The trajectory of neuropsychological dysfunctions in bipolar disorders: A critical examination of a hypothesis

Objective The hypothesis of a progressive nature of neuropsychological deficits in bipolar disorders is often accepted as an axiom by many clinicians and researchers in the field. However, contradictory pieces of data and a number of methodological concerns put it under debate. Method We reviewed findings from three different approaches to the study of the trajectory of cognitive features in bipolar disorders: longitudinal evaluation of cognition in affected subjects, cross-sectional neuropsychological assessment of patients belonging to different age groups, and exploration of the risk of dementia in bipolar subjects. Results An increased risk of developing dementia was found in bipolar subjects. However, evidence from cross-sectional studies did not show more severe cognitive deficits in patients with longer illness duration. Furthermore, longitudinal studies revealed that bipolar subjects' cognitive performance did not change between different points in time. Conclusions After a thorough discussion of these findings and the limitations of the different approaches, we argue that, at present, there is no consistent evidence supporting that bipolar disorders, as a group, have a progressively deteriorating course of cognitive functions. Furthermore, we highlight the possible influence of psychotropic agents and metabolic factors on neuropsychological outcomes. Finally, we discuss the clinical implications of these findings and propose targets for forthcoming research.