Motor dysfunction in mild cognitive impairment and the risk of incident Alzheimer disease

Background: Little is known about motor function in mild cognitive impairment (MCI) and its relation to the risk of Alzheimer disease (AD). Objective: To examine motor function in persons with MCI and its relation to risk of AD. Design: Longitudinal cohort study. Setting: More than 40 Catholic religious orders across the United States. Participants: We studied 816 older Catholic clergy members from the Religious Orders Study. At the baseline evaluation, they were classified as having no cognitive impairment (n = 558), MCI (n = 198), or dementia (n = 60). Main Outcome Measures: Motor function was assessed at baseline using performance-based measures of upper and lower extremity function and a modified version of the motor section of the Unified Parkinson's Disease Rating Scale, from which previously established measures of parkinsonian signs were derived. Clinical evaluations for dementia and AD were repeated annually for up to 10 years. All analyses controlled for age, sex, educational level, and possession of at least 1 apolipoprotein E epsilon 4 allele. Results: At baseline, individuals with MCI had impaired motor function relative to those without cognitive impairment and superior motor function vs those with dementia. Among those with MCI, baseline levels of lower extremity motor performance, parkinsonian gait, and bradykinesia were inversely related to risk of AD, even after controlling for clinical stroke. Thus, a person with impaired lower limb performance or parkinsonian gait (10th percentile) was 2 to 3 times more likely to develop AD than a person with good lower limb function (90th percentile). Conclusions: Persons with MCI also have impaired motor function, and the degree of impairment in lower extremity function is related to the risk of AD.