The complaint of dizziness is one of the most common reasons that older adults visit the doctor's office.1 The incidence of dizziness increases with age and accounts for 1.3% of all visits to internists in people 45 to 64 years old, 2.9% in people older than 65, and 3.8% in people older than 75. Although dizziness can be caused by many different medical conditions, it is estimated that as many as 45% of cases are a result of vestibular disorders.2 Aktas and colleagues3 have reported that in 31% of their subjects with hip fracture, vestibular disease was a comorbidity. In 80% of their patients with falls of unknown cause, Pothula and associates4 found symptoms of vestibular dysfunction. In a recent report of persons who reported dizziness who were over the age of 40 (n = 5,086), there was a 12-fold increase in their odds of falling within the last year.5 The vestibular insult or injury may be the same as in a younger individual, but the functional consequences may be very different because of the person's comorbid health status. Older adults with vestibular disorders, therefore, often present with very different problems from those of their younger counterparts. This chapter provides information about the normal changes in the vestibular, visual, and somatosensory systems with aging as well as the pathological changes that can occur in each system. Practical suggestions are made as to how older adults may be treated differently because of their age.
To appreciate the effect of aging on the mechanisms and potential for recovery in vestibular disease, one must understand the normal anatomy and physiology of the vestibular system (see Chapters 1–4). Several concepts are particularly important and will be emphasized here.
Semicircular Canal Function
The input from the receptors in the semicircular canals produces compensatory oculomotor responses (vestibuloocular reflex [VOR]) and compensatory postural responses (vestibulospinal reflex [VSR]). In the ideal situation, the eye movement produced by the head movement is equal (but opposite) to the head movement, and the VOR is said to have a gain (eye velocity ÷ head velocity) equal to 1. With aging, there is a decrease in the numbers of both hair cells and vestibular neurons.6–8 Functionally, VOR gain decreases, resulting in reduced visual compensation in response to head movement. These changes, however, appear to be frequency- and velocity-dependent.9,10 Baloh and coworkers11 found that older subjects had lower visual-VOR gain as velocity increased than younger subjects. If the visual-VOR gain decreases with age, especially at higher velocities,12 it would lead to greater retinal slip and therefore poorer visual acuity during head movement. The changes in vestibular function have been compared with a progressive bilateral vestibular deficit10,11,13...