Comparison between clinical diagnosis and CSF biomarkers of Alzheimer disease in elderly patients with late onset psychosis: Helsinki Old Age Psychosis Study (HOPS).

Objectives: To determine the proportion of elderly people with a first psychotic episode actually suffering from dementia, especially Alzheimer disease (AD), by using cerebrospinal fluid (CSF) biomarkers.

Design: Prospective case-control study.

Setting And Participants: Sixty-six patients age 65 years and older with recent psychotic symptoms and 12 comparison subjects with chronic schizophrenia over 10 years that were referred to acute old age psychiatry, in-ward treatment.

Measurements: Concentration levels of CSF Aβ42, tau and p-tau-181 measured by ELISA compared to clinical diagnosis made by a multiprofessional team of one neurologist and several psychiatrists.

Results: The CSF specimen was obtained from 51 (65.4%) of the patients. In five subjects out of 13 with a clinical diagnosis of AD, all the CSF biomarkers (Aβ42, tau and p-tau) were normal. Only one patient out of 25 with a psychiatric diagnosis and none out of the comparison group with schizophrenia showed a CSF profile typical of AD. Three patients with an AD diagnosis, four patients with a psychiatric diagnosis and one patient with schizophrenia had a low Aβ42 concentration with normal levels of tau or p-tau. The patients with AD had lower CSF Aβ42 levels than other patients.

Conclusions: The CSF biomarkers are important and useful as part of the diagnostic procedure for detecting AD and other dementia in elderly patients displaying psychotic symptoms. The accuracy of AD diagnosis encounters problems due to atypical behavioural symptoms in psychiatric settings and thus the differential diagnostics can be improved by using CSF biomarkers of AD more frequently.