Noice induced hearing loss, Ototoxic drugs, Meniers disease, Rotataory vertigo, Sensorineural hearing loss, Tinnitis, Infections, Acoustic neuroma,

Transcription

1 Disorders of hearing and balance LEARNING OBJECTIVE At the end of lecture student must be able to know, Hearing disorders, Types of hearing disorders, Functional classification, Causes, Middle ear disorders, Cholestoma, Sensorineural disorders, Noice induced hearing loss, Ototoxic drugs, Meniers disease, Rotataory vertigo, Sensorineural hearing loss, Tinnitis, Infections, Acoustic neuroma, Hereditory causes. HEARING DISORDERS The most common hearing disorders are those that affect hearing sensitivity. When a sound is presented to a listener with a hearing sensitivity disorder, one of 2 things may occur: The listener with a HS disorder may be unable to detect the sound. The sound will not be as loud to that listener as it would be to a listener with normal hearing. Hearing Abnormalities Deafness is usually divided into two types: (1) that caused by impairment of the cochlea or impairment of the auditory nerve, which

2 is usually classified as nerve deafness. (2) that caused by impairment of the physical structures of the ear that conduct sound itself to the cochlea, which is usually called conduction deafness. Types of Hearing Disorders Many ways to classify hearing disorders 1. Nature of the loss: Sensitivity vs. Acuity Dysacusia Deficit in discrimination or interpretation of sound. Acuity deficits sometimes due to disorders of the central auditory system. Disorders of sensitivity and acuity are not mutually exclusive. Functional Classification Conductive Disorders involving the conduction of sound to the cochlea. Sensori-neural Disorders involving the cochlea (usually the hair cells) or 8 th N. Central Disorders affecting the brain stem or auditory cortex. Two related terms: Peripheral Not central; i.e., conductive or sensorineural. Retrocochlear Disorders involving anatomical structures beyond the cochlea; i.e., 8 th N, brain stem, auditory cortex. Cause or Etiology of the Disorder Hearing disorders can be classified on the basis of the cause of the disorder. Some examples: Ototoxic drugs Noise exposure Old age (presbycusis)

3 Otitis media 8 th N tumors Meniere s Disease In this review, we will proceed by functional subsystem (conductive, sensori-neural, central), and by etiology within each subsystem. Conductive Hearing Disorders Congenital malformations. There are many of these. Most serious is congenital atresia collapse or closure of the EAM (ear canal). May occur in isolation, but typically associated congenital malformations of the middle ear as well. Impacted wax (cerumen) results in mild hearing loss. easily treated by removal of the wax. Middle Ear DISORDERS Otitis Media By far the most common cause of conductive hearing loss. By far the most common health problem in children. Otitis media means inflammation of the middle ear. Disease Process OM involves a very specific chain of events revolving around the abnormal functioning of the Eustachian tube. Begins with an ordinary upper respiratory infection (head cold) involving, among other things, the nasopharynx. Nasal secretions infect the Eustachian tube. The Eustachian tube, which is normally closed, becomes inflamed and can no longer open upon swallowing, yawning, etc. This means that pressure can no longer be equalized between the middle ear and the ambient air. Middle Ear DISORDERS

4 Oxygen in the ME cavity is consumed by ordinary metabolic processes. Ordinarily, this oxygen is re-supplied through the Eustachian tube. With a plugged ET, this cannot occur. The absorption of oxygen without re-supply results in a partial vacuum (i.e., lower than normal pressure) in the ME. The pressure drop sucks the TM inward into the ossicular chain, reducing its mobility. Consequences: hearing loss and pain often quite intense. Partial vacuum creates another problem: Recall that the entire ME cavity is lined with mucous membrane. The pressure drop causes clear fluid to be sucked out of the mucosal lining of the ME. This accumulation of fluid contributes to the conductive hearing loss. Condition is called serous otitis media or nonsuppurative otitis media. Defining features: (1) clear, thin, watery fluid, (2) fluid is sterile (not infected). Suppurative or Purulent Otitis Media: As the disease progresses, the fluid can become infected and thickens into (eck) pus. Middle Ear DISORDERS The major consequences of OM are hearing loss and pain. The hearing loss is typically mild (usually db) and often fluctuating. The pain varies quite a bit but is often quite severe. It is not unusual for the pressure drop in the ME to become severe enough to cause the TM to rupture. Some Additional Terminology Acute vs. Chronic OM: A specific bout of OM with pain, accumulation of fluid, etc., is called acute otitis media. If OM lasts more than 2-3 months, the condition is known as chronic otitis media. Recurrent OM: Frequent bouts of OM: OM is treated successfully, then returns, then treated, then returns This gets old after a while but is pretty common. A Few Additional Terms Otitis Media with Effusion (OME): Otitis media characterized by the accumulation of fluid. Mucoid or Mucous Otitis Media ( Glue Ear ): Fluid in middle ear is thick and gooey rather than thin and watery. Hearing loss is often more severe than serous OM. Seen in some cases of recurrent OM purulent OM is treated, killing the infection, but fluid does not drain.

5 Speech and Language Delay?? Evidence is mixed and controversial, but there is some research suggesting that frequent bouts of OM can result in delays in acquiring speech and language. Surprising to some since hearing loss is relatively mild and fluctuating, with significant periods of normal hearing in between bouts of OM for most kids. But, there is also evidence from other sources indicating that kids need higher sound levels to understand speech with the same accuracy as adults. A Few Additional Terms Otosclerosis Begins as a soft, spongy growth of new bone may appear anywhere in the ME, but most often near oval window. Later hardens (i.e., becomes sclerotic) In 90% of cases: No symptoms In unlucky 10%: Growth reduces mobility of stapes, causing a conductive HL. Progressive. Beginning in childhood. For that unlucky 10%, HL typically begins in late teens, early 20s. Maximum HL seldom worse than ~50-60 db. Treatment: Stepedectomy (removal of stapes and replacement with an artificial stapes) Cholesteatoma Cyst that invades the ME Usually grows rapidly Can: (1) destroy the ossicular chain, (2) invade the cochlea, (3) break through the thin shelf of bone that forms the superior surface of the ME

6 cavity, invading the meninges. HL usually mild and not really the major concern. Cholesteatoma Cholesteatomas are benign growths of skin in the middle ear and mastoid. These "skin cysts" can and do cause many problems in the ear. Cholesteatomas commonly cause hearing loss and infections. The only treatment available to cure a cholesteatoma is surgery. The surgery that is typically performed is tympanoplasty with or without mastoidectomy. Cholesteatomas left untreated can go on to cause serious and sometimes life threatening health problems, such as meningitis or brain abscess. Cholesteatomas can develop in both children and adults. Surgery is usually done as day surgery (outpatient). Sensori-Neural Hearing Loss General: By far the most common underlying cause of SN HL is damage to the hair cell transducers. In these most common cases, the auditory nerve and central auditory pathway are intact, but stimulation of the auditory nerve is abnormal due to damaged hair cells. There are many possible reasons for the hair cells to become damaged. The various etiologies of SN HL consist mainly of a catalog of different causes of hair cell damage. Presbycusis Hearing loss associated with aging Most common cause of SN HL and most common cause of HL overall. Noise-Induced Hearing Loss Exposure to high levels of noise can damage HCs and cause SN HL. Two types: Acoustic trauma: Injury due to brief exposure to very intense sounds such as gun shots, artillery fire, explosions, etc. HL may be severe and permanent, but substantial recovery is common.

7 Long-term noise exposure (more common): Damage results from long-term exposure to high levels of noise. Common in some occupational settings heavy manufacturing and agriculture being the most common. Amount of inner-ear damage depends on the combination of: Intensity of the noise Length of exposure Ototoxic Drugs Certain drugs can cause SN HL. Toxicity effects vary from mild and temporary to severe and permanent. Some very common drugs such as aspirin (especially in large doses) can cause hearing loss (and/or tinnitus), but not in most people, and the loss is typically mild and temporary. An especially important group of antibiotics are notoriously ototoxic. Examples include neomycin, streptomycin, kanamycin. Since this is well known, why might these drugs ever be administered? Ototoxic Drugs Antibiotics Salicylates Non-Steroidal Anti-Inflammatory Drugs (NSAIDS) Neomycin Erythromycin Quinine Vancomycin Diuretics Chemotherapeutic Agents Quinine Mucosal Protectant

8 Meniere s Disease Serious, often debilitating disease of hearing and balance of unknown/uncertain cause. MD affects a single ear in about 75% of cases. Four major symptoms: Periodic episodes of rotary vertigo (the sensation of spinning) or dizziness (the Meniere s attack ) Fluctuating, progressive, low-frequency hearing loss Tinnitus A sensation of "fullness" or pressure in the ear Cause of Meniere s The proximate (i.e., immediate) cause of MD is excessive and fluctuating pressure in the endolymphatic fluid that courses through the membranous labyrinth of the cochlea and vestibular systems. This causes the membranous labyrinth to balloon or dilate. Condition is known as endolymphatic hydrops. Result is progressive damage to the hair cells responsible for both hearing and balance. Underlying cause of the fluid imbalance not known for sure. Likely suspects viral infection or autoimmune disorder affecting production or absorption of endolymph (duh). Rotary Vertigo This is easily the most disruptive and debilitating symptom of Meniere s. Similar to the mild vertigo you get from too many beers, or that you may remember as a kid from spinning around on a playground. Some major differences: Dramatically more severe Often accompanied by nausea, vomiting, sweating Onset is usually sudden Typically persists for hours or even days

9 Patient has little or no ability to control it Condition often leaves the patient confined to a bed and as stationary as possible for long periods of time, until the symptoms subside. Even small head movements can greatly exacerbate the symptoms SN Hearing Loss Fluctuating Initially affects low-frequencies more than highs, but may spread to highs as the disease progresses Progressive (i.e., gets worse with time) Hearing may be completely lost in the affected ear Usually unilateral Sounds may appear tinny or distorted Loudness intolerance is common (abnormal sensitivity to intense sounds) Tinnitus Ringing, roaring, or buzzing sensation Fluctuates in intensity but does not abate Pretty annoying Infections Bacterial or viral infections that invade the inner ear can cause SN HL and disruptions of vestibular function. Generic term for infections that invade the inner ear: labyrinthitis. Meningitis can sometimes spread to the inner ear and result in labyrinthitis. Other infectious diseases: Mumps, measles, meningitis, encephalitis, chicken pox, influenza, and syphilis can also invade the inner ear and cause SN HL and/or vestibular symptoms.

10 acoustic neuroma Benign tumor that exerts pressure on 8 th N Almost always slow growing Most common symptom: hearing loss (mild initially), often accompanied by tinnitus Vestibular problems may also occur Cause is unknown Continued tumor growth can be life threatening Treatment: Surgical removal or radiation Early detection is really important: Small tumors can be removed with less risk of destroying the 8 th N (and sometimes the 7 th N as well). Early diagnosis is tough early-stage symptoms are un-dramatic Hereditary Causes Two patterns: autosomal dominant One parent has a dominant gene for SN HL (and typically has a hearing loss). There is at least a 50% probability that the child will also have a hearing loss. Probability is higher if both parents have the dominant gene. autosomal recessive Both parents (typically with normal hearing) carry a recessive gene for SN HL. Each child will have a 1 in 4 chance of inheriting the bum gene.