Severity and chronicity appear to contribute additively to functional impairment in depression.52 Thus, DD is associated with as much or more impairment as nonchronic major depression, and double depression is associated with greater impairment than either dysthymia or nonchronic depression.52,53 The impairment is evident in many areas, including work functioning and marital, family, and social relationships. Importantly, there continues to be significant impairment even after recovery.54

Course and Suicide

Not surprisingly, prospective longitudinal studies indicate that persons with chronic depression experience a poorer course than those with episodic depression. For example, in their 10-year follow-up, Klein et al.21 found that patients with persistent depression were symptomatic for 66% of the follow-up period compared to 23% for patients with episodic MDD. Compared to individuals with nonchronic depression, those with persistent depression are significantly more likely to have a history of suicide attempts27,55 and to attempt suicide in the future.21

Most importantly, the chronic versus nonchronic distinction appears to be relatively stable over time. In their 10-year follow-up, Klein et al.21 defined a stable chronic course as no more than 6 consecutive months without threshold or subthreshold depression throughout follow-up and a stable episodic course as full recovery from the index episode within 24 months and no subsequent episode of chronic depression. They found that patients with DD and double depression were 14 times more likely to exhibit a chronic course than were patients with nonchronic major depression. Conversely, patients with nonchronic major depression were 12 times more likely to exhibit a nonchronic depressive course than were patients with DD and double depression.21

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