Multicenter study of predictors of disease course in Alzheimer disease (the 'Predictors Study'). II. Neurological, psychiatric, and demographic influences on baseline measures of disease severity

The 'Predictors Study' is a prospective cohort study of the natural history of Alzheimer disease (AD), the aim of which is to identify milestones in disease progression and to develop a model to predict disease course in individual patients. The empirical background to this study is based on previous reports that the presence of extrapyramidal signs (EPS), myoclonus, and psychosis in AD may signify greater disease severity at any given stage and a more rapid course of the disease over time. The present analyses were conducted to determine whether these independent 'predictor' variables were associated with greater disease severity at baseline within a new cohort of 224 mild AD patients recruited from three different medical centers (in New York, Baltimore, and Boston). Measures of disease severity were provided by the modified Mini-Mental State Examination (mMMSE) and the Blessed Dementia Rating Scale (BDRS), which measures functional capacity. Independent variables were EPS, delusions, and slowing of the posterior dominant EEG rhythm. The frequency of myoclonus and hallucinations was too low to permit adequate statistical assessment of their effects at this time. EPS and EEG slowing were associated with low mMMSE scores, whereas delusions were primarily associated with impaired functional capacity. These effects were independent of the influence of age and disease duration. These results indicate that the effects of these independent variables can be detected at mild stages of AD and that these effects can be generalized across different geographical regions.