Contributors of Functional Impairment in Major Depressive Disorder: a Biopsychosocial Approach

Abstract

This narrative review summarizes the current evidence regarding functional impairment in MDD and the factors contributing to it. Major depressive disorder (MDD) is a leading cause of disability and is associated with substantial economic burden, largely due to the functional impairment common among MDD patients. Despite the prevalence of functional impairment in MDD, it has not typically been investigated as a primary treatment outcome in MDD until recently, as treatment studies have largely focused on symptoms. Notably, studies consistently demonstrate the divergent trajectories of improvement of depression symptoms and functional impairment. Furthermore, the most consistent findings point to MDD symptom severity, cognitive deficits, sleep, fatigue, low energy, and social isolation as key contributors to functional outcomes in MDD. There is currently a paucity of data regarding neurobiological mechanisms of functional impairment. The findings from published literature are organized into a proposed working biopsychosocial model of functional impairment in MDD that highlights the strengths and existing research gaps in the field. The implications of these findings on depression treatment strategies are also discussed. Our proposed biopsychosocial model of functioning in depression may serve to define an individual’s “functional impairment profile,” which can be used to identify targeted and personalized treatments for depression, and lead to improved outcomes.