Shared and divergent neurocognitive impairments in adult patients with schizophrenia and bipolar disorder: Whither the evidence?

Abstract

Recent data from genetic and brain imaging studies have urged rethinking of bipolar disorder (BD) and schizophrenia (SCZ) as lying along a continuum of major endogenous psychoses rather than dichotomous disorders. We systematically reviewed extant studies (from January 2000 to July 2015) that directly compared neurocognitive impairments in adults with SCZ and BD. Within 36 included studies, comparable neurocognitive impairments were found in SCZ and BD involving executive functioning, working memory, verbal fluency and motor speed. The extent and severity of neurocognitive impairments in patients with schizoaffective disorder, and BD with psychotic features occupy positions intermediate between SCZ and BD without psychotic features, suggesting spectrum of neurocognitive impairments across psychotic spectrum conditions. Neurocognitive impairments correlated with socio-demographic (lower education), clinical (more hospitalizations, longer duration of illness, negative psychotic symptoms and non-remission status), treatment (antipsychotics, anti-cholinergics) variables and lower psychosocial functioning. The convergent neurocognitive findings in both conditions support a continuum concept of psychotic disorders and further research is needed to clarify common and dissimilar progression of specific neurocognitive impairments longitudinally.

Keywords: Bipolar disorder; Neurocognitive impairments; Schizophrenia.