Associated illness severity in schizophrenia and diabetes mellitus: A systematic review

•Schizophrenia may share inflammatory disease links with Diabetes Mellitus.•Research has little focussed on whether the severity of illnesses may be shared.•Our comprehensive systematic review featured 11 observational studies.•Negative symptoms and cognitive function may be associated with diabetes severity.•Future work may seek to focus on first-episode psychosis patients.

ObjectiveWe aimed to elucidate whether schizophrenia and type II diabetes mellitus may present with associated illness severity, in light of accumulating evidence to suggest both conditions have important shared inflammatory components with many shared inflammatory genetic factors.MethodsWe conducted a systematic review employing PRISMA criteria, searching EMBASE, Ovid MEDLINE, PsychInfo, Web of Science and Google Scholar to February 1st, 2017, for clinical studies assessing schizophrenia severity alongside dysglycaemia. A narrative synthesis was employed to discuss and compare findings between studies.ResultsEleven observational studies were included in the analysis. Ten presented evidence in support of an association between schizophrenia severity and dysglycaemia. This association appeared particularly strong regarding negative symptomatology and impaired cognitive function, between which there may be some overlap. Studies examining positive symptomatology returned mixed results.ConclusionWhilst study design varied amongst the included studies, the results suggest that further work examining the effect of hyperglycaemia on schizophrenia severity may be relevant, particularly longitudinal studies assessing negative symptomatology and cognitive function. To the authors' knowledge, this is the first systematic review conducted to address this question.