Cognitive trajectories and dementia risk in patients with schizophrenia spectrum versus affective disorders.

Background: Schizophrenia spectrum disorders confer an increased and earlier dementia diagnosis risk, but the relative timing and course of cognitive decline compared to individuals with affective disorders is unclear.

Methods: This retrospective study used de-identified electronic patient records to compare cognitive trajectories from the first recorded MMSE, representing the earliest cognitive concerns in relation to a possible dementia syndrome, and subsequent dementia risk between patients with a schizophrenia spectrum and primary affective disorder diagnosis. Patients had at least two MMSE scores recorded at least 6 months apart. We examined annual MMSE change from the first recorded MMSE, dementia risk, dementia subtypes, and rates of dementia assessment and treatment.

Results: Compared to affective disorders (n = 2,264; 71.1 years), schizophrenia spectrum disorders (n = 1,217; 65.0 years) showed earlier initial MMSE scores (by 6.1 years, 95% CI = 5.2-7.0), earlier dementia diagnoses (by 2.3 years, 95% CI = 0.9-3.7) but lower dementia risk (adjusted HR = 0.81; 95% CI = 0.69-0.95). Cognitive decline rates and dementia subtype diagnoses did not differ between affective and schizophrenia spectrum disorders, but it took longer for schizophrenia spectrum disorder patients to receive a dementia diagnosis (5.6 vs. 4.4 years). Anti-dementia medication was less likely to be prescribed in patients with schizophrenia versus depression.

Conclusions: Cognitive concerns in older individuals with schizophrenia spectrum disorders arise from around 63 years and are associated with earlier dementia risk versus older individuals with affective disorders. Findings emphasize the importance of targeted dementia prevention and treatment strategies in these individuals and the need to reduce the existing inequity of access to dementia services.