The mediating role of depression in pathways linking positive and negative symptoms in schizophrenia. A longitudinal analysis using latent variable structural equation modelling

Background: The interaction between positive, negative and depressive symptoms experienced by people with schizophrenia is complex. We used longitudinal data to test the hypothesis that depressive symptoms mediate the links between positive and negative symptoms. Methods: We analyzed data from the European Schizophrenia Cohort, randomly sampled from outpatient services in France, Germany and the UK (N = 1208). Initial measures were repeated after 6 and 12 months. Depressive symptoms were identified using the Calgary Depression Scale for Schizophrenia (CDSS), while positive and negative symptoms were assessed with the Positive and Negative Syndrome Scale (PANSS). Latent variable structural equation modelling was used to investigate the mediating role of depression assessed at 6 months in relation to the longitudinal association between positive symptoms at baseline and negative symptoms at 12 months. Results: We found longitudinal associations between positive symptoms at baseline and negative symptoms at 12 months, as well as between both of these and CDSS levels at 6 months. However depression did not mediate the longitudinal association between PANSS scores; all the effect was direct. Conclusions: Our findings are incompatible with a mediating function for depression on the pathway from positive to negative symptoms, at least on this timescale. The role of depression in schizophrenic disorders remains a challenge for categorical and hierarchical diagnostic systems alike. Future research should analyze specific domains of both depressive and negative symptoms (e.g. motivational and hedonic impairments). The clinical management of negative symptoms using antidepressant treatments may need to be reconsidered.