Phenotypic cognitive impairment in late-onset delusional disorder.

BACKGROUND: Previous use of heterogeneous diagnostic criteria and insensitive cognitive measures has impeded clarification of the extent and type of cognitive impairment specific to late-onset delusional disorder. We examined whether clinical presentations of late-onset delusional disorder are associated with prodromal or established dementia, and whether it might be a discrete clinical syndrome characterized by its own profile of cognitive impairment.

METHOD: Nineteen patients with late-onset delusional disorder from a hospital psychiatric service and 20 patients with dementia of the Alzheimer's type (AD) from an outpatient memory clinic were recruited in a consecutive case series. All patients underwent comprehensive neuropsychological assessment that included general intellectual function, executive function, new learning and delayed memory, language, processing speed, and visuo-perceptual skills.

RESULTS: Late-onset delusional disorder patients showed moderate impairment to conceptual reasoning, visual object recognition, processing speed, and confrontation naming. Severe impairment appeared in visuo-perceptual planning and organization, and divided attention. Compared with the Alzheimer's disease (AD) group, the late-onset delusional disorder group demonstrated significantly poorer visuo-perceptual skills but a significantly better capacity to consolidate information into delayed memory.

CONCLUSIONS: A high rate of marked cognitive impairment occurs in late-onset delusional disorder. There was evidence of a conceptual reasoning deficit, plus the presence of a visuo-perceptual impairment affecting object recognition. This impairment profile can explain the genesis and maintenance of the observed delusions. Understanding late-onset delusional disorder as other than a purely psychiatric phenomenon or a precursor to AD will lead to better assessment and management approaches.