Seasonal pattern of mood episode onset

**Definition:** In the context of recurrent depressive disorder, bipolar type I or bipolar type II disorder, there has been a regular seasonal pattern of onset and remission of at least one type of episode (i.e., depressive, manic, mixed, or hypomanic episodes), with a substantial majority of the relevant mood episodes corresponding to the seasonal pattern. (In bipolar type I and bipolar type II disorder, all types of mood episodes may not follow this pattern.) A seasonal pattern should be differentiated from an episode that is coincidental with a particular season but predominantly related to a psychological stressor that regularly occurs at that time of the year (e.g., seasonal unemployment).