Goroll_Primary Care Medicine, 8e

Chapter 212

EVALUATION OF HEARING LOSS NEIL BHATTACHARYYA

F rom studies of patient-reported hearing, it is estimated that more than 16% of the population of the United States has a hearing problem. Although hearing loss on an age-adjusted basis is less prevalent due to less manufacturing work-related noise trauma, prevalence of age-related hearing loss is increas ing with the aging of the population. The problem is par ticularly problematic among the elderly, capable of impairing quality of life and increasing risk of dementia. People with seriously impaired hearing often become withdrawn or appear confused. Those with subtle hearing loss may go unrecognized. Many can be helped, especially those with a conductive prob lem but also increasingly among those having sensorineural hearing loss. The primary physician has the opportunity to screen for and detect hearing loss, to search for an etiology, and to decide when referral to an otolaryngologist is indicated.

Conductive Hearing Loss Conductive loss presents with diminished perception of sound, particularly for low-frequency tones and vowels. There is often a history of previous ear disease. In the Weber test, a tuning fork placed against the frontal bone or the maxillary incisors is perceived more loudly in the ear with a conductive hearing loss. The Rinne test shows that bone conduction is better than air conduction. Obstruction of the auditory canal by severely impacted cerumen, a foreign body, exostoses, external otitis, oti tis media with effusion, or scarring or perforation of the drum due to chronic otitis may be responsible for the conductive loss. Otosclerosis Otosclerosis, a surgically remediable cause of conductive hear ing loss, is a disorder of the bony labyrinth that fixes the foot plate of the stapes in the oval window. Clinical otosclerosis has an estimated prevalence of about 1% among whites and 0.1% among blacks. Two thirds of the cases are seen in women. There appears to be an association between pregnancy and progres sion of otosclerotic hearing loss. The condition is believed to be inherited in an autosomal dominant fashion, with varying clinical expressivity. It generally presents in the second or third decade of life. Exostoses Exostoses are bony excrescences of the external auditory canal. They are characteristically located in the anterior, posterior, and superior quadrants of the canal. Nearly always bilaterally symmetric, their occurrence seems to be related to repetitive exposure to cold water (e.g., as in ocean swimming). They can cause symptoms by blockage of the external auditory canal, resulting in conductive hearing loss, or by sequestration of debris and cerumen with subsequent infection. Glomus Tumors Glomus tumors or paragangliomas are rare benign, highly vascular tumors derived from normally occurring glomus formations of the middle ear and the jugular bulb. Present ing symptoms include conductive hearing loss (from middle ear mass effect), spontaneous hemorrhage from the canal, and paralysis of the 9th, 10th, and 11th cranial nerves (the jugular foramen syndrome). Pulsatile tinnitus should raise suspicion for a glomus tumor. With progression, it may involve the intra cranial space or cause bony destruction of the base of the skull. Otitis Media with Effusion Chronic otitis media with effusion is a rare diagnosis in adults. Causes include nasopharyngeal masses, viral upper respiratory infection, allergy, and, rarely, autoimmune conditions. Ninety percent of adult middle ear effusions resolve spontaneously within 3 months. A persistent middle ear effusion in an adult requires exclusion of nasopharyngeal carcinoma, typically by nasal endoscopy.

PATHOPHYSIOLOGY AND CLINICAL PRESENTATION (1–10) Basic Mechanisms of Hearing and Its Impairment

Hearing impairment may result from an interference with the conduction of sound, its conversion to electrical impulses, or its transmission through the nervous system. Hearing involves an acoustic stage during which sound waves cause the tympanic membrane to vibrate. The tympanic membrane and the ossicles amplify the sound, and the oscillation of the footplate of the stapes in the oval window transmits the sound energy to the perilymph of the inner ear. The endolymph of the scala media (or cochlear duct) is wedged between the perilymph of the scala vestibuli and the scala tympani. Displacement of the basilar membrane stimulates the hair cells, converting sound waves to neural impulses, which are conveyed to the temporal lobes. On the molecular level, during the reception of sound, potassium ions flow through the upper surface of the cochlear hair cells; the ions then recycle by flowing down to the base and supporting cells and into the endolymph. Connexin , the “gap protein” that allows small molecules to pass from one cell to the next, facilitates this potassium flow. It is synthesized by the cells surrounding the sensory hair cells of the cochlea and by the fibrocytes of the cochlear duct. Interference with mechanical reception or amplification of sound, as occurs with disease of the auditory canal, tympanic membrane, or ossicles, creates conductive hearing loss . A conduc tive hearing loss is localizable to the external auditory canal or the middle ear in most cases. Degeneration or destruction of hair cells or the acoustic nerve produces sensorineural hearing loss , as do defects in the synthesis of connexin. Genetic studies have facilitated the uncovering of a molecular basis for hearing loss. Mutations in the gene that codes for connexin are associ ated with nonsyndromic hearing loss, both early in life and with aging (see later discussion). Congenital malformations of the inner ear, not necessarily hereditary, may also compromise hearing at the sensorineural level.

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