The effect of comorbid personality disorder on depression outcome after short-term psychotherapy in a randomised clinical trial

BACKGROUND: Time-limited psychotherapy for depression is effective. However, comorbid personality disorders affect therapy outcomes negatively. Studies of follow-up effects and results relating to the influence of comorbid personality disorder and treatment modality are scarce. AIMS: To determine the influence of comorbid personality disorder and treatment modality on outcomes after cognitive–behavioural therapy (CBT) or short-term psychodynamic supportive psychotherapy (SPSP) for depression. METHOD: This study draws on data from a previously published randomised clinical trial contrasting SPSP and CBT for depression (both 16 sessions). We compared the effectiveness of these psychotherapies for patients with and without personality disorder (n = 196). The primary measure was depression outcome; the secondary measurements were interpersonal functioning and quality of life. Collected data were analysed using multilevel analysis. Trial registration: ISRCTN31263312 (http://www.controlled-trials.com). RESULTS: Although participants with and without comorbid personality disorder improved at treatment termination (d = 1.04, 95% CI 0.77–1.31 and d = 1.36, 95% CI 0.97–1.76, respectively) and at follow-up (d = 1.15, 95% CI 0.87–1.43 and d = 2.12, 95% CI 1.65–2.59 respectively), personality disorder had a negative effect on depression outcome at both measurement points (P < 0.05). A similar negative effect on interpersonal functioning was no longer apparent at follow-up. Comorbid personality disorder had no influence on social functioning or quality of life outcomes, irrespective of treatment modality. CONCLUSIONS: CBT and SPSP contribute to the improvement of depressive symptoms and interpersonal problems in depressed patients with and without comorbid personality disorder. Both treatments are an effective first step in a stepped care approach, but – given remaining levels of depression in patients with personality disorder – they are probably inadequate for large numbers of patients with this comorbidity. DECLARATION OF INTEREST: None.