Objective: It is a widely held belief that affective disorders are progressive of nature; however, some recent reviews have questioned this belief. The objective of the present systematic literature review was to present evidence for associations between number of affective episodes and (i) the risk of recurrence of episodes, (ii) probability of recovery from episodes, (iii) severity of episodes, (iv) the threshold for developing episodes, and (v) progression of cognitive deficits in unipolar and bipolar disorders.
Method: A systematic review comprising an extensive literature search conducted in Medline, Embase, and PsychInfo up to September 2016 and including cross-references from identified papers and reviews.
Results: Most of the five areas are superficially investigated and hampered by methodological challenges. Nevertheless, studies with the longest follow-up periods, using survival analysis methods, taking account of the individual heterogeneity all support a clinical progressive course of illness. Overall, increasing number of affective episodes seems to be associated with (i) increasing risk of recurrence, (ii) increasing duration of episodes, (iii) increasing symptomatic severity of episodes, (iv) decreasing threshold for developing episodes, and (v) increasing risk of developing dementia.
Conclusion: Although the course of illness is heterogeneous, there is evidence for clinical progression of unipolar and bipolar disorders.