Cumulative risks of developing extrapyramidal signs, psychosis, or myoclonus in the course of Alzheimer's disease.

Cumulative risks of developing extrapyramidal signs, psychosis, and myoclonus in the course of Alzheimer's disease (AD) were estimated in 72 patients with probable AD by the Kaplan-Meier survival method. The cumulative risk functions were found to increase at different rates for different signs as AD progressed. Comparisons of the cumulative risk functions revealed that in the early stages of AD, extrapyramidal signs and psychosis were more likely to develop than myoclonus. As AD progressed, the risk of developing myoclonus became as great as that of developing the other two signs. This study suggests that extrapyramidal signs, psychosis, and myoclonus represent developmental features that mark the progression of AD, rather than indicators of disease subtypes. The estimated cumulative risk functions set a reasonable expectation for the timing and likelihood of the emergence of the clinical signs. This, in turn, might aid in disease prognosis because the biological bases of these signs have been established and they have been shown to be predictive of other markers of disease course.