Progression of cognitive impairment in Alzheimer's disease.

Change in cognitive function was assessed over 12 months in 110 patients over the age of 65 satisfying National Institute of Neurological and Communicative Disorders and Stroke and the Alzheimer's Disease and Related Disorders Association (NINCDS/ADRDA) criteria for "probable" Alzheimer's Disease. A highly significant deterioration in cognitive function was observed. Decline in cognitive scores was relatively normally distributed. Patients who died during the follow-up had more apraxia at entry to the study than survivors. A greater rate of decline was seen in patients whose parents suffered from dementia (but not in those where a sibling or other relative was affected), in subjects who had moderate dementia, and those who had been ill for less than 24 months. Age, age of onset, and the presence or absence of aphasia or apraxia had no influence on rate of progression. A cluster analysis revealed three patterns of decline.