Association of cognitive performance with clinical staging in schizophrenia spectrum disorders: a prospective 6-year follow-up study

Background: Clinical staging has been developed to capture the large heterogeneity in schizophrenia spectrum disorders. Including cognitive performance in the staging model may improve its clinical validity. Moreover, cognitive functioning could predict transition across stages. However, current evidence of the association between cognition and clinical staging is inconsistent. Therefore, we aim to assess whether cognitive parameters are associated with clinical stages in a large sample of patients with schizophrenia spectrum disorders and to identify cognitive markers at baseline that are associated with stage-transition at three and six-year follow-up. Methods: We applied the staging model of Fusar-Poli et al. (2017) in 927 patients with non-affective psychotic disorders, assessed at baseline, and after three and six-year follow-up. Cognitive performance was assessed with a standard test battery. Generalized linear mixed models were used to analyze associations of cognitive performance with staging and stage-transition at follow-up. Results: Findings showed that higher stages of illness were significantly associated with lower processing speed (F = 3.688, p = 0.025) and deficits in working memory (F = 6.365, p = 0.002) across assessments. No associations between cognitive parameters at baseline and stage-transition at three-and six-year follow-up were found. Conclusion: We conclude that processing speed and working memory were modestly associated with higher stages of illness in schizophrenia spectrum disorders, thereby slightly improving its clinical validity. However, associations were small and we found no evidence for predictive validity.