A meta-analysis comparing cognitive function across the mood/psychosis diagnostic spectrum

Abstract

Background The nature and degree of cognitive impairments in schizoaffective disorder is not well established. The aim of this meta-analysis was to characterise cognitive functioning in schizoaffective disorder and compare it with cognition in schizophrenia and bipolar disorder. Schizoaffective disorder was considered both as a single category and as its two diagnostic subtypes, bipolar and depressive disorder. Methods Following a thorough literature search (468 records identified), we included 31 studies with a total of 1685 participants with schizoaffective disorder, 3357 with schizophrenia and 1095 with bipolar disorder. Meta-analyses were conducted for seven cognitive variables comparing performance between participants with schizoaffective disorder and schizophrenia, and between schizoaffective disorder and bipolar disorder. Results Participants with schizoaffective disorder performed worse than those with bipolar disorder (g = −0.30) and better than those with schizophrenia (g = 0.17). Meta-analyses of the subtypes of schizoaffective disorder showed cognitive impairments in participants with the depressive subtype are closer in severity to those seen in participants with schizophrenia (g = 0.08), whereas those with the bipolar subtype were more impaired than those with bipolar disorder (g = −0.23) and less impaired than those with schizophrenia (g = 0.29). Participants with the depressive subtype had worse performance than those with the bipolar subtype but this was not significant (g = 0.25, p = 0.05). Conclusion Cognitive impairments increase in severity from bipolar disorder to schizoaffective disorder to schizophrenia. Differences between the subtypes of schizoaffective disorder suggest combining the subtypes of schizoaffective disorder may obscure a study's results and hamper efforts to understand the relationship between this disorder and schizophrenia or bipolar disorder.

A neuropsychological study on Leonhard’s nosological system

“…Another remarkable finding of our study was the lack of significant differences among some basic cognitive domains, such as attention, and regarding higher-order cognitive functions, such as executive functions and social cognition. However, the results on attention are in agreement with the lack of differences reported in two meta-analyses examining cognitive function across psychotic disorders [11,12].…”

“…Comparisons among the psychosis subtypes have been mostly based upon several versions of the DSM (Diagnostic and Statistical Manual of Mental Disorders) classification [10]. Small to moderate effect sizes of significant differences on neuropsychological examinations have been consistently reported among schizophrenia, schizoaffective and bipolar disorders, with schizoaffective patients showing less cognitive impairment than those with schizophrenia but greater cognitive impairment than bipolar patients [11,12]. These differences seem to be more dependent on premorbid cognitive abilities or cognitive reserve [13,14] and patterns of neurodevelopment processes [15].…”