vertigo. Dizziness is more common among females and older people and has important health care utilization implications, because up to 80% of patients with dizziness seek medical care at some point. In the United States, the National Centers for Health Statistics reports 7.5 million annual ambulatory visits to physician offices, hospital outpatient departments, and emergency departments for dizziness, making it one of the most common principal complaints (Burt and Schappert, 2004). Prevalence rates for specific types of dizziness, however, are not available outside of tertiary referral centers or small studies. Hearing loss is an important cause of disability and affects approximately 16% of adults (older than 18 years of age) in the United States (Lethbridge-Cejku et al., 2006). Men are more commonly affected than women, and prevalence increases dramatically with age, so that by age 75, nearly 50% of the population report hearing loss. The most common type of hearing loss is sensorineural, and both idiopathic presbycusis and noiseinduced forms are common etiologic disorders. Tinnitus is less frequent in the U.S. population, with approximately 3% reporting it, although this rate increases to approximately 9% for persons older than 65 (Adams et al., 1999). Among persons with hearing loss, nearly 75% also experience tinnitus. The most common type of tinnitus is a high-pitched ringing in both ears. NORMAL ANATOMY AND PHYSIOLOGY The inner ear is composed of a fluid filled sac enclosed by a bony capsule with an anterior cochlear part, a central chamber (the vestibule), and a posterior vestibular part (Fig. 18-1). Endolymph fills up the fluid-filled sac and is separated by a membrane from the perilymph. These fluids differ primarily in their composition of potassium and sodium, with the endolymph resembling intracellular fluid, with a high potassium and low sodium content, and the perilymph resembling extracellular fluids, with a low potassium and high sodium content. Perilymph communicates with the cerebrospinal fluid through the cochlear aqueduct. The cochlea senses sound waves after they travel through the external auditory canal and are amplified by the tympanic membrane and ossicles of the middle ear (Baloh and Honrubia, 2001). The stapes, the last of three ossicles in the middle ear, contacts the oval window, which directs the forces associated with sound waves along the basilar membrane of the cochlea. These forces stimulate the hair cells, which in turn generate neural signals in the auditory nerve. The auditory nerve enters the lateral brainstem at the pontomedullary junction and Ch18-H7525.indd /24/07 2:46:39 PM

3 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 239 Cerebrospinal fluid K + = 4 meq/liter Na + = 152 meq/liter Protein = mg/dl Endolymphatic sac Figure 18-1 Anatomy of the inner ear. CSF, cerebrospinal fl uid. (From Baloh, R. W. 1998, Dizziness, Hearing Loss, and Tinnitus, F. A. Davis, Philadelphia, Figure 6, p. 16.) CSF Dura mater Anterior canal Posterior canal Horizontal canal Cochlear aqueduct Endolymphatic duct Scala vestibuli Perilymph K + = 10 meq/liter Na + = 140 meq/liter Protein = mg/dl Cochlear duct Scala tympani Endolymph K + = 144 meq/liter Na + = 5 meq/liter Protein = 126 mg/dl Utricle Round window Ductus reuniens Saccule synapses in the cochlear nucleus. The trapezoid body is the major decussation of the auditory pathway, but many fibers do not cross to the contralateral side. Signals then travel to the superior olivary complex. Some projections travel from the superior olivary complex to the inferior colliculus through the lateral lemnisci, and others terminate in one of the nuclei of the lateral lemniscus. Next, the fibers travel to the ipsilateral medial geniculate body, and then auditory radiations pass through the posterior limb of the internal capsule to reach the auditory cortex of the temporal lobe. The peripheral vestibular system is composed of three semicircular canals, the utricle and saccule, and the vestibular component of the eighth cranial nerve (Baloh and Honrubia, 2001). Each semicircular canal has a sensory epithelium called the crista; the sensory epithelium of the utricle and saccule is called the macule. The semicircular canals sense angular movements, whereas the utricle and saccule sense linear movements. Two of the semicircular canals (anterior and posterior canals) are oriented in the vertical plane nearly orthogonal to each other; the third canal is oriented in the horizontal plane (horizontal canal). The crista of each canal is activated primarily by movement occurring in the plane of that canal. When the hair cells of these organs are stimulated, the signal is transferred to the vestibular nuclei via the vestibular portion of the eighth cranial nerve. Signals originating from the horizontal semicircular canal then pass via the medial longitudinal fasciculus along the floor of the fourth ventricle to the abducens nuclei in the middle brainstem and the oculomotor complex in the rostral brainstem. The anterior (also referred to as the superior) and posterior canal impulses pass from the vestibular nuclei to the ocular motor and trochlear nuclei, triggering eye movements roughly in the plane of each canal. A key feature is that once vestibular signals leave the vestibular nuclei, they divide into vertical, horizontal, and torsional components. As a result, a lesion of central vestibular pathways can cause a pure vertical, pure torsional, or pure horizontal nystagmus. The primary vestibular afferent nerve fibers maintain a constant baseline firing rate of action potentials. When the baseline rate from each ear is symmetrical (or an asymmetry has been centrally compensated), the eyes remain stationary. With an uncompensated asymmetry in the firing rate, resulting from either increased or decreased activity on one side, slow ocular deviation results. By turning the head to the right, the baseline firing rate of the horizontal canal is physiologically altered, causing an increased firing rate on the right side and a decreased firing rate on the left side (Fig. 18-2). The result is a slow deviation of the eyes to the left. In an alert person, this slow deviation is regularly interrupted by quick movements in the opposite direction (nystagmus) so that the eyes do not become pinned to one side. In a comatose patient, the eyes deviate to the side of the slow component because the corrective fast phases are truncated or absent. The plane in which the eyes deviate as a result of vestibular stimulation depends on the combination of canals that are stimulated (Table 18-1). If only the posterior semicircular canal on one side is stimulated (as occurs with benign Ch18-H7525.indd /24/07 2:46:39 PM

4 240 P ART 1 Approach to Common Neurological Problems PC HC AC Ampulla Physiologic nystagmus Utricle Spontaneous nystagmus Figure 18-2 Primary afferent nerve activity associated with rotation-induced physiological nystagmus and spontaneous nystagmus resulting from a lesion of one labyrinth. The thin straight arrows indicate the direction of slow components; the thick straight arrows indicate the direction of fast components; curved arrows show the direction of endolymph fl ow in the horizontal semicircular canals. AC, anterior canal; HC, horizontal canal; PC, posterior canal. (From Baloh, R. W. 1998, Dizziness, Hearing Loss, and Tinnitus, F. A. Davis, Philadelphia, Figure 16, p. 36.) Primary afferent firing rate 100 msec Table 18-1 Physiological Properties and Clinical Features of the Components of the Peripheral Vestibular System TRIGGERED EYE COMMON CLINICAL LOCALIZATION COMPONENT(S) MOVEMENTS CONDITIONS LOCALIZING FEATURES SEMICIRCULAR CANALS Posterior canal PC Vertical, torsional BPPV-PC Nystagmus Anterior canal AC Vertical, torsional BPPV-AC, SCD Nystagmus, fi stula test Horizontal canal HC Horizontal >> torsional BPPV-HC, fi stula Nystagmus, fi stula test VESTIBULAR NERVE Superior division AC, HC, utricle Horizontal > torsional VN, ischemia Nystagmus, head thrust test Inferior division PC, saccule Vertical, torsional VN, ischemia Nystagmus Common trunk (cranial AC, HC, PC, Horizontal > torsional VN, VP, ischemia Nystagmus, head thrust test, nerve VIII) utricle, saccule auditory fi ndings LABYRINTH AC, HC, PC, utricle, Horizontal > torsional EH, labyrinthitis Nystagmus, auditory fi ndings saccule AC, anterior canal; BPPV, benign paroxysmal positional vertigo; EH, endolymphatic hydrops; HC, horizontal canal; PC, posterior canal; SCD, superior canal dehiscence; VN, vestibular neuritis; VP, vestibular paroxysmia. paroxysmal positional vertigo), a vertical-torsional deviation of the eyes can be observed, which is followed by a fast corrective response in the opposite direction. However, if the horizontal canal is the source of stimulation (as occurs with the horizontal canal variant of BPPV), a horizontal deviation with a slight torsional component (because this canal is slightly off the horizontal plane) results. If the vestibular nerve is lesioned (as in vestibular neuritis) or stimulated (as in vestibular paroxysmia), a horizontal greater than torsional nystagmus occurs, which is the vector sum of all three canals, because the two vertical canals on one side cancel each other out. Over time, either an asymmetry in the baseline firing rates resolves (the stimulation has been removed), or the central nervous system compensates for it. This explains why an entire unilateral peripheral vestibular system can be surgically destroyed and the patient experiences vertigo only for several days to weeks. It also explains why patients with slow-growing tumors affecting the vestibular nerve, such as an acoustic neuroma, generally do not experience vertigo or nystagmus. APPROACH TO THE PATIENT WITH DIZZINESS HISTORY OF PRESENT ILLNESS The history and physical examination provide the most important information in the evaluation of patients complaining of Ch18-H7525.indd /24/07 2:46:40 PM

5 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 241 dizziness (Colledge et al., 1996; Lawson et al., 1999). Often, patients have difficulty describing the exact symptom experienced, so the clinician must elicit the pertinent information. The first step is to define the symptom. No clinician should ever be satisfied to record the complaint simply as dizziness. If the patient is unable to provide a more detailed description of the symptom, the physician can ask the patient to place the symptom into one of the following categories: movement of the environment (vertigo), lightheadedness, or imbalance alone, without an abnormal head sensation. The physician also should ask the following questions: Is the symptom constant or episodic? Are there accompanying symptoms? How did it begin (e.g., gradual or sudden)? Were there aggravating or alleviating factors? With episodic dizziness, what are the duration and frequency of attacks? Are there identifiable triggers? Table 18-2 displays the key distinguishing features of common causes of dizziness. One key point is that any type of dizziness may worsen with position changes, but that some disorders such as BPPV occur only after position change. PHYSICAL EXAMINATION General Medical Examination A brief general medical examination is important. Identifying orthostatic blood pressure changes can be diagnostic in the correct clinical setting; therefore, blood pressure should be checked for this pattern in any patient with orthostatic symptoms. Orthostatic hypotension probably is the most common general medical cause of dizziness among patients referred to neurologists. Identifying an irregular heart rhythm also may be pertinent. Other general examination measures to consider in individual patients include a visual acuity assessment (adequate vision is important for balance) and a musculoskeletal inspection (significant arthritis can impair gait). General Neurological Examination The general neurological examination is an essential component of the evaluation of patients complaining of dizziness, Table 18-2 Distinguishing Among Common Peripheral and Central Vertigo Syndromes DURATION OF ASSOCIATED CAUSE HISTORY OF VERTIGO VERTIGO SYMPTOMS PHYSICAL EXAMINATION PERIPHERAL Vestibular neuritis Single prolonged episode Days to weeks Nausea, imbalance Peripheral nystagmus, positive head thrust test, imbalance Benign paroxysmal Positionally triggered <1 min Nausea Characteristic positionally positional vertigo episodes triggered burst of nystagmus Ménière s disease May be triggered by Hours Unilateral ear fullness, Unilateral low-frequency salty foods tinnitus, hearing loss, hearing loss nausea Vestibular Abrupt onset; spontaneous Seconds Tinnitus, hearing loss Usually normal paroxysmia or positionally triggered Perilymph fi stula Triggered by sound or Seconds Hearing loss, Nystagmus triggered by loud sounds pressure changes hyperacusis or pressure changes CENTRAL Stroke/TIA Abrupt onset; spontaneous Stroke, >24 hr; TIA, Brain-stem, cerebellar Spontaneous central nystagmus; usually minutes gaze-evoked nystagmus; usually focal neurologic signs Multiple sclerosis Subacute onset Minutes weeks Unilateral visual loss, Central types or rarely peripheral diplopia, types of spontaneous or positional incoordination, nystagmus; usually other focal ataxia neurologic signs Neurodegenerative May be spontaneous or Minutes hours Ataxia Central types of spontaneous or disorders positionally triggered positional nystagmus; gaze-evoked nystagmus; cerebellar, extrapyramidal and frontal signs Migraine Onset usually associated Seconds days Headache, visual aura, Normal interictal exam. with typical migraine photo-/phonophobia Ictal examination may show triggers peripheral or central types of spontaneous or positional nystagmus. Familial ataxia Acute-subacute onset; Hours Ataxia Central types of spontaneous syndromes usually triggered by or positional nystagmus; ictal, stress, exercise, or or even interictal, gaze-evoked excitement nystagmus; ataxia; gait disorders TIA, transient ischemic attack. Ch18-H7525.indd /24/07 2:46:40 PM

6 242 P ART 1 Approach to Common Neurological Problems because dizziness can be the earliest symptom of a neurodegenerative disorder (de Lau et al., 2006) and also can be an important symptom of stroke, tumor, demyelination, or other problems of the nervous system. Mental status usually can be inferred from the patient s ability to provide a history. The cranial nerves should be thoroughly inspected in patients complaining of dizziness. The most important part of the examination lies in the assessment of ocular motor function (described in more detail in the neurotology examination section). The examiner should determine whether the patient has full ocular movements. A posterior fossa mass can impair facial sensation and the corneal reflex on one side. Assessing facial strength and symmetry is important because of the close anatomical relationship between the seventh and the eighth cranial nerves. The lower cranial nerves also should be assessed by observing palatal elevation, tongue protrusion, and trapezius and sternocleidomastoid strength. Increased tone or cogwheel rigidity may be the main finding in a patient with an early neurodegenerative disorder. The peripheral sensory examination is important because a peripheral neuropathy can cause a nonspecific dizziness or imbalance. Reflexes should be tested for their presence and symmetry. Also to be taken into consideration are the normal decrease in vibratory sensation and the possibility of absence of ankle jerks in elderly patients. Coordination is an important part of the neurological examination in patients with dizziness because disorders characterized by ataxia can manifest with the principal symptom of dizziness. The finger-nose-finger test, the heel-knee-shin test, and rapid alternating movements assess extremity coordination. The Neurotological Examination The neurotological examination is a specialty examination expanding on certain aspects of the general neurological examination and also includes an audiovestibular assessment. Ocular Motor Function Testing The first step in assessing ocular motor function is to search for spontaneous involuntary movements of the eyes. The examiner asks the patient to look straight ahead while observing for nystagmus or saccadic intrusions. Nystagmus is characterized by a slow and fast phase component and is classified as spontaneous, gaze-evoked, or positional. The direction of nystagmus is described conventionally by the direction of the fast phase. Whether the nystagmus is vertical, horizontal, or torsional, or a mixture of these, provides important localizing information. Spontaneous nystagmus can have either a peripheral or a central pattern. As a general rule with only rare exception, central lesions can mimic a peripheral pattern of nystagmus (Lee and Cho, 2004), but peripheral lesions cannot cause central patterns of nystagmus. A peripheral pattern of spontaneous nystagmus is unidirectional; that is, the eyes beat only to one side (shown in Video 18-1, available at Peripheral spontaneous nystagmus never changes direction. It usually has a horizontal greater than torsional pattern because of the physiology of the asymmetry in firing rates within the peripheral vestibular system whereby the vertical canals cancel each other out. The prominent horizontal component results from the unopposed horizontal canal. Other characteristics of peripheral spontaneous nystagmus are suppression with visual fixation, increase in amplitude with gaze in the direction of the fast phase, and decrease with gaze in the direction opposite that of the fast phase. Some patients are able to suppress this nystagmus so well at the bedside, or have partially recovered from the initiating event, that spontaneous nystagmus may appear only by removing visual fixation. Several simple bedside techniques can be used to remove the patient s ability to fixate. Frenzel glasses are designed to remove visual fixation by using +30-diopter lenses. An ophthalmoscope can be used to block fixation. While the fundus of one eye is being viewed, the patient is asked to cover the other eye. Probably the simplest technique involves holding a blank sheet of paper close up to the patient s face (so as to block visual fixation ability) and observing for spontaneous nystagmus from the side. Saccadic intrusions are spontaneous, unwanted saccadic movements of the eyes that do not have the rhythmic fast and slow phases characteristic of nystagmus. Saccades (fast movements of the eyes normally under voluntary control) shift gaze from one object to another. Square wave jerks and saccadic oscillations are the most common types of saccadic intrusions. Square wave jerks are small-amplitude, involuntary saccades that take the eyes off a target, followed after a normal intersaccadic delay (around 200 ms) by a corrective saccade to bring the eyes back to the target. Square wave jerks can be seen in neurological disorders such as cerebellar ataxia, Huntington s disease, or progressive supranuclear palsy but also occur in normal persons (see Chapter 38). Saccadic oscillations are back-to-back saccadic movements and thus do not have the intersaccadic interval characteristic of square wave jerks. The appearance is thus of an oscillation. When a burst occurs only in the horizontal plane, the term ocular fl utter is used (as shown in Video 18-2, available at When vertical or torsional components are present, the term opsoclonus is used. The eyes make constant random conjugate saccades of unequal amplitude in all directions. Ocular flutter and opsoclonus are pathological findings typically encountered in several different types of central nervous system diseases involving brainstem-cerebellar pathways. Paraneoplastic disorders should be considered in patients presenting with ocular flutter or opsoclonus. Gaze Testing The patient should be asked to look to the left, right, up, and down; the examiner looks for gaze-evoked nystagmus in each position (demonstrated in Video 18-3, available at com). Occurrence of a few beats of nonsustained nystagmus with gaze greater than 30 degrees is called end-gaze nystagmus and is a variable finding in normal persons. Gaze-evoked downbeating nystagmus (shown in Video 18-4, available at www. nicp.com), vertical nystagmus that increases on lateral gaze, localizes to the craniocervical junction and midline cerebellum. Gaze testing also may trigger saccadic oscillations. Smooth Pursuit Smooth pursuit refers to the voluntary movement of the eyes used to track a target moving at a low velocity. It functions to keep the moving object on the fovea to maximize vision. Although characteristically a very smooth movement at low Ch18-H7525.indd /24/07 2:46:40 PM

7 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 243 velocity testing, smooth pursuit capability inevitably breaks down when tested at high velocities. Although smooth pursuit traditionally was thought to be highly variable in elderly subjects, a recent study found no significant decline in smooth pursuit capability in a group of healthy elderly persons (older than 75 years) tested yearly for at least 9 years (Kerber et al., 2006). Patients with impaired smooth pursuit require frequent small saccades to keep up with the target; accordingly, the term saccadic pursuit is used to describe this finding (see Video 18-3). Abnormalities of smooth pursuit occur as the result of disorders throughout the central nervous system and with use of tranquilizing medicines or alcohol and with fatigue. Patients with diffuse cortical disease, basal ganglia disease, or diffuse cerebellar disease consistently have bilaterally impaired smooth pursuit. Patients with early or mild cerebellar degenerative disorders may have markedly impaired smooth pursuit with mild or minimal truncal ataxia as the only findings. Saccades Saccades are fast eye movements (velocity of this eye movement can be as high as 600 degrees per second) used to quickly bring the image of an object onto the fovea. Saccades are generated by the burst neurons of the pons (horizontal movements) and the midbrain (vertical movements). Lesions or degeneration of these regions leads to slowing of saccades, which can also occur with lesions of the oculomotor neurons or extra ocular muscles. Severe slowing can be readily appreciated at the bedside by instructing the patient to look back and forth from one object to another. The examiner observes both the velocity of the saccade and the accuracy. Overshooting saccades missing the target and then needing to correct, termed ocular dysmetria indicates a lesion of the cerebellum (as seen in Video 18-5, available at Undershooting saccades are less specific and often occur in normal persons. Optokinetic Nystagmus and Fixation Suppression of the Vestibulo-ocular Reflex Optokinetic nystagmus (OKN) and fixation suppression of the vestibulo-ocular reflex (VOR suppression) also can be tested at the bedside. OKN is a combination of fast (saccadic) and slow (smooth pursuit) movements of eyes and can be observed in normal persons when they are watching a moving train, for example. OKN is maximally stimulated with both foveal and parafoveal stimulation; thus, the proper laboratory technique for measuring OKN utilizes a full-field stimulus by having the patient sit stationary while a large rotating pattern moves around the patient. This test can be approximated at the bedside by moving a striped cloth in front of the patient, although this technique stimulates only the fovea. Patients with disorders causing severe slowing of saccades will not be able to generate OKN, so their eyes will become pinned to one side. VOR suppression can be tested at the bedside using a swivel chair. The patient sits in the chair and extends his or her arm in the thumbs-up position out in front. The patient is instructed to focus on the thumb and to allow the extended arm to move with the body so that the visual target of the thumb remains directly in front of the patient. The chair is then rotated from side to side. The patient s eyes should remain locked on the thumb, demonstrating the ability to suppress the VOR stimulated by rotation of the chair. Nystagmus will be observed during the rotation movements in patients with impairment of VOR suppression, which is analogous to impairment of smooth pursuit. Vestibular Nerve Examination Although the vestibular nerve examination often is omitted as part of the cranial nerve examination in general neurology texts, important localizing information can be obtained about the functioning of the vestibular nerve at the bedside. A unilateral or bilateral vestibulopathy can be identified using the head thrust test (as shown in Video 18-6, available at com). To perform this test, the physician stands directly in front of the patient seated on the examining table. With the patient s head held in the examiner s hands, the patient is instructed to focus on the examiner s nose. The head is then quickly moved about 5 to 10 degrees to one side. In patients with normal vestibular function, the VOR results in movement of the eyes in the direction opposite the head movement. Therefore, the patient s eyes remain fixated on the examiner s nose after the sudden movement. The test is repeated in the opposite direction. If the examiner observes a corrective saccade bringing the patient s eyes back to the examiner s nose after the head thrust, impairment of the VOR in the direction of the head movement is identified. Rotating the head slowly back and forth (the doll s eye maneuver) also induces compensatory eye movements, but both the visual and vestibular systems are activated by this lowvelocity test, enabling a patient with vestibular function loss but normal visual pursuit to have normal-appearing compensatory eye movements. This slow rotation of the head, however, is helpful in a comatose patient, who is not able to generate voluntary visual tracking eye movements. Slowly rotating the head also can be a helpful test in patients with impairment of the smooth pursuit system because smooth movements of the eyes with slow rotation of the head indicate an intact VOR. Positional Testing Positional testing can help identify peripheral or central causes of vertigo. The most common positional vertigo, BPPV, is caused by free-floating calcium carbonate debris, usually in the posterior semicircular canal but occasionally in the horizontal canal or, rarely, the anterior canal. The characteristic burst of upbeat, torsional nystagmus is triggered in patients with BPPV by a rapid change from erect sitting to supine head-hanging left or head-hanging right the Dix-Hallpike test (as shown in Video 18-7, available at When present, the nystagmus usually is triggered in only one of these positions. A burst of nystagmus in the opposite direction (downbeat torsional) occurs when the patient resumes the sitting position. A repositioning maneuver can be used to liberate the clot of debris from the posterior canal. We use the modified Epley maneuver (Fig. 18-3) (as shown in Video 18-8, available at com), which is more than 80% effective in treating patients with posterior canal BPPV, compared with 10% effectiveness of a sham procedure (von Brevern et al., 2006). The key feature of this maneuver is the roll-across in the plane of the posterior canal so that the clot rotates around the posterior canal and out into the utricle. Once the clot enters the utricle, it may reattach to the membrane, dissolve, or even remain free-floating in the Ch18-H7525.indd /24/07 2:46:41 PM

8 244 P ART 1 Approach to Common Neurological Problems E D Utricle E D PSC C A A C B Figure 18-3 Treatment maneuver for benign paroxysmal positional vertigo affecting the right ear. The procedure can be reversed for treating the left ear. The drawing of the labyrinth in the center shows the position of the debris as it moves around the posterior semicircular canal (PSC) and into the utricle (UT). A, The patient is seated upright, with head facing the examiner, who is standing on the right. B, The patient is then rapidly moved to head-hanging right position (Dix-Hallpike test). This position is maintained until the nystagmus ceases. The examiner moves to the head of the table, repositioning hands as shown. C, The head is rotated quickly to the left with right ear upward. This position is maintained for 30 seconds. D, The patient rolls onto the left side while the examiner rapidly rotates the head leftward until the nose is directed toward the fl oor. This position is then held for 30 seconds. E, The patient is rapidly lifted into the sitting position, now facing left. The entire sequence should be repeated until no nystagmus can be elicited. After the maneuver, the patient is instructed to avoid head hanging positions to prevent the debris from reentering the posterior canal. (From Rakel, E. (Ed.). 1995, Conn s Current Therapy, WB Saunders, Philadelphia.) utricle, but the debris no longer disrupts semicircular canal function. Recurrences, however, are common. If the debris is in the horizontal canal, positionally triggered direction-changing horizontal nystagmus is seen. Patients are tested for the horizontal canal variant of BPPV by turning the head to each side while lying in the supine position. The nystagmus can be either paroxysmal geotropic (beating toward the ground) or persistent apogeotropic (beating away from the ground) nystagmus. The side with the stronger nystagmus is the side with the debris in the horizontal canal. The debris can be removed from the canal by rolling the patient (barbecue fashion) toward the normal side. Positional testing also can trigger central types of nystagmus (usually persistent downbeating), which may be the most prominent examination finding in patients with disorders like the Chiari malformation or cerebellar ataxia (Kattah and Gujrati, 2005; Kerber et al., 2005). Positional nystagmus also may be prominent in patients with migraine-associated dizziness (von Brevern et al., 2005). Fistula Testing In patients reporting sound- or pressure-induced dizziness, testing for a defect of the bony capsule of the labyrinth can be performed by pressing and releasing the tragus (small flap of cartilage that can be used to occlude the external ear canal) and observing the eyes for brief associated deviations. Pneumatoscopy (introducing air into the external auditory canal through an otoscope) or Valsalva maneuver performed against pitched nostrils or closed glottis also can trigger associated eye movements. The direction of the triggered nystagmus helps identify the location of the fistula. Gait Assessment Casual gait is examined for initiation, heel strike, stride length, and base width. Patients are then observed during tandem walking and while standing in the Romberg position (with eyes open and then closed). Taken together, a decreased heel strike or stride length, flexed posture, and decreased arm swing suggest Parkinson s disease. A wide-based gait with inability to tandem walk is characteristic of truncal ataxia. Patients with acute vestibular loss will veer toward the side of the affected ear for several days after the event. Patients with peripheral neuropathy or bilateral vestibulopathy may be unable to stand in the Romberg position with eyes closed. Auditory Examination The bedside examination of the auditory system begins with otoscopy. The tympanic membrane normally is translucent; changes in color indicate middle ear disease or tympanosclerosis, a Ch18-H7525.indd /24/07 2:46:41 PM

9 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 245 semicircular crescent or horseshoe-shaped white plaque within the tympanic membrane. Tympanosclerosis is rarely associated with hearing loss but is an important clue to past infections. The area just superior to the lateral process of the malleus should be carefully inspected for evidence of a retraction pocket or cholesteatoma. Findings on otoscopy usually are not associated with causes of dizziness, because the visualized abnormalities typically do not involve the inner ear. The bedside hearing examination is not very sensitive as a screening tool for hearing loss but can provide important information in patients with auditory symptoms. When a patient has auditory complaints or when an audiovestibular disorder is strongly suspected, a standard audiogram should be performed because it more accurately assesses the wide spectrum of the auditory system. The whisper test has been shown to be the most sensitive test in picking up hearing loss at the bedside (Bagai et al., 2006). For this test, the examiner stands behind the patient to prevent lip reading and occludes and masks the non-test ear using a finger to rub and close the external auditory canal. The examiner then whispers a set of three to six random numbers and letters. Overall, the patient is considered to have passed the screening test if he or she repeats at least 50% of the letters and numbers correctly. The Weber and Rinne tests are commonly used bedside tuning fork tests. To conduct the Weber test, the base of a 256-Hz or 512-Hz vibrating tuning fork is placed on the vertex, bridge of the nose, upper incisors, or forehead. The patient is asked if the sound is heard, and whether it is heard in the middle of the head or in both ears equally, toward the left, or toward the right. In a patient with normal hearing, the tone is heard centrally. In asymmetrical or a unilateral hearing impairment, the tone lateralizes to one side. Lateralization indicates an element of conductive impairment in the ear in which the sound localizes, a sensorineural impairment in the contralateral ear, or both. The Rinne test compares the patient s hearing by air conduction with that by bone conduction. The fork is first held against the mastoid process until the sound fades. It is then placed 1 inch from the ear. Normal persons can hear the fork about twice as long by air as by bone conduction. If bone conduction is greater than air conduction, a conductive hearing loss is suggested. DIZZINESS AND VERTIGO SPECIFIC DISORDERS CAUSING VERTIGO Peripheral Vestibular Disorders Peripheral vestibular disorders are important to understand because they are common and readily identified at the bedside and often are missed by frontline physicians (see Table 18-2). Vestibular Neuritis A common clinical presentation seen in the emergency department or outpatient clinic is severe vertigo of rapid onset, with nausea, vomiting, and imbalance. The symptoms gradually resolve over several days, but some symptoms can persist for months. The etiology of this disorder probably is viral because the course generally is benign and self-limited and it occurs in young healthy persons, occasionally in epidemics. Histopathological studies provide evidence of a peripheral vestibular localization and support a viral cause. A viral etiology also is likely in most cases of Bell s palsy and sudden sensorineural hearing loss. The key to the diagnosis of vestibular neuritis is in recognizing the peripheral vestibular pattern of nystagmus and identifying a positive result on the head thrust test, in the setting of vertigo of rapid onset without other neurological symptoms. MRI findings usually are normal in these patients (Strupp et al., 1998a). The course of vestibular neuritis is self-limited, and the mainstay of treatment is symptomatic. A recent study showed improvement in peripheral vestibular function, as measured by caloric testing at 1 year, in patients with vestibular neuritis after receiving methylprednisolone within 3 days of onset, compared with placebo (Strupp et al., 2004). A formal vestibular rehabilitation program can help some patients compensate for the vestibular lesion (Strupp et al., 1998b). Benign Paroxysmal Positional Vertigo BPPV may be the most common cause of vertigo in the general population. Patients typically experience brief episodes of vertigo when getting into and out of bed, turning in bed, bending down and straightening up, or extending the head back to look up. The condition is caused when calcium carbonate debris, dislodged from the otoconial membrane, inadvertently enters a semicircular canal. The debris can be free-floating within the affected canal (canalithiasis) or stuck against the cupula (cupulolithiasis). Repositioning maneuvers are highly effective in removing the debris from the canal, although recurrence is common (see Fig. 18-3) (von Brevern et al., 2006). Once the debris is out of the canal, patients are instructed to avoid extreme head positions to prevent the debris from reentering the canal. Patients also can be taught to perform a repositioning maneuver should they experience a recurrence of the positional vertigo. Ménière s Disease Ménière s disease is characterized by recurrent attacks of vertigo associated with auditory symptoms (hearing loss, tinnitus, and aural fullness) during attacks. Over time, progressive hearing loss develops. Attacks are variable in duration, with most lasting longer than 20 minutes, and are associated with severe nausea and vomiting. The course of the disorder is also highly variable. For some patients, the attacks are infrequent and decrease over time while for others they can become debilitating. Occasionally, auditory symptoms are not appreciated by the patient or identified on interictal audiogram early in the disorder, but these features inevitably develop in all patients with Ménière s disease, usually within the first year. Thus, the term vestibular Ménière s disease, previously used to describe the disorder in patients with recurrent episodes of vertigo but no hearing loss, is no longer used. Although usually a disorder involving only one ear, Ménière s disease becomes bilateral in approximately one third of patients. Endolymphatic hydrops, or expansion of the endolymph relative to the perilymph, is regarded as the etiology though the underlying cause is not clear. The characteristic histopathological changes of endolymphatic hydrops, however, have been identified in temporal bone specimens from patients with no clinical history of Ménière s disease (Merchant et al., 2005). Some patients with well-documented Ménière s disease experi- Ch18-H7525.indd /24/07 2:46:42 PM

10 246 P ART 1 Approach to Common Neurological Problems ence abrupt episodes of falling to the ground without loss of consciousness or associated neurological symptoms. They often report the sensation of being pushed or thrown to the ground. The falls are hard and often result in fractures or other injuries. These episodes have been called otolithic catastrophes of Tumarkin because of the suspicion that they represent acute stimulation of the otoliths. The bedside interictal examination of patients with Ménière s disease may identify asymmetrical hearing, but the results of the head thrust test usually are normal. Treatment initially involves an aggressive low-salt diet and diuretics, although the evidence for benefit of these treatments is poor. Intratympanic gentamicin injections can be effective and are minimally invasive. Sectioning of the vestibular nerve and destruction of the labyrinth are other procedures for patients with intractable disease (Minor et al., 2004). Autoimmune inner ear disease manifests as a fulminant variant of Ménière s disease. Another variant is so-called delayed endolymphatic hydrops, characterized by recurrent episodes of severe vertigo, without auditory symptoms, developing years after a severe unilateral hearing loss caused by a viral or bacterial infection. Vestibular Paroxysmia Vestibular paroxysmia is characterized by brief (seconds in duration) episodes of vertigo, occurring suddenly without any apparent trigger. The disorder may be analogous to hemifacial spasm and trigeminal neuralgia, which are thought to be caused by spontaneous discharges from a partially damaged nerve. In patients with vestibular paroxysmia, usually unilateral dysfunction can be identified on vestibular or auditory testing. Some cases may be caused by compression of cranial nerve VIII by a normal vessel, and surgical removal of the vessel from the nerve may cure the condition in rare cases. Many asymptomatic persons, however, have a normal vessel lying on the eighth nerve (usually the anterior inferior cerebellar artery), so the decision to operate in this delicate region should not be made without strongly weighing the potential benefits against potential complications. A trial of an antiepileptic drug such as carbamazepine is clearly indicated before surgery is undertaken (Moon and Hain, 2005). Vestibular Fistulas Superior canal dehiscence was first described in 1998 (Minor et al., 1998). As the name implies, dehiscence of the bone overlying the superior canal results in formation of a fistula between the superior canal and the middle cranial fossa. Normally the semicircular canals are enclosed by the rigid bony capsule and are unaffected by sound pressure changes. The oval and round windows direct the forces associated with sound waves into the cochlea and along the spiral basilar membrane. A break in the bony capsule of the semicircular canals can redirect some of the sound or pressure to the semicircular canals causing vestibular activation, a phenomenon known as Tulio s phenomenon. Before the recognition of superior canal dehiscence, fistulas were known to occur with rupture of the oval or round window or erosion into the horizontal semicircular canal from chronic infection. Pressure changes generated by increasing intracranial pressure (Valsalva maneuver performed against a closed glottis) or increasing middle ear pressure (Valsalva maneuver performed against pinched nostrils or compression of the tragus) trigger brief nystagmus in the plane of the affected canal. Surgical repair of the fistula may be effective treatment in some cases. Patients with this disorder may have hypersensitivity to boneconducted sound and low bone conduction thresholds on the audiogram, even though air conduction thresholds remain normal (Minor, 2005). Other vestibular fistulas can result from trauma or erosion of a cholesteatoma into the horizontal semicircular canal. Other Peripheral Disorders Many other peripheral vestibular causes of vertigo have been recognized, but most are uncommon. Vertigo often follows a blow to the head, even without a corresponding temporal bone fracture. This so-called labyrinthine concussion results from the susceptibility of the delicate structures of the inner ear to blunt trauma. Vestibular ototoxicity, usually from gentamicin, can cause a vestibulopathy that usually is bilateral but rarely can be unilateral (Waterston and Halmagyi, 1998). Although the most prominent symptoms are oscillopsia and imbalance, some nonspecific dizziness may occur as well. Acoustic neuromas (vestibular schwannomas) typically manifest with slowly progressive unilateral hearing loss, but vertigo can occur only rarely. Because the tumor growth is slow, the vestibulopathy is compensated by the central nervous system. Finally, any disorder affecting the skull base, such as sarcoidosis, lymphoma, bacterial and fungal infections, or carcinomatous meningitis, can cause peripheral vestibular symptoms. Central Nervous System Disorders The key to the diagnosis of central nervous system disorders in patients presenting with dizziness is the presence of other focal neurological symptoms or identifying central ocular motor abnormalities or ataxia. Because central disorders can mimic peripheral vestibular disorders, the most effective approach in patients with isolated dizziness is first to rule out common peripheral causes. Brainstem or Cerebellar Ischemia/Infarction Ischemia affecting vestibular pathways within the brainstem or cerebellum often causes vertigo. Brainstem ischemia normally is accompanied by other neurological signs and symptoms, because motor and sensory pathways are in close proximity to vestibular pathways. Vertigo is the most common symptom with Wallenberg s syndrome, characterized by infarction in the lateral medulla in the territory of the posterior inferior cerebellar artery (PICA), but other neurological symptoms and signs (e.g., diplopia, facial numbness, Horner s syndrome) invariably are present (see Chapter 21). Ischemia of the cerebellum can cause vertigo as the most prominent or only symptom, and a common dilemma is whether the patient with acute-onset vertigo needs an MRI study to rule out cerebellar infarction. CT scans of the posterior fossa are not sensitive for excluding ischemia (Wasay and Halmagyi, 2005). Abnormal ocular motor findings in patients with brainstem or cerebellar strokes include (1) spontaneous nystagmus that is purely vertical, horizontal, or Ch18-H7525.indd /24/07 2:46:42 PM

11 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 247 torsional; (2) direction changing gaze-evoked nystagmus (the patient looks to the left and has left-beating nystagmus, then looks to the right and has right-beating nystagmus); (3) impairment of smooth pursuit; and (4) overshooting saccades. Rarely, central causes of nystagmus can closely mimic the peripheral vestibular pattern of spontaneous nystagmus (Lee and Cho, 2004). Multiple Sclerosis Dizziness is a common symptom in patients with multiple sclerosis (MS), and vertigo is the initial symptom in approximately 5% of patients. A typical MS attack has a gradual onset, reaching its peak within a few days. Milder spontaneous episodes of vertigo, not characteristic of a new attack, and positional vertigo lasting seconds also are common in MS patients. The key to the diagnosis is to find lesions disseminated in time and space within the nervous system. Nearly all varieties of central spontaneous and positional nystagmus occur with MS, and occasionally patients show typical peripheral vestibular nystagmus when the lesion affects the root entry zone of the vestibular nerve. MRI of the brain identifies white matter lesions in approximately 95% of patients with MS, although similar lesions sometimes are seen in patients without the clinical criteria for the diagnosis of MS. Posterior Fossa Structural Abnormalities Any structural lesion of the posterior fossa can cause dizziness. With the Chiari malformation, the brainstem and cerebellum are elongated downward into the cervical canal, causing pressure on both the caudal midline cerebellum and the cervicomedullary junction. The most common neurological symptom is a slowly progressive unsteadiness of gait, which patients often describe as dizziness. Vertigo and hearing loss are uncommon, occurring in approximately 10% of patients. Spontaneous or positional downbeat nystagmus is particularly common with Chiari malformations, but other forms of central nystagmus also occur. Dysphagia, hoarseness, and dysarthria can result from stretching of the lower cranial nerves, and obstructive hydrocephalus can result from occlusion of the basilar cisterns. MRI is the procedure of choice for identifying Chiari malformations; midline sagittal sections clearly show the level of the cerebellar tonsils. The most common central nervous system tumors in the posterior fossa are gliomas in adults and medulloblastoma in children. Ocular motor dysfunction (impaired smooth pursuit, overshooting saccades), impaired coordination, or other central nervous system abnormalities occur in these patients. An early finding in patients with cerebellar tumors can be central positional nystagmus. Vascular malformations (arteriovenous malformations, cavernous hemangiomas) similarly can cause dizziness but generally are asymptomatic until bleeding occurs, at which time they can be life-threatening. Neurodegenerative Disorders It is not uncommon for a patient with the main complaint of dizziness to have, or later develop, typical features of Parkinson s disease, a parkinsonian syndrome (progressive supranuclear palsy, multiple systems atrophy), or a progressive ataxia disorder (de Lau et al., 2006). Usually, however, dizziness in these patients is better clarified as imbalance. Positional downbeat nystagmus occurs in patients with spinocerebellar ataxia type 6 (SCA6) and other progressive ataxia disorders (Kattah and Gujrati, 2005; Kerber et al., 2005). Epilepsy Vestibular symptoms are common with focal seizures, particularly those originating from the temporal and parietal lobes. The key to differentiating vertigo with seizures from other causes of vertigo is the almost invariable association of seizures with an altered level of consciousness. Episodic vertigo as an isolated manifestation of a focal seizure is a rarity, if it occurs at all. Vertigo in Inherited Disorders The clinical evaluation of patients presenting with dizziness has traditionally hinged on the history of present illness and examination. With the recent rapid advances in molecular biology, however, many causes of vertigo have been found to have a strong genetic component. Obtaining a complete family history is therefore very important, particularly in patients without a specific identifiable cause for their dizziness. Because the symptoms of these familial disorders often are not debilitating and can be highly variable, simply asking the patient about a family history at the time of the appointment may not be adequate. The patient should be instructed to specifically interview other family members regarding the occurrence of these symptoms. Migraine Migraine is a heterogeneous genetic disorder characterized by headaches in addition to many other neurological symptoms. Several rare monogenetic subtypes have been identified. Linkage analysis has identified a number of chromosomal loci in common forms of migraine, but no specific genes have been found. Benign recurrent vertigo usually is a migraine equivalent because no other signs or symptoms develop over time, neurological examination findings remain normal, and a family or personal history of migraine headaches is common, as are typical migraine triggers. Some patients with benign recurrent vertigo (BRV) also report auditory symptoms similar to those described by patients with Ménière s disease, and a mild hearing loss also may be evident on the audiogram (Battista, 2004). The key factor distinguishing between migraine and Ménière s disease is the lack of progressive unilateral hearing loss in patients with migraine. Positional vertigo also may occur in patients with migraine (von Brevern et al., 2005). The cause of vertigo in migraine patients is not known. Long-standing motion sensitivity including carsickness, sensitivities to other types of stimuli, and a clear family history of migraine help support the diagnosis. Although the diagnosis of migraine-associated dizziness remains one of exclusion, little else can cause recurrent episodes without any other symptoms over a long period of time. In a genome-wide linkage scan in BRV patients (20 families), linkage to chromosomal region 22q12 was found, but genetic heterogeneity was evident (Lee et al., 2006). Testing linkage Ch18-H7525.indd /24/07 2:46:42 PM

12 248 P ART 1 Approach to Common Neurological Problems using a broader phenotype of BRV and migraine headaches weakened the linkage signal. Thus, no evidence exists at this time that migraine is allelic with BRV, even though migraine has a high prevalence among BRV patients. Familial Bilateral Vestibulopathy In familial bilateral vestibulopathy (FBV), patients typically have brief attacks of vertigo (seconds in duration), followed by progressive loss of peripheral vestibular function leading to imbalance and oscillopsia, usually with onset by the fifth decade of life. Quantitative rotational testing shows gains greater than 2 standard deviations below the normal mean for both sinusoidal and step changes in angular velocity. Caloric testing is insensitive for identifying bilateral vestibulopathy because of the wide range of normal caloric responses. The bedside head thrust test may show bilateral corrective saccades when vestibulopathy is severe. As the vestibulopathy becomes more severe, attacks of vertigo become less frequent and eventually cease. In contrast with the genetic causes of hearing loss for which 46 distinct dominantly inherited genetic syndromes are recorded (Van Camp and Smith, 2006) only a few families afflicted with FBV have been described (Brantberg, 2003; Jen et al., 2004b). This disparity may be explained by the difficulty in identifying such families; quantitative vestibular function testing is available only at major medical centers. Additionally, patients with FBV may not present to doctors for evaluation if they have adequately compensated for the vestibular loss with other sensory systems. Despite the profound vestibular loss, hearing remains normal. Linkage analysis performed in four families with FBV maps to a chromosomal locus on 6q (Jen et al., 2004b). This region does not overlap that for any known autosomal dominant deafness or migraine syndromes. Familial Hearing Loss and Vertigo Familial progressive vestibular-cochlear dysfunction was first identified in Linkage to chromosomal locus 14q12-13 was later found, and the disorder was designated DFNA9 (DFNA = deafness, familial, nonsyndromic, type A [autosomal dominant inheritance]) (Manolis et al., 1996). Using an organspecific approach, mutations within COCH were found to cause DFNA9 (Robertson et al., 1998). This disorder of progressive hearing loss is unique because no other genetic hearing loss syndromes of autosomal dominant inheritance have vertigo as a common symptom. Progressive hearing loss is the most prominent symptom of DFNA9, and vertigo occurs in approximately 50% of patients. When present, vertigo may be spontaneous or positionally triggered (Lemaire et al., 2003). Age at onset is variable, with symptoms developing in the second to third decade of life in some patients and appearing later in others. Vertigo attacks last minutes to hours and can be accompanied by worsening of hearing, aural fullness, or tinnitus, thus closely mimicking Ménière s syndrome. Vertigo episodes can precede or accompany onset of hearing loss. In addition to severe progressive hearing loss, eventually DFNA9 patients develop progressive loss of vestibular function and corresponding symptoms of imbalance and oscillopsia. Because some patients have attacks closely resembling those in Ménière s syndrome, the COCH gene was screened for mutations in idiopathic Ménière s disease patients, but none were found. No studies report the use of effective treatments for vertigo attacks, but as with FBV, these attacks generally last only a few years and then become less frequent, presumably as a result of loss of vestibular function. Enlarged vestibular aqueduct syndrome (EVA), designated DFNB4 (DFNB = deafness, familial, nonsyndromic, type B [autosomal recessive inheritance]), is characterized by early-onset hearing loss with enlargement of the vestibular aqueduct, best seen on temporal bone computed tomography. The vestibular aqueduct normally is less than 1.5 mm in diameter, but in EVA it is much larger. The mechanism leading to hearing loss and vertigo is not clear. The vestibular aqueduct contains the endolymphatic duct, which connects the medial wall of the vestibule to the endolymphatic sac and is an important structure in the exchange of endolymph. The enlargement may cause increased transmission of intracranial pressures to the inner ear structures. Nevertheless, the Valsalva maneuver, which increases intracranial pressure, does not trigger symptoms in patients with EVA. Vertigo attacks last 15 minutes to 3 hours and are not associated with changes in hearing. Vertigo attacks may begin at the onset of hearing loss (early childhood) or years later and can be triggered by blows to the head or vigorous spinning (Oh et al., 2001b). Quantitative vestibular testing may give normal results in patients with EVA or may reveal mild to moderate loss of vestibular function. Enlargement of the vestibular aqueduct also has been observed in Pendred s syndrome (PS), in branchiootorenal syndrome, with the CHARGE association (coloboma, heart disease, atresia choanae, retardation of growth and development and/or central nervous system anomalies, genital hypoplasia, ear anomalies and/or deafness), in Waardenburg s syndrome, and in distal renal tubular acidosis with deafness. EVA syndrome is allelic to PS, which is characterized by developmental abnormalities of the cochlea in combination with thyroid dysfunction and goiter. Familial Ataxia Syndromes Vestibular symptoms and signs are common with several of the hereditary ataxia syndromes, including spinocerebellar ataxia types 1, 2, 3, 6, and 7; Friedreich s ataxia; Refsum s disease; and episodic ataxia (EA) types 2, 3, 4, and 5 (see Chapter 76). In most of these disorders, the symptoms are slowly progressive, with the cerebellar ataxia and incoordination overshadowing the vestibular symptoms. Head movement induced oscillopsia commonly occurs because the patient is unable to suppress the VOR with fixation. Attacks of vertigo may occur in up to half of patients with SCA6 (Takahashi et al., 2004), many of which are positionally triggered (Jen et al., 1998). Persistent down-beating nystagmus often is seen in patients placed in the head-hanging position. The positional vertigo and nystagmus can even be the initial symptom in these patients. Most of the episodic ataxia syndromes have onset before the age of 20 (Jen et al., 2004a). The attacks are characterized by extreme incoordination, leading to severe difficulty in walking during attacks. Vertigo can occur as part of these attacks, and migraine headaches are common. In fact, EA2, SCA6, and familial hemiplegic migraine type 1 all are caused by mutations within the same gene, CACNA1A. An additional feature of EA2 and EA4 is the eventual development of interic- Ch18-H7525.indd /24/07 2:46:42 PM

13 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 249 tal nystagmus and progressive ataxia. Patients with EA2 often exhibit a dramatic response to treatment with acetazolamide. COMMON CAUSES OF NONSPECIFIC DIZZINESS Patients with nonspecific dizziness probably are referred to neurologists more frequently than patients with true vertigo. These patients usually are bothered by lightheadedness ( wooziness ), presyncope, imbalance, motion sensitivity, or anxiety. Side effects and toxicity from medications are common causes of nonspecific dizziness. Bothersome lightheadedness can be a direct effect of the medication itself or the result of lowering of the patient s blood pressure. Ataxia can be caused by antiepileptic medications and usually is reversible once the medication is decreased or stopped. Patients with peripheral neuropathy causing dizziness report significant worsening of their balance in poor lighting and also the sensation that they are walking on cushions. Patients with panic attacks can present with nonspecific dizziness, but their spells invariably are accompanied by other symptoms or signs such as sense of fear or doom, palpitations, sweating, shortness of breath, or paresthesias. Other medical conditions such as cardiac arrhythmias or metabolic disturbances can cause nonspecific dizziness. In the elderly, confluent white matter hyperintensities have a strong association with dizziness and balance problems. Presumably the result of small vessel arteriosclerosis, decreased cerebral perfusion (Marstrand et al., 2002) has been identified in these patients even when blood pressure taken at the arm is normal. Patients with dizziness associated with white matter hyperintensities on MRI usually feel better sitting or lying down and typically have impairment of tandem gait. Because many elderly patients are taking blood pressure medications, at least a trial of lowering or discontinuing these medications may be warranted. COMMON PRESENTATIONS OF VERTIGO Patients present with symptoms, rather than with specific diagnosable disorders. The most common presentations of vertigo are described next. Acute Severe Vertigo The patient presenting with new-onset severe vertigo probably has vestibular neuritis, but stroke also should be a concern. An abrupt onset with accompanying focal neurological symptoms, particularly those that can be related to the posterior circulation, suggests an ischemic stroke. If no significant abnormalities are noted on the general neurological examination, attention should focus on the neurotological evaluation. If no spontaneous nystagmus is observed, a technique to block visual fixation should be applied. The direction of the nystagmus should be noted and the effect of gaze assessed. If a peripheral vestibular pattern of nystagmus is identified, a positive result on head thrust testing localizes the lesion to the vestibular nerve. In young patients, the diagnosis is vestibular neuritis. This also is probably the most common diagnosis in older patients, but acute ischemia of the vestibular nerve or vestibular labyrinth cannot be excluded. When the head thrust test gives a negative result (i.e., no catch-up saccades are present), the possibility of a small brainstem or cerebellar stroke that mimics vestibular neuritis should be considered (Lee and Cho, 2004; Norrving et al., 1995; Thomke and Hopf, 1999). If hearing loss accompanies the episode, labyrinthitis is the most likely diagnosis, but auditory involvement does not exclude a vascular cause, because the anterior inferior cerebellar artery supplies both the inner ear and brain. When hearing loss and facial weakness accompany acute-onset vertigo, the examiner should closely inspect the outer ear for vesicles characteristic of herpes zoster (Ramsay Hunt syndrome). An acoustic neuroma is a slow-growing tumor and thus does not typically cause acute-onset vertigo. Migraine can mimic vestibular neuritis, although the diagnosis of migraine-associated vertigo hinges on recurrent episodes and lack of progressive auditory symptoms. Recurrent Attacks of Vertigo In patients with recurrent attacks of vertigo, the key diagnostic information lies in the details of the attacks. Ménière s disease is the likely cause in patients with recurrent vertigo lasting longer than 20 minutes and associated with unilateral auditory symptoms. If the Ménière s-like attacks manifest in a fulminant fashion, the diagnosis of autoimmune inner ear disease should be considered. Transient ischemic attacks (TIAs) should be suspected in patients who experience brief episodes (minutes in duration) of vertigo, particularly when vascular risk factors are present and other neurological symptoms are reported. Case series of patients with rotational vertebral artery syndrome demonstrate that the inner ear and possibly central vestibular pathways have high energy requirements and are therefore susceptible to levels of ischemia tolerated by other parts of the brain (Choi et al., 2005). The migraine equivalent, benign recurrent vertigo, is characterized by a history of similar symptoms, normal findings on physical examination, family or personal history of migraine headaches, and typical triggers. Attacks are otherwise highly variable, lasting anywhere from seconds to days. If the duration of attacks is consistently only seconds, the diagnosis of vestibular paroxysmia should be considered. Recurrent Positional Vertigo Positional vertigo is defined by the symptom being triggered, not simply worsened, by certain position changes. In the patient complaining of recurrent episodes of vertigo triggered by certain head movements, the likely diagnosis is BPPV, but this is not the only possibility. BPPV can be identified and treated at the bedside, so positional testing should be performed in any patient with this complaint. Positional testing also can uncover the other causes of positionally triggered dizziness (Bertholon et al., 2002). The history strongly suggests the diagnosis of BPPV when the positional vertigo is brief (duration less than 1 minute), has typical triggers, and is unaccompanied by other neurological symptoms. A burst of vertical torsional nystagmus is specific for BPPV of the posterior canal (Aw et al., 2005). Ch18-H7525.indd /24/07 2:46:43 PM

14 250 P ART 1 Approach to Common Neurological Problems If the result of the Dix-Hallpike test is negative, the examiner should search for the horizontal canal variant of BPPV. Central positional nystagmus occurs as the result of disorders affecting the posterior fossa including tumors, cerebellar degeneration, Chiari malformation, and MS. The nystagmus of these disorders typically is downbeating and persistent, although a pure torsional nystagmus may occur as well. Following loss of one vertebral artery, vertigo or significant dizziness after head turns to the direction opposite the intact artery may develop, because the bony structures of the spinal column can pinch off the remaining vertebral artery (Choi et al., 2005). Central types of nystagmus develop as a result, and vertigo can be the most prominent symptom. Finally, migraine also can closely mimic BPPV (von Brevern et al., 2005). Patients with migraine as the cause typically report a longer duration of symptoms once the positional vertigo is triggered, and the nystagmus may be of a central or peripheral type. HEARING LOSS Neurologists generally do not encounter patients principally bothered by auditory symptoms, such as hearing loss or tinnitus, as opposed to patients with dizziness, who frequently are referred for evaluation. Nevertheless, an understanding of the auditory system, certain disorders causing auditory symptoms, and audiograms can enhance the diagnostic abilities of the neurologist. CLASSIFICATION OF HEARING LOSS Hearing loss can be classified as conductive, sensorineural, or central based on the anatomical site of the pathological process. Conductive Hearing Loss Conductive hearing loss results from lesions involving the external or the middle ear. The tympanic membrane and ossicles act as a transformer, amplifying the airborne sound and effectively transferring it to the inner ear fluid. If this normal pathway is obstructed, transmission can occur across the skin and through the bones of the skull (bone conduction) but at the cost of significant energy loss. Patients with a conductive hearing loss can hear speech in a noisy background better than in a quiet background, because they can understand loud speech as well as anyone. The most common cause of conductive hearing loss is impacted cerumen in the external canal. The most common serious cause of conductive hearing loss is otitis media, which can result from accumulation of either infected fluid (suppurative otitis) or noninfected fluid (serous otitis) in the middle ear, where it impairs the conduction of air-borne sound. With chronic otitis media, a cholesteatoma may erode the ossicles. Otosclerosis produces progressive conductive hearing loss by immobilizing the stapes with new bone growth. Other common causes of conductive hearing loss are trauma, congenital malformations of the external and middle ear, and glomus body tumors. Sensorineural Hearing Loss Sensorineural hearing loss may be secondary to lesions of the cochlea, the auditory division of the acoustic nerve, or both, and results in inability to perceive both bone- and air-conducted sound normally. The spiral cochlea mechanically analyzes the frequency content of sound. For high-frequency tones, only sensory cells in the basilar turn are activated, but for low-frequency tones, all sensory cells are activated. Therefore, with lesions of the cochlea and its afferent nerve, the hearing levels for different frequencies usually are unequal, and the phase relationship between different frequencies may be altered. Patients with sensorineural hearing loss often have difficulty hearing speech that is mixed with background noise, and they may be annoyed by loud speech. Distortion of sounds is common; a pure tone may be heard as noisy, rough, or buzzing, or it may be distorted so that it sounds like a complex mixture of tones. Central Hearing Loss Central hearing loss results from lesions of the central auditory pathways. These lesions involve the cochlear and dorsal olivary nuclear complexes, inferior colliculi, medial geniculate bodies, auditory cortex in the temporal lobes, and interconnecting afferent and efferent fiber tracts. As a rule, patients with central lesions do not have impaired hearing levels for pure tones, and they understand speech so long as it is clearly spoken in a quiet environment. If the listener s task is made more difficult with the introduction of background or competing messages, performance deteriorates more markedly in patients with central lesions than it does in normal persons. Lesions involving the eighth nerve root entry zone or cochlear nucleus (demyelination or infarction in the lateral pontomedullary region), however, can cause unilateral hearing loss for pure tones. Because approximately half of afferent nerve fibers cross central to the cochlear nucleus, this is the most central structure in which a lesion can result in a unilateral hearing loss. SPECIFIC DISORDERS CAUSING HEARING LOSS Ménière s Disease Auditory symptoms in Ménière s disease consist of a fluctuating sense of fullness and pressure, along with tinnitus and decreased hearing in one ear. In the early stages, the hearing loss is completely reversible, but in later stages, a residual hearing loss remains. Tinnitus may persist between episodes but usually increases in intensity immediately before or during the acute episode. It typically is described as a roaring like the sound of the ocean or a hollow seashell. In the early stages, evidence of hearing loss in the low frequencies appears on the audiogram. As the disorder progresses, a more complete hearing loss occurs. In approximately 30% of patients, the disorder becomes bilateral. Eventually, severe permanent hearing loss develops, and the episodic nature spontaneously disappears. When the hearing loss, particularly when bilateral, is fulminant and rapidly progressive, the diagnosis of autoimmune inner ear disease should be considered. (See also see earlier section on Ménière s disease under Specific Disorders Causing Vertigo. ) Ch18-H7525.indd /24/07 2:46:43 PM

15 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 251 Cerebellopontine Angle Tumors Acoustic neuromas (vestibular schwannoma) account for about 5% of intracranial tumors and more than 90% of cerebellopontine angle tumors. These tumors usually begin in the internal auditory canal, producing symptoms by compressing the nerve in its narrow confines. As the tumor grows, it protrudes through the internal auditory meatus with stretching of adjacent nerves over the surface of the mass, and deforms the cerebellum and brainstem. By far the most common symptoms associated with the acoustic neuromas are slowly progressive unilateral hearing loss and tinnitus from compression of the cochlear nerve. Rarely, acute hearing loss occurs, apparently from compression of the labyrinthine vasculature. Vertigo occurs infrequently, but approximately half of the patients with an acoustic neuroma complain of mild imbalance or disequilibrium. An epidermoid tumor, meningioma, facial nerve schwannoma, or metastatic disease also can cause mass lesions within the cerebellopontine angle. The audiometric pattern is variable, but patients with angle tumors causing hearing loss usually have poor speech discrimination, acoustic reflex decay, and pure tone decay, rather than a marked asymmetry of pure tones. Superior Canal Dehiscence Patients with superior canal dehiscence may experience conductive hyperacusis (hearing their eye move or the impact of their feet during walking or running) and autophony (hearing their own breath and voice sounds) in the affected ear. An airbone gap often is identified on standard audiograms. The Weber tuning fork test typically permits lateralization to the affected ear, and the Rinne turning fork test may show bone conduction greater than air conduction. (See also section under Specific Disorders Causing Vertigo. ) Otosclerosis Otosclerosis is a metabolic disease of the bony labyrinth that usually manifests itself by immobilizing the stapes, thereby producing a conductive hearing loss. A positive family history for otosclerosis is reported in 50% to 70% of cases. Bilateral involvement is usual, but approximately one fourth of cases are unilateral. Conductive hearing loss is the hallmark of otosclerosis, but a combined conductive-sensorineural hearing loss pattern is frequent. Although otosclerosis is primarily a disorder of the auditory system, vestibular symptoms and signs are more common than is generally appreciated. Noise-Induced Hearing Loss Noise-induced hearing loss is extremely common in today s industrialized society. Approximately one third of people with hearing loss can attribute at least part of the loss to noise exposure. The loss almost always begins at 4000 Hz, creating the typical notched appearance on the audiogram, and does not affect speech discrimination until late in the disease process. Typically, levels of noise exposure greater than 85 db are required to cause the changes in the ear induced by loud noise. Examples of noise greater than 85 db that are common sources of exposure include motorcycles, firecrackers, factory machinery, and music concerts. Genetic Disorders Familial hearing loss syndromes with vertigo are discussed earlier under Familial Hearing Loss and Vertigo. Currently, 46 genetically defined autosomal dominant hearing loss disorders have been identified, as well as an additional 54 autosomal recessive disorders and 5 X-linked disorders (Van Camp and Smith, 2006). These disorders typically start early in life and cause profound hearing loss. Vestibular symptoms are not common. Ototoxicity The most common medications causing hearing loss are aminoglycoside antibiotics, loop diuretics, and cisplatin. Impaired elimination of these drugs, such as occurs with renal insufficiency, predisposes affected patients to ototoxicity. Patients receiving high-dose salicylate therapy frequently complain of hearing loss, tinnitus, and dizziness, which are rapidly reversible after cessation of the salicylate ingestion. COMMON PRESENTATIONS OF HEARING LOSS Asymmetrical Sensorineural Hearing Loss The evaluation of patients identified as having an asymmetrical sensorineural hearing loss is primarily the search for a tumor in the area of the internal auditory canal or cerebellopontine angle, or more rarely other lesions of the temporal bone or brain. With an asymmetry of hearing defined as 15 db or greater in two or more frequencies, or a 15% or more asymmetry in speech discrimination scores, approximately 10% of patients will have lesions identified on MRI (Cueva, 2004). Acoustic neuromas are by far the most common abnormality found. Other causative lesions may include glomus jugulare tumors, ectatic basilar artery with brainstem compression, or petrous apex cholesterol granuloma. Auditory brainstem response testing shows sensitivity and specificity of approximately 70%, with a false-positive rate of 77% but a false-negative rate of 29% (Cueva, 2004). Sudden Sensorineural Hearing Loss The etiology of sudden sensorineural hearing loss is similar to that in both Bell s palsy and vestibular neuritis in that a viral cause is presumed in a majority of cases, but proof of a viral pathophysiology in a given case is difficult to obtain. The hearing loss can develop abruptly or evolve over several hours. Acoustic neuromas may be found in approximately 5% of patients with this presentation (Aarnisalo et al., 2004), but the clinician also should be aware of the possibility of false- Ch18-H7525.indd /24/07 2:46:43 PM

16 252 P ART 1 Approach to Common Neurological Problems positive findings on MRI, particularly for lesions less than 6 mm in diameter (Arriaga et al., 1995). Focal ischemia affecting the cochlea, cochlear nerve, or the root entry zone also can cause an abrupt loss of hearing over several minutes. In a patient at risk for stroke, this cause should be considered early because it can be the harbinger of basilar artery occlusion (Toyoda et al., 2002). Sudden-onset bilateral hearing loss rarely can result from bilateral lesions of the primary auditory cortex in the transverse temporal gyri of Heschl. Deficits can range from auditory agnosia for speech or nonspeech sounds, with rela tively normal hearing thresholds, to rare cases of cortical deafness, characterized by markedly elevated pure tone thresholds. Hearing Loss with Age The bilateral hearing loss commonly associated with advancing age is called presbycusis. It is not a distinct entity but rather represents multiple effects of aging on the auditory system. It may include conductive and central dysfunction, but the most consistent effect of aging is on the sensory cells and the neurons of the cochlea. The typical audiogram appearance in patients with presbycusis is that of symmetrical hearing loss, with the tracing gradually sloping downward with increasing frequency. The most consistent pathological condition associated with presbycusis is a degeneration of sensory cells and nerve fibers at the base of the cochlea. TINNITUS Tinnitus is a noise in the ear that usually is audible only to the patient, although occasionally the sound can be heard by the examining physician. It is a symptom that can be associated with a variety of disorders that may affect the ear or the brain. The most important piece of information is whether the patient localizes it to one or both ears, or whether it is nonlocalizable. As a general rule, tinnitus localized to one ear will have an identifiable cause, but not when localized to both ears or nonlocalizable. The characteristics of the tinnitus can provide helpful information. For example, the typical tinnitus associated with Ménière s disease is described as a roaring sound, like listening to a seashell. The tinnitus associated with an acoustic neuroma typically is a high-pitched ringing or resembles the sound of steam blowing from a tea kettle. If the tinnitus is rhythmic, the patient should be asked whether it is synchronous with the pulse or with respiration. Recurrent rhythmic or even nonrhythmic clicking sounds in one ear can indicate stapedial myoclonus. The most common form of tinnitus is a bilateral high-pitched sound that usually is worse at night when it is quiet, with less background noise to mask it. It also may worsen when the patient is under stress, or with the use of caffeine. CLINICAL INVESTIGATIONS DIZZINESS AND VERTIGO The history and physical examination should determine what diagnostic tests, if any, are necessary in patients presenting with dizziness or vertigo. Studies have repeatedly shown that MRI, audiogram, and vestibular tests are no different in unselected patients complaining of dizziness when compared with agematched controls (Colledge et al., 1996, 2002; Hajioff et al., 2002; Lawson et al., 1999; Yardley et al., 1998). Many disorders causing dizziness can be diagnosed and even treated on the initial encounter with no further diagnostic tests indicated. General Tests General tests such as blood chemistry panels, chest x-ray studies, or electrocardiograms are indicated only when the clinician is searching for a specific abnormality. If a patient has otherwise unexplained nonspecific dizziness, ruling out metabolic causes is indicated. Imaging Brain imaging commonly is ordered in patients complaining of dizziness. Although a CT scan can rule out a large mass, smaller lesions cannot be excluded, because of artifact and poor resolution in the posterior fossa (Wasay et al., 2005). MRI is the imaging modality of choice but is expensive. Determining which patients should have an MRI can be difficult; an understanding of the common peripheral vestibular disorders is important for making this decision. Patients identified as having BPPV, vestibular neuritis, or Ménière s disease do not require an imaging study. In addition, patients with normal findings on neurological and neurotological examinations who report episodes of dizziness dating back more than several months are unlikely to have a significant abnormality on MRI. Although studies show improved hearing preservation after surgery in patients with acoustic neuromas when diagnosed early, this does not mean every patient complaining of dizziness requires an MRI to exclude this cause. Acoustic neuromas are rare, whereas dizziness and vertigo are extremely common. In dizzy patients with gradually progressive hearing loss, MRI may be helpful. Vestibular Testing Vestibular testing consists of both ENG (or videonystagmography) and rotational chair testing (Fife et al., 2000; Furman et al., 1996). A standard ENG test battery includes tests of visual ocular control (saccades, smooth pursuit, and optokinetic nystagmus), a search for pathological nystagmus with fixation and with eyes open in darkness, and a bithermal caloric test (Baloh and Honrubia, 2001). Standard rotational testing applies multiple graded vestibular stimuli over short periods of time and also can be used for tests of visual-vestibular interaction (fixation suppression of the VOR). Vestibular testing can help identify and quantify a unilateral or bilateral vestibular loss and ocular motor abnormalities. The usefulness of vestibular testing is highly dependent on both test administration and test interpretation. No agency in the United States monitors or credentials persons administering or interpreting vestibular tests. Furthermore, artifacts are common, and patient cooperation must be maintained throughout the test. With most subtests, either ranges of normal are wide or standards have not been set. These issues contribute to the large degree of variability in vestibular testing and thus to variable results from laboratory to Ch18-H7525.indd /24/07 2:46:43 PM

17 C HAPTER 18 Dizziness, Vertigo, and Hearing Loss 253 laboratory. Despite these issues, reliable and clinically useful results can be obtained from the numerous specialty centers and community-based groups that have the requisite skills, ability, and knowledge. Caloric testing is used mainly to identify a unilateral vestibulopathy. Rotational chair testing, used principally to identify a bilateral vestibulopathy, is not readily available outside of academic centers. Abnormal findings on these tests must be put in the context of the patient s presentation and clinical findings. Thus, even a decreased caloric response on one side does not mean the patient s symptoms are peripheral unless the clinical presentation fits. Most laboratories require a caloric asymmetry of 25% to 30% to indicate a significant reduced caloric response on one side. Even with use of this criterion, finding a caloric asymmetry is not uncommon in normal control subjects, particularly those with diabetes or migraine. Additionally, impaired smooth pursuit or slow saccades should not be used to make a central diagnosis if the patient did not understand instructions or was overly tired or sedated. Vestibular testing is particularly helpful in identifying the affected side in patients with Ménière s disease, although the most localizing test is the audiogram. BPPV is a bedside diagnosis, and vestibular neuritis can be diagnosed at the bedside as well. Vestibular testing does not add additional information in patients with BPPV, in patients diagnosed with vestibular neuritis who have a positive result on the head thrust test, or in patients with bedside central nervous system findings unless quantifying the abnormality is important. Although patients with a bilateral vestibulopathy generally can be identified at the bedside with bilateral catch-up saccades, rotational chair testing can pick up more subtle impairment. Auditory Testing Because of well-established standards and formal certified training programs, audiograms are a reliable and reproducible test. Testing is not subject to the many artifacts and subjective interpretations of vestibular testing. Because the hearing and balance organs are close to one another and connected as part of the labyrinth, share overlapping vascular supply, and have key nervous system components in close proximity with a common trunk entering the brain stem, a lesion of one system generally affects the other. For patients complaining of vertigo, with or without hearing loss, obtaining an audiogram may be helpful in making a diagnosis or at least in establishing the patient s baseline hearing for later comparison. Although Ménière s disease is characterized by hearing loss in addition to vertigo and tinnitus, the auditory symptoms may not develop in the early stages, or patients may not perceive the hearing loss. HEARING LOSS AND TINNITUS Virtually every patient with complaints of hearing loss or tinnitus should undergo a standard audiogram. Any patient with unilateral symptoms who may be a surgical candidate also should have an MRI study with gadolinium to evaluate for a cerebellopontine angle mass. No study provides predictive information regarding which patients with sudden sensorineural hearing loss are most likely to have a causative lesion identified by MRI. References Aarnisalo, A. A., Suoranta, H., & Ylikoski, J. 2004, Magnetic resonance imaging findings in the auditory pathway of patients with sudden deafness, Otol Neurotol, vol. 25, pp Adams, P. F., Hendershot, G. E., & Marano, M. 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