Can Course Help Reduce the Heterogeneity of Depressive Disorders?
DANIEL N. KLEIN
The depressive disorders are clinically and etiologically heterogeneous; thus, information about course may be helpful in parsing this heterogeneity. This chapter considers the role of chronicity, or persistence, in distinguishing different forms of nonpsychotic, non-bipolar depression. First, we briefly summarize rates of recovery in naturalistic follow-up studies and discuss the classification of chronic depression, including support for the Diagnostic and Statistical Manual of Mental Disorders 5th edition’s (DSM-5) decision to combine different forms of chronic depression under the rubric of Persistent Depressive Disorder. Next, we review the evidence indicating that there are consistent clinical and etiological differences between persistent/chronic depression and nonchronic depression. We briefly consider other sources of heterogeneity within chronic depression and then extend the discussion to the role of course in parsing the heterogeneity of subthreshold depression. Finally, we conclude by considering the challenges in defining a chronic depressive spectrum and developing a life span perspective on the course of depression.