Psychotic symptoms in Alzheimer disease: evidence for subtypes.

OBJECTIVE: Psychotic symptoms in Alzheimer disease (AD) identify a phenotype with distinct neurobiology and genetic architecture. The authors investigated whether AD with psychosis is homogeneous or is a composite of subtypes. METHODS: Authors performed factor and cluster analyses of the psychotic-symptom items of the CERAD Behavioral Rating Scale in 188 probable and possible AD subjects who have displayed at least one psychotic symptom. RESULTS: Exploratory factor analysis resulted in a one-factor solution that comprised misidentification delusions, auditory and visual hallucinations, and the misidentification of people. Persecutory delusions were also frequently present and were independent of the misidentification/hallucination factor. Cluster analysis yielded similar results. CONCLUSION: Misidentification/hallucinations and persecutory delusions may identify two subtypes of psychosis in AD. Longitudinal study is needed to determine whether these proposed subtypes remain stable and independent over time or merge into a single group over the course of illness.