Major depressive disorder

Major depressive disorder or "unipolar depression" is a common condition likely related to several etiologies. Recent research has focused on the biological underpinnings of major depressive disorder as well as treatment advances, involving both pharmacotherapy and psychotherapy. In this chapter, the epidemiology, clinical picture, biological theories regarding etiology, clinical presentation in primary care and mental health settings, and treatment of major depressive disorder are reviewed. Advances in genetic approaches to understanding the pathogenesis of major depressive disorder will likely result in better and more precise treatments in the future. The term "unipolar depression" evolved from the concept of a primary affective disorder. Primary affective disorder referred to patients whose first psychiatric disorder was depression and who did not evidence manic or bipolar symptoms. Support for the classification of primary affective disorder derived from the classic study of Cassidy et al (1), and symptoms differentiating depressed patients from controls formed the basis of the disorder. Symptoms which occurred in more than 50% of depressed patients included reduced energy, impaired concentration, anorexia, initial insomnia, loss of interest, difficulty starting activities, worrying, subjective agitation, slowed thinking, difficulty making decisions, terminal insomnia, suicidal ideation or plans, weight loss, tearfulness, slowed movements, irritability, and feeling one will never get well (2). These symptoms continue to form the basis for the diagnosis of depressive states.