Aging and the Auditory and Vestibular System



Aging and the Auditory and Vestibular System


Joe Walter Kutz Jr.

Brandon Isaacson

Peter S. Roland



The geriatric population is the fastest growing segment of the population of all industrialized nations, including the United States. As life expectancy increases and health care costs rise, the medical profession will be challenged to provide cost-effective quality care. A recent report by the Institute of Medicine (IOM) predicted the percentage of Americans older than 65 will increase by 20% and double in number from 35 million to 71 million by the year 2030 (1). Since age-related hearing loss is the fourth most common reason patients over 65 years old seek medical care and vestibular dysfunction is common in the older population, there is going to be a substantial increase in the number of outpatient visits for otologic conditions. A recent study by Lin and Bhattacharyya (2) predicted a 30% increase in annual visits to otolaryngologists for otologic diagnoses by 2020. Understanding and treating disorders of the aging auditory and vestibular systems will be more essential than ever for the otolaryngologist.

Greater than 40% of patients older than 65 years have a hearing loss that significantly impairs communication and leads to a decrease in quality of life (3). Loss of hearing negatively affects social interaction, leading to progressive isolation and withdrawal. In addition, high-frequency warning sounds such as alarms and signals may not be heard, resulting in potential harm. Although hearing loss in the geriatric population is often due to presbycusis, other causes should be sought.

Dizziness is the most common presenting complaint in patients 75 years or older and typically affects women more than men (4). Balance disturbances contribute to functional decline in the elderly. Postural stability and gait involves the complex integration of the visual, proprioceptive, somatosensory, and vestibular signals. Pathology in any of these systems can cause dizziness and, more importantly, increase the incidence of falls. It is estimated that approximately 40% of older adults living in the community have at least one fall per year. In a study by the Centers for Disease Control (CDC), 62% of injuries presenting to the emergency department in patients older than 65 years were a direct result of a fall (5). A hip fracture is a common serious injury resulting from a fall and often leads to serious long-term consequences. Only 50% of elderly patients can return home or return to normal activity after a hip fracture (6,7).

The differential diagnosis for dizziness is extensive, sometimes making the evaluation laborious and difficult. However, 90% of the causes of dizziness can be placed in one of seven categories (Table 162.1). One recent study evaluating the cause of dizziness in 677 elderly patients identified benign paroxysmal positional vertigo (BPPV) in 42%, idiopathic vestibulopathy in 20%, migraine-associated dizziness in 13%, Meniere disease in 12%, and an acute vestibular attack in 6%, and 7% contributed to other causes (8).


AGE-RELATED CHANGES IN THE AUDITORY SYSTEM


Auditory Dysfunction

All of the usual cases of hearing loss can affect the elderly (Table 162.2). These disorders are addressed elsewhere in this textbook. With the exception of conductive loss associated with aging as described by Schuknecht, conductive hearing loss in the elderly population has the same differential diagnosis as in younger individuals.

Anatomic changes that affect hearing and balance occur because of physiologic aging. One such example involves the production of cerumen. Cerumen consists of desquamated epithelium mixed with the sebum produced from sebaceous glands and the watery secretions of modified apocrine sweat glands. Modified apocrine sweat glands atrophy with age. Without the watery component, cerumen becomes drier, harder, and less likely to be moved out the external auditory canal (EAC) by the canal’s normal transport and cleansing mechanism. The tragi hairs found in adult males become coarser, larger, and more prominent with age. Their
presence can prevent the natural dislodgement of cerumen from the EAC, contributing to the increased incidence of cerumen impaction in the elderly male.








TABLE 162.1 ETIOLOGY OF DIZZINESS

















Peripheral vestibular disorders


Cardiovascular disorders


Multisensory dizziness


Brainstem cerebrovascular disease


Neurologic disorders


Psychiatric disease


Hyperventilation syndrome









TABLE 162.2 CAUSES OF BILATERALLY SYMMETRIC SENSORINEURAL HEARING LOSSa

















































Ménière disease


Episodic attacks of fluctuant SNHL, vertigo, tinnitus, aural fullness or pressure; bilateral in 20%-30% of cases


History of typical attacks with symptom-free intervals; hearing loss involves low tones initially and later all frequencies, rule out neurosyphilis


Medical


Diuretics and low-salt diet


Surgical


Decompression or shunt of endolymphatic sac; section of vestibular nerve.


Penicillin and oral steroids


Luetic hearing loss (late-acquired syphilis)


Often bilateral SNHL with no characteristic audiometric pattern; speech discrimination score often worse than would be predicted on basis of pure-tone thresholds; often associated with vestibular symptoms; may mimic Ménière disease


Positive FTA-ABS test, with or without clinical history of syphilis


Paget disease


Slowly progressive SNHL and CHL; SNHL worse in high frequencies; maximum CHL of 20-30 dB at 500 Hz


Skeletal deformities of skull and long bones of extremities, elevated serum alkaline phosphatase and urinary hydroxyproline


Calcitonin


Hypothyroidism


Slowly progressive SNHL affecting all frequencies daily


Usual clinical stigmata of hypothyroidism; decreased serum T4


Desiccated thyroid or Synthroid mixture of T4 and T3


Ototoxic drugs


Hearing loss with or without vestibular dysfunction following treatment with known ototoxic drug


History


None


Hereditary progressive SNHL


Progressive SNHL beginning at earlier age than expected for presbycusis; possible positive family history


Family history


None


Noise-induced hearing loss


History of prolonged exposure to loud continuous noise or brief exposure to loud impulse noise


History; characteristic audiogram with maximum hearing loss at 4,000 Hz; may not be distinguishable from presbycusis


None; use of ear protectors may prevent further loss from noise exposure


Head trauma


Severe head injury often resulting in loss of consciousness and bilateral temporal bone fractures


History


None


Cochlear otosclerosis and far-advanced clinical otosclerosis


Far-advanced clinical otosclerosis (stapedial fixation) and cochlear otosclerosis; SNHL may appear on audiogram as severe to profound SNHL; patient will have good speech modulation (unlike in profound SNHL) and will be wearing or will have worn a bone conduction hearing aid; possibly a family history of otosclerosis


History is suggestive but surgical exploration of stapes footplate is diagnostic and therapeutic; poststapedectomy patient may be able to wear ear-level hearing aid with good results


Stapedectomy, sodium fluoride


aThe hearing loss from any of these diseases may be improved with hearing aids unless it is of such a degree that hearing aids will be inadequate or unsatisfactory. Individuals with bilateral profound SNHL may be candidates for cochlear implant and should be evaluated by an otologist to determine their suitability for such a device.
SNHL, sensorineural hearing loss; FTA-ABS test, fluorescent treponemal antibody test, CHL, conductive hearing loss; Hz, hertz (cycles per second); dB, decibel (arbitrary unit of sound intensity).



Presbycusis

The auditory system’s durability is determined by genetic resistance and the cumulative imposed physical stress. Genetically mediated hearing loss can be difficult to distinguish from presbycusis. The ability to differentiate hearing loss caused by defective genetic material is increasing
as the types and tests of chromosomal abnormalities are identified. In any given individual, though, it is difficult to determine what component of the hearing loss is due to inherent genetic determination and what component is a consequence of stresses imposed, such as acoustic trauma, viral infections, otologic disease, vascular diseases, and ototoxic medications. Multiple variables have been evaluated that contribute to hearing loss associated with aging (Table 162.3).








TABLE 162.3 FACTORS CONTRIBUTING TO AGE-RELATED HEARING LOSS













Microvascular disease resulting in diminished profusion and hypoxia of labyrinthine hair cells and neurons


Effects of diet; in animals, free radical formation increases hearing loss


Noise exposure


Drug effects


Cigarette smoking


A well-documented phenomenon in elderly subjects is the disproportionate deterioration of speech discrimination for any given pure-tone threshold shift (Fig. 162.1). Tests of central auditory processing include time-compressed speech (word rate per min) and overlapping or interruption of words. These tests suggest that older patients have poorer speech discrimination than younger patients because of changes in central auditory processing. Decreased cell counts in the temporal lobes, increased time required for information processing, and possibly increased transmission time in the central auditory pathways have all been identified as potential factors in central auditory processing disorders in the elderly (9). Elderly patients demonstrate mildly prolonged latencies and reduced wave I amplitudes on the auditory brainstem response (ABR) (10,11).






Figure 162.1 Average speech discrimination score as a function of age with the average pure-tone threshold held constant. PTA, pure-tone average. From Jerger J. Audiological findings in aging. Adv Otorhinolaryngol 1973;20:115-124.








TABLE 162.4 CLINICAL MANIFESTATIONS OF PATHOLOGIC CHANGES WITHIN THE COCHLEA











Cochlear hair cell loss progresses the high-frequency hearing loss with speech discrimination preserved in the initial phases.


Neuronal loss: a nonprecipitous, generalized loss of pure-tone thresholds with speech discrimination impaired out of proportion to the threshold shift.


Atrophy of the stria: flat hearing loss with good preservation of speech discrimination.


Mechanical (cochlear conductive): gradually sloping high frequency hearing loss with speech discrimination impaired proportionate to the pure tone threshold shift.


Schuknecht identified four categories of presbycusis based on clinical and histopathologic changes within the cochlea (Table 162.4):



  • Sensory: epithelial atrophy with loss of sensory cells and the supporting cells of the organ of Corti. Progressive hair cell reduction begins at about age 40. A precipitous decline in pure tone thresholds is seen in the high frequencies.


  • Neural: a reduction in the number of functioning cochlear neurons. Of the 35,500 cochlea neurons at birth, Schuknecht has estimated that 2,100 neurons are lost each decade. When reduction has reached 50% or more of the normal neuronal population, hearing loss develops. This spiral ganglion cell loss also results in a progressive decline in speech discrimination.


  • Strial: atrophy of the stria vascularis. A loss of 30% or more of strial tissue can result in hearing loss characterized by flat hearing loss with relative preservation of speech discrimination.


  • Conductive: alterations of the basilar membrane produce stiffening. The precise nature of these changes is partially hypothesized on the basis of conductive loss that remains otherwise unexplained.


Although this classification is interesting, each of the four changes may be found to various degrees in any one individual subject; consequently, the audiograms of elderly individuals rarely conform to these classic patterns.


Auditory Rehabilitation

Increased awareness of the prevalence of presbycusis is important, as those with hearing loss tend to be more socially withdrawn and isolated. Patients tend to become frustrated, as do those trying to communicate with them. The main treatment for presbycusis is amplification. Cochlear implantation is an option for some, depending on the severity of the hearing loss. Assistive listening devices (such as FM systems, speaker phones, etc.) are also beneficial. Patient should be instructed to increase the signal-to-noise ratio of their surroundings by reducing the ambient background noise in a room and having someone look directly at them.

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May 24, 2016 | Posted by in OTOLARYNGOLOGY | Comments Off on Aging and the Auditory and Vestibular System
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