Hearing impairment and cognitive decline in senile dementia of the Alzheimer's type.

Hearing impairment has been hypothesized as contributing to symptoms of dementia. Data from a longitudinal study were analyzed to determine if auditory status predicted cognitive functional decline in senile dementia of the Alzheimer's type (SDAT). As part of a larger study, 156 consecutive SDAT outpatients had received a comprehensive medical evaluation including baseline screening for hearing impairment with the finger friction test and serial assessment of cognitive function with the Mini-Mental State examination. Age and cognitive function at entry to the study were greater among individuals with impaired hearing (N = 36) than with normal hearing (N = 120). The demographic profiles of the impaired and normal hearing groups were otherwise similar, as was the prevalence of depression. Intervening mortality rates were nearly identical. Decline in cognitive function one year later, however, was nearly twice as great in the impaired hearing group, a statistically significant difference (P less than .05, by one-tailed t test) even when controlled for age and initial cognitive function. These results, which need to be verified with sophisticated audiometric techniques, suggest that hearing impairment may be a prognostic indicator for subsequent cognitive dysfunction in SDAT. They are consistent with the hypothesized relationship between hearing impairment and dementia in SDAT as well as alternative hypotheses discussed in the text.