Alzheimer disease with psychosis: excess cognitive impairment is restricted to the misidentification subtype

Psychotic symptoms occur in 30%-60% of individuals with Alzheimer disease (AD) with psychosis (AD+P). AD+P identifies a distinct AD phenotype, with increased severity of cognitive impairment and a more rapid cognitive decline. Using factor and cluster analysis, we previously proposed two subtypes of patients with AD+P, one characterized by misidentifications and hallucinations (Misidentification), the other by persecutory delusions (Paranoid). We hypothesized that these two groups differed in their patterns of cognitive impairment, compared with AD subjects without psychosis.

Subjects (N=119) with possible or probable AD were assessed with a comprehensive neuropsychological test battery at the time of initial presentation. Psychotic symptoms were ascertained with the CERAD Behavioral Rating Scale. Cognitive test scores were compared among groups by use of general linear-regression models, with age, education, and duration of illness entered as covariates. All results were corrected for multiple comparisons.

The Misidentification group was significantly more impaired than the Non-Psychotic group on tests of verbal fluency and visuospatial function. The Paranoid group did not differ from the Non-Psychotic group on any test.

These results support the identification of the Misidentification and Paranoid groups as distinct subgroups of AD+P. The ability to detect meaningful biologic associations of AD+P in future studies would be enhanced by separate analysis of the Misidentification and Paranoid phenotypes.