Chapter 030. Disorders of Smell, Taste, and Hearing (Part 10)

Presbycusis (age-associated hearing loss) is the most common cause of sensorineural hearing loss in adults. In the early stages, it is characterized by symmetric, gentle to sharply sloping high-frequency hearing loss. With progression, the hearing loss involves all frequencies.More importantly, the hearing impairment is associated with significant loss in clarity. There is a loss of discrimination for phonemes, recruitment (abnormal growth of loudness), and particular difficulty in understanding speech in noisy environments.Hearing aids may provide limited rehabilitation once the word recognition score deteriorates below 50%. Cochlear implants are the treatment of choice when hearing aids prove inadequate, even when...
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Chapter 030. Disorders of Smell, Taste, and Hearing (Part 10) Chapter 030. Disorders of Smell, Taste, and Hearing (Part 10) Presbycusis (age-associated hearing loss) is the most common cause ofsensorineural hearing loss in adults. In the early stages, it is characterized bysymmetric, gentle to sharply sloping high-frequency hearing loss. Withprogression, the hearing loss involves all frequencies. More importantly, the hearing impairment is associated with significantloss in clarity. There is a loss of discrimination for phonemes, recruitment(abnormal growth of loudness), and particular difficulty in understanding speechin noisy environments. Hearing aids may provide limited rehabilitation once the word recognitionscore deteriorates below 50%. Cochlear implants are the treatment of choice whenhearing aids prove inadequate, even when hearing loss is incomplete. Ménières disease is characterized by episodic vertigo, fluctuatingsensorineural hearing loss, tinnitus, and aural fullness. Tinnitus and/or deafnessmay be absent during the initial attacks of vertigo, but invariably appear as thedisease progresses and increase in severity during acute attacks. The annual incidence of Ménières disease is 0.5–7.5 per 1000; onset ismost frequently in the fifth decade of life but may also occur in young adults orthe elderly. Histologically, there is distention of the endolymphatic system(endolymphatic hydrops) leading to degeneration of vestibular and cochlear haircells. This may result from endolymphatic sac dysfunction secondary toinfection, trauma, autoimmune disease, inflammatory causes, or tumor; anidiopathic etiology constitutes the largest category and is most accurately referredto as Ménières disease. Although any pattern of hearing loss can be observed, typically, low-frequency, unilateral sensorineural hearing impairment is present. MRI should beobtained to exclude retrocochlear pathology such as a cerebellopontine angletumor or demyelinating disorder. Therapy is directed towards the control of vertigo. A low-salt diet is themainstay of treatment for control of rotatory vertigo. Diuretics, a short course ofglucocorticoids, and intratympanic gentamicin may also be useful adjuncts inrecalcitrant cases. Surgical therapy of vertigo is reserved for unresponsive casesand includes endolymphatic sac decompression, labyrinthectomy, and vestibularnerve section. Both labyrinthectomy and vestibular nerve section abolish rotatory vertigoin >90% of cases. Unfortunately, there is no effective therapy for hearing loss,tinnitus, or aural fullness from Ménières disease. Sensorineural hearing loss may also result from any neoplastic, vascular,demyelinating, infectious, or degenerative disease or trauma affecting the centralauditory pathways. HIV leads to both peripheral and central auditory systempathology and is associated with sensorineural hearing impairment. A finding of conductive and sensory hearing loss in combination is termedmixed hearing loss. Mixed hearing losses are due to pathology of both the middleand inner ear, as can occur in otosclerosis involving the ossicles and the cochlea,head trauma, chronic otitis media, cholesteatoma, middle ear tumors, and someinner ear malformations. Trauma resulting in temporal bone fractures may be associated withconductive, sensorineural, or mixed hearing loss. If the fracture spares the innerear, there may simply be conductive hearing loss due to rupture of the tympanicmembrane or disruption of the ossicular chain. These abnormalities can be surgically corrected. Profound hearing loss andsevere vertigo are associated with temporal bone fractures involving the inner ear. A perilymphatic fistula associated with leakage of inner-ear fluid into themiddle ear can occur and may require surgical repair. An associated facial nerveinjury is not uncommon. CT is best suited to assess fracture of the traumatizedtemporal bone, evaluate the ear canal, and determine the integrity of the ossicularchain and the involvement of the inner ear. CSF leaks that accompany temporalbone fractures are usually self-limited; the value of prophylactic antibiotics isuncertain. Tinnitus is defined as the perception of a sound when there is no sound inthe environment. It may have a buzzing, roaring, or ringing quality and may bepulsatile (synchronous with the heartbeat). Tinnitus is often associated with either a conductive or sensorineuralhearing loss. The pathophysiology of tinnitus is not well understood. The cause ofthe tinnitus can usually be determined by finding the cause of the associatedhearing loss. Tinnitus may be the first sympt ...