Classifying depression: Should paradigms lost be regained?

Objective: Classification of the depressive disorders has long been controversial. The dominant current model is unitarian, with disorders largely distinguished on the basis of severity. Both the unitarian and the contrasting binarian views (of two principal types) have proved to be unsatisfactory. The binarian model's procrustean requirements are too inflexible to address the evident heterogeneity contributed to by clinical manifestations and underlying personality features. Method: This article briefly reviews the historically favored unitarian and binarian viewpoints on classification of depression. Results: The author argues that the final common pathway model, articulated in the early 1970s, helped to cement psychiatric classification in subsequent DSM and ICD revisions into a unitarian framework, leading to a relatively sterile period of depression research. Clinically described depressive typologies were obscured rather than refined by appropriate modeling paradigms. A contrasting, empirically based hierarchical model, driven by disorder-specific clinical manifestations such as psychotic features and observable psychomotor disturbance, is proposed as a paradigm for distinguishing psychotic, melancholic, and nonmelancholic classes of depression, while a spectrum model is favored for distinguishing the principal nonmelancholic subclasses. Conclusions: Resolution of the better paradigm requires that the two models undergo comparative testing in applied studies, particularly ones pursuing neurobiological determinants and differential responses to antidepressant treatments.