Goroll_Primary Care Medicine, 8e

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Chapter 212 Evaluation of Hearing Loss

Sensorineural Hearing Loss Sensorineural loss arises from dysfunction of the cochlear sensorineural elements and/or of the cochlear nerve. Patients may complain that they can hear people speaking but have difficulty deciphering words because speech discrimination is poor. Shouting may only exacerbate the problem. The patient with high-frequency loss may have difficulty hearing doorbells, telephones, fire alarms, or a ticking watch and may note more difficulty in hearing the higher-pitched female or child’s voice. Recruitment—an abnormally rapid increase in perceived loud ness with increased sound intensity—may be present and indi cates cochlear dysfunction. With Rinne testing, air conduction is perceived better than bone conduction. Tinnitus of varying degrees and intensity is often a concomitant complaint. Presbycusis Presbycusis is hearing loss associated with aging and is the most common cause of diminished hearing in the elderly. There are four types of presbycusis, distinguished according to the cor related pathologic changes in the cochlea. Hair cell loss and cochlear neuron degeneration are the most widely recognized changes. The hearing loss is bilaterally symmetric and gradual in onset. Most cases begin with a loss of the high frequencies with slow progression. Eventually, middle- and low-frequency sounds also become difficult to perceive (Figs. 212-1 and 212-2). Noise-Induced Hearing Loss Noise-induced hearing loss is of major epidemiologic and eco nomic significance. Chronic exposure to sound levels in excess of 85 to 90 dB causes hearing loss, particularly in the frequency range around 4,000 Hz. The patient may be unaware of the prob lem because the speech frequencies (500 to 4,000 Hz) are initially unaffected. At first, there may be a temporary threshold shift in which there is a reversible elevation in the threshold for sound perception. The ear may feel full, or the patient may complain of a sense of pressure. If loud noise exposure ceases at this point, hearing returns to its previous level. If exposure persists, however, a permanent threshold shift ensues. The term acoustic trauma more specifically relates to a particular single noise event (e.g., a shotgun blast) that induces an immediate irreversible hearing loss. Drug-Induced Hearing Loss The aminoglycoside antibiotics, such as gentamicin, are rep resentative of ototoxic drugs. An early sign of gentamicin oto toxicity is disequilibrium. Monitoring antibiotic blood levels is

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Hearing Loss (dB)

FIGURE 212-2 Late presbycusis due to loss of cochlear neurons. Note poor discrimination. DISCRIM, discrimination; × , left ear, air; O, right ear, air; < , right ear, bone; R, right; L, left.

the best, but not perfect, way to avoid such problems, adjusting dose according to peak serum levels. Restricting dosing to once daily and duration of therapy to less than 1 week also helps to reduce risk. Other potentially ototoxic drugs, including those causing symmetric sensorineural hearing loss, include furose mide, ethacrynic acid, cisplatin, quinidine, and aspirin. Aspirin doses averaging 6 to 8 g/d predictably cause tinnitus and com pletely reversible hearing impairment. Ménière Disease Ménière disease manifests most commonly with a unilateral, fluctuating, low-frequency, sensorineural hearing loss, usu ally associated with tinnitus, a sensation of fullness in the ear, and intermittent episodes of vertigo each lasting hours to 1 to 2 days. Vertigo may be the presenting symptom of Ménière disease, with later onset of fluctuating hearing loss. Progression of hearing loss may occur, eventually encompassing the higher frequencies as well. Acoustic Neuromas Acoustic neuromas—benign tumors of the eighth cranial nerve—are rare but important considerations in the evaluation of asymmetric sensorineural hearing loss, often in conjunction with disequilibrium (see Chapter 166). Speech discrimination is much worse than predicted by the pure-tone hearing loss. Symptoms progress in relentless progressive fashion. Sudden Sensorineural Hearing Loss Sudden sensorineural hearing loss (defined as occurring over no more than a 72-hour period with a subjective sensation of hear ing impairment in one or both ears) can appear with or without obvious cause or warning. Often the cause is not evident even after assessment, but schwannoma (acoustic neuroma), stroke, and malignancy need to be ruled out in cases of sudden uni lateral hearing loss. Cases without evident cause after workup are designated idiopathic sudden sensorineural hearing loss . The etiology of the idiopathic variant is a matter of debate, but viral infection and vascular insufficiency are among the postulated mechanisms. Men and women are equally affected, with fre quency greatest between ages 43 and 53. Up to half present with transient vestibular symptoms. Recovery correlates with pattern of hearing loss, age ( > 40 years or < 40 years), presence or absence of vertigo (those without vertigo fare better), and electronystagmogram pattern. Over a third of patients recover spontaneously and some may never come for care.

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Hearing Loss (dB)

FIGURE 212-1 Presbycusis due to hair cell loss. Note the good hearing thresholds at the speech frequencies of 250 to 2,000 Hz. DISCRIM, discrimi nation; × , left ear, air; O, right ear, air; < , right ear, bone; R, right; L, left.