To examine prospectively the natural course of major depressive disorder (MDD) and to test the effects of personality disorders (PDs) on remission and relapse over six- year follow-up.

Subjects were 302 patients (196 women, 106 men) with current MDD at baseline enrollment in the Collaborative Longitudinal Personality Disorders Study (CLPS), a NIMH-funded multi-site study (Yale, Brown, Columbia, Harvard). MDD and psychiatric disorders were assessed with the Structured Clinical Interview for DSM-IV and PDs with the DIPD-IV. The course of MDD was assessed with the Longitudinal Interval Follow-up Evaluation and the course of PDs with the Follow-Along version of the DIPD-IV at 6- and 12-months and then yearly for 6 years. Good inter-rater and test-retest reliabilities were established.

Lifetable survival analyses revealed an overall 24-month remission rate of 74% for MDD that differed little by gender but was significantly lower among patients with PDs (range 52% to 81%) than without PDs (89%). Cox proportional hazards regression analyses revealed that MDD patients with co-existing PDs had significantly longer time to remission than did MDD patients without any PD even when controlling for other negative prognostic predictors (psychiatric co-morbidity, dysthymia, gender, ethnicity, early-onset and recurrent MDD, and treatment). Among patients who achieved remission from MDD, the probability of relapse was significantly greater and time to relapse was significantly shorter in patients with PD than without PD.

PDs are a robust predictor of slowed remission and accelerated relapse in MDD.