Longitudinal analysis of clock drawing in Alzheimer's disease patients.

Longitudinal changes in the role of conceptual, spatial, and graphic processes in the drawing deficits of patients with Alzheimer's disease (AD) were assessed over a 2-year period. Both the drawing-to-command and copy conditions of the Clock Drawing Test were administered to 33 AD patients as part of three consecutive annual examinations. The drawings from each administration were evaluated for overall accuracy and the types of errors manifested. Although the patients showed a gradual decline in overall accuracy on both command and copy conditions over the three test sessions, they performed more poorly and evidenced a steeper decline on the command condition. Conceptual errors in the command condition were noted in the early stages of AD and increased over the three administrations. Stimulus-bound errors were usually associated with conceptual errors in the same or in a contiguous year. When the patients' performances on the first test session were correlated with their yearly scores on Mattis' Dementia Rating Scale, the presence of conceptual errors was associated with a steep decline on this measure of mental status. These results suggest that drawing deficiencies in AD often reflect impairments in conceptualization and semantic knowledge and that such losses may prove useful in predicting the disease's rate of progression.