Assessing the prevalence of cognitive impairment among Australians with schizophrenia: A systematic review

Cognitive difficulties are a core feature of psychotic disorders such as schizophrenia; however, the prevalence of cognitive impairment among Australians with schizophrenia is unclear. This review aimed to estimate the prevalence of cognitive impairment associated with schizophrenia in Australia and to describe methodological approaches to assessing cognition and defining cognitive impairment in the Australian schizophrenia research literature.

Systematic searches were conducted across MEDLINE Complete, APA PsycINFO, Embase and Scopus to identify studies reporting cognitive assessment outcomes among Australians diagnosed with schizophrenia or schizoaffective disorder. A particular focus was given to studies of naturalistic cohorts (those studied in real-world environments without manipulation or experimental intervention); however, clinical trial cohorts were also included. Reporting followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 statement and Synthesis Without Meta-analysis guidelines.

Findings were synthesised from 198 studies comprising approximately 23,755 individuals. There was substantial heterogeneity in cognitive assessment approaches and definitions of cognitive impairment. Over 100 different cognitive tests and test batteries were used across the included studies. Only 11 studies described naturalistic cohorts, with reported prevalence estimates of cognitive impairment of between 14.5% and 90%. Given insufficient quantitative data and substantial methodological differences across studies, meta-analysis was not conducted.

Although a pooled prevalence estimate could not be calculated, cognitive impairment likely poses a substantial burden to Australians with schizophrenia. Reducing this burden requires a multifaceted approach, including improved access to cognitive assessments as part of routine clinical care, and improved availability of evidence-based cognition-focused treatment options.