Auditory dysfunction in aging and senile dementia of the Alzheimer's type

G. A. Gates, R. K. Karzon, P. Garcia, J. Peterein, M. Storandt, J. C. Morris and J. P. Miller
Virginia Merrill Bloedel Hearing Research Center, Department of Otolaryngology-Head and Neck Surgery, University of Washington, Seattle, USA.

OBJECTIVE: To determine the prevalence and type of auditory dysfunction in older volunteer subjects with mild probable Alzheimer's disease (pAD). METHODS: Pure-tone thresholds, word recognition in quiet, Synthetic Sentence Identification with Ipsilateral Competing Message or Contralateral Competing Message, distortion-product otoacoustic emissions, and auditory brain-stem responses were done in 82 elderly volunteer subjects whose cognitive, psychologic, and neurologic status had been determined through annual testing in a research center. Based on clinical criteria and the Clinical Dementia Rating (CDR) scale, 40 subjects had been judged to be nondemented (CDR score, 0), and 42 had a clinical diagnosis of pAD, with 22 in the questionable (CDR score, 0.5) and 20 in the mild (CDR score, 1) categories. RESULTS: The mean age-adjusted pure-tone average thresholds (0.5, 1.0, and 2.0 kHz) were poorer in the subjects with pAD by 5.1 dB in the right ears and 6.1 dB in the left ears; these differences were not statistically significant. Word recognition in quiet did not differ by CDR category. The age-adjusted scores on the Synthetic Sentence Identification with Ipsilateral Competing Message or Contralateral Competing Message were significantly reduced in the subjects with mild pAD. Distortion-product otoacoustic emission amplitudes and auditory brain-stem response thresholds and latencies paralleled the pure-tone threshold results and did not differ across the CDR groups. CONCLUSIONS: Central auditory dysfunction was evident in subjects with even mild cases of pAD, whereas peripheral auditory function was not different from that in age-matched control subjects. Additional research is needed to delineate the mechanisms of central auditory dysfunction and to establish the sensitivity and specificity of auditory testing in subjects with Alzheimer's disease. We recommend auditory assessment, including Synthetic Sentence Identification with Ipsilateral Competing Message or Contralateral Competing Message, for older patients in general and in particular for those in whom dementia is suspected.