Central auditory dysfunction as a harbinger of Alzheimer dementia.

OBJECTIVE To confirm that central auditory dysfunction (CAD) may be a precursor to the onset of Alzheimer dementia (AD). DESIGN Cohort study. SETTING Research study center. PARTICIPANTS Two hundred seventy-four volunteers from a dementia surveillance cohort were followed up for as long as 4 years after undergoing complete audiometric assessment. Twenty-one received a consensus diagnosis of AD after a hearing test. INTERVENTION The following 3 central auditory tests were performed: the Dichotic Sentence Identification, the Dichotic Digits, and the Synthetic Sentence Identification With Ipsilateral Competing Message. MAIN OUTCOME MEASURES A new diagnosis of AD using the National Institute of Neurological and Communicative Diseases and Stroke-Alzheimer Disease and Related Disorders Association criteria at a consensus conference. RESULTS The mean scores on each CAD test were significantly poorer in the incident dementia group. Cox proportional hazards models with age as the time scale were used to estimate the hazard ratio for incident dementia based on CAD test results. After adjusting for educational level, the hazard ratio for incident dementia in people with severe CAD based on a Dichotic Sentence Identification in free report mode of less than 50% was 9.9 (95% confidence interval, 3.6-26.7). CONCLUSIONS Central auditory dysfunction is a precursor to AD. We recommend evaluation with CAD tests in older adults who report hearing difficulty. Those with severe CAD should receive a modified rehabilitation program and be considered for referral for neurologic evaluation.