SHAKE, RATTLE, AND ROLL: TOP 10 THINGS YOU SHOULD KNOW ABOUT VESTIBULAR DISEASE

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1 SHAKE, RATTLE, AND ROLL: TOP 10 THINGS YOU SHOULD KNOW ABOUT VESTIBULAR DISEASE Jared B. Galle, DVM, Diplomate ACVIM (Neurology) Dogwood Veterinary Referral Center 4920 Ann Arbor-Saline Road Ann Arbor, MI Introduction The vestibular system is essential in maintaining balance and preventing an animal from falling over. Head tilt, falling, rolling, leaning, circling, nystagmus, and ataxia are common signs of a problem in the vestibular system. Clinical signs of vestibular disease may result from a lesion involving the peripheral vestibular components (receptors in the inner ear or vestibular portion of cranial nerve 8) or the central vestibular components (brainstem vestibular nuclei or vestibular centers in the cerebellum). Knowing the neurologic signs that result from a lesion in each component is important in determining potential causes and what diagnostics to perform. This lecture will review the clinical approach to a patient with vestibular disease. 1. What are the most common signs of vestibular disease? Vestibular diseases are common in dogs and cats and may result in any combination of the following clinical signs: head tilt, falling, leaning, rolling, circling, nystagmus, strabismus, and ataxia. Vomiting can also be seen with acute vestibular disorders. Head Tilt: A head tilt commonly occurs with vestibular disease and is usually towards the side of the problem. It is an abnormal head posture characterized by a rotation of the head due to a loss of antigravity muscle tone on one side of the neck. A head tilt must be differentiated from a head turn (torticollis) in where the median plane of the head remains perpendicular to the ground, but the nose is turned to one side. A head turn is not associated with a vestibular disorder but can occur with forebrain and brainstem diseases. Circling: Can occur with either a vestibular disease or with a focal forebrain disease. Animals usually circle toward the side of the problem. Tight circles are usually seen with vestibular diseases, while wide circles (almost pacing) are often associated with forebrain diseases. Nystagmus: This is involuntary, rhythmic oscillations of the eyeballs. There are two types of nystagmus - physiologic and pathologic. Physiologic nystagmus occurs in normal animals while pathologic nystagmus occurs with vestibular disease. Physiologic nystagmus can be induced in a normal animal by turning the head side to side (also know as the vestibulo-ocular reflex). It is characterized by a slow phase in the opposite direction of the head movement and a fast phase (compensatory phase) in the same direction of the head movement. The direction of the nystagmus is defined in the direction of the fast phase which is typically away from the side of the problem. Physiologic nystagmus can be decreased or absent in animals with vestibular disorders. Pathologic nystagmus occurs with vestibular disease and can be either spontaneous or

2 positional. Spontaneous nystagmus is observed when the head is in a normal position at rest. Positional nystagmus occurs when head position is altered; it can often be seen by placing the animal upside down on its back. Nystagmus is classified by its direction (horizontal, rotary, or vertical) and may change direction when head position is changed. Strabismus: This refers to an abnormal position of the globes. Strabismus is usually detected when the head is placed in an abnormal position (dorsally extending the head or placing the animal on its back) and is present on the side of the problem. Ventral or ventrolateral strabismus is usually seen in the eye on the same side as the vestibular disease. Ataxia: This is defined as an uncoordinated gait and can be seen with vestibular disease (vestibular ataxia), cerebellar disease (cerebellar ataxia), or a problem in the spinal cord or brainstem (proprioceptive or sensory ataxia). Ataxia seen with vestibular disease is characterized by swaying of the head and trunk, base-wide stance, leaning, falling, and rolling to side of the lesion. Bilateral vestibular lesions usually cause wide excursions of the head from side to side. 2. How do you determine if a patient has a peripheral or central vestibular disease? The vestibular system consists of two components on each side of the body - the peripheral component and the central component. Clinical signs of vestibular disease can result from a lesion in one of the components. The peripheral component consists of receptor organs in each inner ear and the vestibular portion of each cranial nerve eight which courses through the petrous temporal bone. The central component consists of vestibular nuclei in the brainstem and parts of the cerebellum. When assessing a patient with vestibular signs, the first step is to localize the problem to the right or left side of the body, then localize it to the peripheral or central component of the vestibular system. Localizing the vestibular signs is important because it will help determine potential causes and the necessary diagnostics. Peripheral and central vestibular diseases can cause a head tilt, horizontal or rotary nystagmus, and ataxia. These signs are usually ipsilateral (same side) to the side of the lesion. Peripheral Vestibular Disease (PVD) Postural reaction deficits are not seen with PVD. Facial paralysis (cranial nerve 7) and Horner s syndrome (sympathetic innervation to the eye) may also be present on the same same as the PVD because of the proximity of these nerves to the peripheral vestibular components in the inner ear. A resting nystagmus rate 66 beats per is more likely to be seen with peripheral vestibular disease. With bilateral PVD, nystagmus and head tilt will often not be present. Affected animals will walk crouched and may have wide, side-to-side excursions of the head. Central Vestibular Disease (CVD) Postural reaction deficits are the the strongest indication of CVD. Postural reaction deficits occur because the sensory and motor pathways that control these reactions are located in the brainstem near the vestibular nuclei. The deficits are on the same side as the CVD. Other

3 important features of CVD are vertical nystagmus and positional nystagmus (nystagmus that changes direction on changing head position). The presence of cranial nerve deficits other than facial (7) or vestibulocochlear (8) is suggestive of a central lesion. Alterations of consciousness of mental status may also support a CVD. The following table can be used to help differentiate a PVD versus CVD based on the clinical signs. PVD CVD Head tilt (ipsilateral) (ipsilateral; may be contralateral with paradoxical disease) Ataxia (ipsilateral) (ipsilateral) Nystagmus Horizontal Rotary Vertical Positional NO Rarely YES Postural reaction deficits NO YES (ipsilateral) Circling (ipsilateral) (either way) Facial paralysis YES (ipsilateral) Uncommon Horner s syndrome YES (ipsilateral) Uncommon Once a lesion has been localized to the peripheral or central vestibular component on one side of the body, a differential list and necessary diagnostics can be determined. 3. What is Paradoxical Vestibular Disease? Paradoxical Vestibular Disease is a specific CVD that occurs with a lesion in the caudal cerebellar peduncles or flocculonodular lobes of the cerebellum, which results in a head tilt that is away from the side with the lesion. The patient may also circle away from the side with the lesion. Another unique feature of this disease is the fast phase of the nystagmus will be towards the side with the lesion. The key to localizing which side of the cerebellum has a lesion is to determine which side has proprioceptive deficits. The postural reaction deficits will be on the same side as the lesion, while the head tilt will be in the opposite direction. The most common causes of Paradoxical Vestibular Disease include a tumor, an infarction, and an inflammatory disease.

4 4. What are the most common peripheral vestibular diseases? The most common PVDs include otitis media/interna, idiopathic vestibular syndrome, ototoxic drugs, and hypothyroidism. Oropharyngeal polyps in cats can also cause peripheral vestibular disease. Otitis media/interna is the most common cause of PVD in both dogs and cats. This is usually secondary to otitis externa that has progressed into the middle and inner ear. Otitis media/interna can also be caused by a retrograde infection via the eustachian tube or by hematogenous spread. The absence of otitis externa on otoscopic exam does not eliminate the presence of an otitis media/interna. Facial paralysis and Horner s syndrome may be seen. Diagnostics include an otoscopic exam and imaging studies (bulla radiographs, CT, and MRI). If there is fluid in the middle ear, a sample should be obtained via myringotomy for culture and cytology. Treatment consists of systemic antibiotics for a minimum of 6-8 weeks. Surgical drainage via bulla osteotomy should be considered if medical treatments fails. The prognosis for recovery is fair because the head tilt and facial paralysis usually persist. Idiopathic vestibular disease occurs in both dogs (usually geriatric) and cats (any age). The clinical signs are typically peracute and most animals can be quite debilitated for the first hours. Facial paralysis and Horner s syndrome are not seen with this disease, so if present, other differentials should be considered. The diagnosis is usually based on the signalment, history, neurologic exam, and exclusion of other PVDs. Most affected animals will significantly improve within 72 hours and will be back to normal in 2-4 weeks. The head tilt is typically the last neurologic signs to improve and may be permanent. Treatment is supportive and symptomatic. Meclizine may help decrease nausea. Recurrence is uncommon. Ototoxic drugs administered orally or topically can cause PVD and deafness. These drugs damage the vestibular receptors in the inner ear. Oral aminoglycoside antibiotics and earcleaning solutions are most frequently incriminated. Toxicity usually occurs when these drugs are used at higher doses, when treatment is greater than 2 weeks, or the patient has impaired renal function. Topical agents should never be introduced into the ear when the tympanic membrane cannot be visualized or is ruptured because of the potential for ototoxicity. A diagnosis is usually based on the development of vestibular signs with a recent history of ototoxic drug administration. There is no definitive treatment. The ototoxic drug should be stopped immediately. Vestibular signs usually improve over time but deafness may be permanent. Hypothyroidism has been associated with both PVD and CVD, but is more often associated with PVD. The exact cause for the peripheral disease is unknown, but decreased axonal transport and Schwann cell dysfunction have been implicated. The cause for central vestibular disease may be related to ischemic infarction or hyperviscosity-associated hyperlipedemia. Diagnosis is based on documentation of hypothyroidism and exclusion of other disease processes. Treatment consists of thyroid hormone supplementation. Generally, dogs with PVD respond well to treatment. Resolution of neurologic signs may take weeks or months with a head tilt often

5 persisting. Dogs with CVD may not respond as well depending on the presence of a brain infarction. 5. What are the most common central vestibular diseases? The most common CVDs include encephalitis, brain tumors, vascular infarctions, and metronidazole toxicity. Encephalitis is probably the most common cause of CVD. Although encephalitis can occur in any breed, it occurs most commonly in young to middle-aged, small breed dogs. Autoimmune diseases (GME, necrotizing encephalitis) and infectious diseases (distemper, RMSF, E. canis, FIP, Toxoplasmosis) are the main causes of encephalitis. A diagnosis is based on the history, signalment, clinical signs, MRI findings (multifocal contrast enhancing lesions), cerebrospinal fluid analysis, and infectious disease titers. Autoimmune encephalitis is treated with immunomodulatory drugs. Corticosteroids are traditionally given as the primary treatment; however, other immunomodulatory drugs (azathioprine, cytosine arabinoside, cyclosporine) which have traditionally been used as an add-on therapy to corticosteroids are starting to be used more often as the primary treatment. The prognosis for autoimmune encephalitis is guarded as animals may live weeks to years. Treatment for infectious encephalitis is based on the cause and the prognosis varies. Brain tumors in the caudal fossa are a common cause of CVD in dogs older than 5 years of age. Tumors in this location affect the vestibular nuclei in the brainstem and the vestibular portions of the cerebellum. Meningiomas and choroid plexus tumors are the most common tumors that occur in the caudal fossa. Clinical signs are often slowly progressive. A presumptive diagnosis is made by advanced imaging (CT or MRI) and is confirmed with histopathology. Treatment and prognosis depend on the location and tumor type. Surgical approaches to the caudal fossa can be difficult and may limit surgery as a treatment option. Radiation therapy may be used to treat primary intracranial tumors when surgery is not a treatment option. The median survival times vary with treatment, tumor type and location. Vascular infarctions can occur in the brainstem or cerebellum resulting in CVD, although they are more likely to occur in the cerebellum. They are more common in dogs than cats. Neurologic signs are acute and nonprogressive. MRI and spinal fluid analysis are needed to exclude other CVDs and make a presumptive diagnosis. There is no definitive treatment; however, animals usually improve within 5-7 days and may completely recover. Further evaluation for renal disease, hyperadrenocorticism, hypothyroidism, hypertension, pheochromocytoma, and diseases that may predispose for vasculitis and thrombosis should be considered. Metronidazole is commonly used to treat a variety of conditions in dogs and cats. CVD has been reported to occur in animals taking dosages >60 mg/kg/day for 7-12 days but signs can occur in animals taking lower dosages. A presumptive diagnosis is based upon neurologic signs and a history of metronidazole administration. Clinical signs usually resolve 1-2 weeks after

6 discontinuing the drug. Diazepam administration in dogs can shorten the recovery time to 3 days (0.43 mg/kg orally or IV every 8 hours for 3 days). Vestibular Diseases Disease PVD CVD Degenerative Uncommon Uncommon Anomalous Congenital Chiari-like malformation, Intracranial cyst, Dandy-Walker syndrome Metabolic Hypothyroidism Hypothyroidism (rare) Neoplastic Middle/inner ear tumor Primary or metastatic tumor Nutritional Inflammatory/Infectious Idiopathic Toxic Otitis media/interna Nasopharyngeal polyp Idiopathic vestibular disease Aminoglycoside antibiotics Chlorhexidene flush Iodophors flush Thiamine deficiency Autoimmnune encephalitis (GME, necrotizing) Infectious encephalitis (Distemper, Toxoplasma, Neospora, FIP, Fungal) Metronidazole Trauma Head trauma Head trauma Vascular Infarction Hemorrhage 6. What tests can be done in a general practice for a patient that has vestibular disease? The minimum data base for all patients with vestibular signs should include a complete blood count, biochemistry profile, thyroid testing, urinalysis, otoscopic exam, and pharyngeal exam. Peripheral Vestibular Disease The diagnostic plan for patients with PVD includes a thorough otoscopic exam and imaging of the tympanic bulla radiographs. These tests should be done under sedation or general anesthesia. A thorough examination of the external ear canal can be performed with a hand-held otoscope or video-otoscopy. Middle ear pathology should be suspected if the tympanic membrane is ruptured, bulging, or cloudy. While diseases affecting the external canal may be visualized, the presence of an intact tympanic membrane does not eliminate the possibility of a middle ear disease. If the tympanic membrane is ruptured, a culture can be taken from the middle ear cavity. If the tympanic membrane is intact, a myringotomy can be performed to obtain a culture.

7 Radiographs of the tympanic bulla require general anesthesia to allow for adequate positioning. Five conventional radiographic views are needed to investigate the osseous bulla: dorsoventral, lateral, open-mouth, and a right and left 20 lateral oblique views. Although positive radiographs can diagnose middle ear disease, negative radiographs do not rule out the presence of middle ear disease. Radiographic evaluation of animals with vestibular disease is not typically performed because of the complexity of the anatomy of the head, superimposition of structures, and the lack of specificity associated with radiographic findings. Computed tomography and MRI are more sensitive than radiographs in diagnosing middle ear disease. Thoracic radiographic should be obtained in older animals to exclude systemic diseases that may have spread to the nervous system (i.e. fungal disease or metastatic neoplasia). Similarly, in animals exhibiting clinical signs referable to the abdominal cavity, radiographic or ultrasonographic examination of the abdomen should be performed. Identifying an underlying systemic disease through noninvasive imaging technique may provide a presumptive diagnosis for vestibular dysfunction, thereby eliminating unnecessary risk to the animal and expense to owners. Central Vestibular Disease In addition to the minimum database, the diagnostic workup for patients suspected of having CVD includes advanced imaging (computed tomography or MRI), cerebrospinal fluid analysis (CSF), and serum/csf titers for various organisms. Additional testing would be based on the presumptive diagnosis. Brain tumor (biopsy, investigate for metastatic disease) Cerebrovascular accident (clotting profile, blood pressure, cardiac evaluation, adrenal testing) 7. When should I refer a patient with vestibular disease to a neurologist? Any patient that has neurologic deficits consistent with CVD should be referred to a neurologist for further evaluation. These include postural reaction deficits and vertical nystagmus. If either of these are present, the patient should be referred. Patients with otitis media/interna that are not responding to therapy should also be referred for further evaluation. Patients suspected of having idiopathic disease that do not improve or develop other neurologic deficits should be referred. Referral should also be recommended for any patient that has intermittent vestibular signs. 8. What is the prognosis for vestibular disease? The prognosis for vestibular disease depends on the cause. The one thing to stress to clients when discussing prognosis is that regardless of the cause, the head tilt is often the last neurologic sign to improve and is often permanent. This does not interfere with the animal s quality of life and is not debilitating.

8 9. I have a patient with CVD. The client doesn t have money for an MRI. What can I do? When a client does not have money for diagnostics, empirical treatment for the most common CVDs can be initiated. The minimum diagnostic database (bloodwork, thoracic radiographs, urinalysis, complete thyroid panel) should be done prior to starting empirical treatment. Empirical Treatment Dose Rationale Prednisone 1 mg/kg PO BID tapering dose Inflammatory disease Peritumoral edema Clindamycin 10 mg/kg PO TID x 28 days Toxoplasmosis infection Neosporosis infection Doxycycline or Minocycline 10 mg/kg PO BID x 28 days E. canis RMSF Meclizine Cerenia 25 mg PO SID (dogs) 12.5 mg PO SID (cats) 1mg/kg SC q 24hrs up to five days 8 mg/kg PO q 24hrs x 2 consecutive days Reduce nausea Stop vomiting 10. Are there any drugs other than Meclizine (Antivert) that treat nausea? Diphenhydramine (Benadryl) or Dimenhydrinate (Dramamine) can be used to help treat motion sickness and nausea that can occur with vestibular disease. The exact mechanism of how these drugs interact with the vestibular system and vomiting center is not known. Drug Diphenhydramine (Benadryl) Dimenhydrinate (Dramamine) Dose 2-4 mg/kg PO TID 4-8 mg/kg PO TID