Course of depression in a 10-Year prospective study: Evidence for qualitatively distinct subgroups

The course of depressive disorders can vary considerable, with some individuals exhibiting a chronic course and poor outcomes, while others have a more episodic course and better outcomes. However, it is unclear whether degree of chronicity is continuous or reflects qualitatively distinct subgroups. Using data from a 5-Wave, 10-Year, naturalistic study of 127 depressed outpatients, we examined whether depression chronicity lies on a continuum or manifests natural boundaries. Spline regression was used to test 7 continuous and discontinuous models of the relationship between depression during the first Follow-Up interval and multiple outcomes at subsequent Follow-Ups. In order to further validate the findings, we also created empirically derived subgroups based on the results of the spline regression analyses and compared them on baseline clinical characteristics and Long-Term outcomes. There was a clear and consistent discontinuity indicating that for higher levels of chronicity during the first 30-Month period, depression was linearly related to outcome; in contrast, for lower levels of chronicity, depression in the initial interval was unrelated to subsequent outcomes. The findings were strikingly consistent across the 4 Follow-Up evaluations using multiple outcomes and Goodness-Of-Fit indices. In addition, the chronic Group-As defined by the first Follow-Up Period-Exhibited more baseline chronic depression, anxiety and personality disorders, family history of dysthymia, and childhood adversity, and was more likely to attempt suicide and be hospitalized during Follow-Up, than the nonchronic group. Results suggest that there are qualitatively distinct classes of patients with more and less chronic depressions, and support the utility of longitudinal course as a means of parsing depression into more homogeneous subgroups. General Scientific Summary: Depression can assume a variety of course patterns, ranging from a brief episode to a chronic condition that persists for decades. However, it is unclear whether variations in course are continuous or reflect qualitatively distinct subgroups. Our findings indicate that there are qualitatively distinct classes of chronic and nonchronic depressions that differ on a range of risk factors and Long-Term outcomes.