Cognitive performance, symptom severity, and survival among patients with schizophrenia spectrum disorder: A prospective 15-year study

Abstract

Patients with schizophrenia have an average lifespan approximately 20years shorter than the normal population. This study explored if there were any specific common characteristics among patients with schizophrenia spectrum disorder who died prematurely, compared to those who survived or died at a more normative age. The data were obtained from an ongoing twenty-year longitudinal study wherein 67 patients out of 501 participants had died at an average age of 60.5years. Differences in baseline assessments of symptoms and cognitive ability were compared across patients who died during the time of the study and survivors. Symptom remission was assessed according to the Andreasen remission criteria as presented in 2005. Cognitive performance was assessed with a battery of instruments measuring vigilance, working memory, learning, short-term memory, and executive function. Two patients committed suicide and together they lowered the average lifespan of the study sample by only 0.27years. The baseline assessments showed no difference in symptoms or remission status between patients who died and those who survived. This finding was in contrast to the cognitive baseline assessments where it was found that those who had died had performed more poorly in multiple domains, especially executive functioning, cognitive flexibility, learning and short-term memory. Survival analysis with Cox models showed that verbal memory and executive functioning were the most substantial independent predictors. Our study shows that although suicide was not a common cause of death, the average age of death is still young for this patient group and cannot be explained by differences in symptom severity. Our findings indicate that cognitive abilities might be of special interest for affective longevity in patients with schizophrenia, either as a marker of special risk or as a target for direct intervention.