Epidemiology of subtypes of depression

Objective: There is a general clinical impression that depression differs qualitatively from non-depressive conditions, and that it can be identified as a categorical entity. In contrast, epidemiological studies support the view that depression is dynamic in nature and develops on a continuous scale. The present article reviews selected epidemiological studies of depressive subtypes. Method: A selective review. Results: Prior studies have found no clear differences in clinical presentation or long-term outcome between patients with melancholic and with neurotic/reactive depression. In addition, recent studies suggest that there is no clear demarcation between mild, moderate, and severe depression, pointing toward a continuity rather than categories of illness. For the individual patient, depressive symptoms seem to change over time, fulfilling criteria for major depression, minor depression, dysthymia, and subsyndromal states; the association between stressful life events and depression appears to diminish with the number of depressive episodes. Finally, recent genetic findings are congruent with a model indicating that the majority of depressions develop in the interplay between genes and stressful experiences, whereas 'reactive' depressions and 'endogenous' depressions apparently exist at a lower prevalence. Conclusion: Further longitudinal, analytical, and genetic epidemiologic studies are needed to reveal which conditions are mild and transient, and which may be precursors of more severe and substantial illness such as melancholia.