Performance on the cognitive abilities screening instrument at different stages of Alzheimer's disease

The Cognitive Abilities Screening Instrument (CASI) contains nine cognitive domains. Its total score has been used to screen for dementia in epidemiological studies conducted in the US, Japan and Taiwan, but its usefulness in distinguishing different levels of dementia has not been examined. This study was conducted to compare CASI scores of patients with Alzheimer's disease (AD) with different levels of severity of dementia. The CASI was administered to 475 AD patients with mild, moderate or severe dementia according to the Clinical Dementia Rating Scale. The patients' scores were compared to the scores of 475 age-, education- and gender-matched control subjects. More specifically, each patient's score, X, was transformed to a z score with reference to the mean and SD of the scores of the control group, where z = (X - mean)/SD. Then, the mean of the z scores and the percentage of patients with z scores of <-2.0 were compared among the three patient groups. For the CASI total score and all of its nine domain scores, the mean z score decreased (except that for short-term memory) and a higher percentage of patients scored below the normal range with increasing severity of dementia. This study validates the usefulness of the CASI for assessing the severity of dementia. The domain scores differed in their relative usefulness for detecting dementia and for distinguishing in different levels of dementia.