The course of the schizophrenia and its impact on cognition: a review of literature.

There has been increasing interest about cognition in schizophrenia during recent years. The greater focus of the investigators has been focused greater interest on the relation of cognitive deterioration with positive and negative symptoms, and functionality. However very few studies, if any, have specifically focused on the course of cognition in schizophrenic patients throughout the years. Those who have attempted to answer this question have done so by comparing cross-sectional studies of patients at different stages of their disease. Only a minority have used a longitudinal methodology in their studies. This article reviews a total of 31 cross-sectional and 43 longitudinal studies published in patients with a diagnosis of schizophrenia. The diversity of criteria and methods used significantly limits the conclusions that can be drawn. After a comprehensive review of the literature on this topic, the authors have come to the conclusion that there are two opposite trends: 1) Cognition in schizophrenia follows a progressive decline over the years of evolution of the disease (a conclusion predominant in studies with cross-sectional methodology) and 2) Cognition in schizophrenia remains stable once it appears during the first stages of the disease (a conclusion predominant in longitudinal studies). The authors conclude that the question about the likely decline of cognition in schizophrenia cannot be answered due to the lack of rigorous and thorough follow-up studies.