The influence of severity of personality disorder on outcome of depression is unclear. Four hundred and ten patients with depression in 9 urban and rural communities in Finland, Ireland, Norway, Spain and the United Kingdom, were randomised to individual problem-solving treatment (n = 121), group sessions on depression prevention (n = 106) or treatment as usual (n = 183). Depressive symptoms were recorded at baseline, 6 and 12 months. Personality assessment was performed using the Personality Assessment Schedule and analysed by severity (no personality disorder, personality difficulty, simple personality disorder, complex personality disorder). Complete personality assessments were performed on 301 individuals of whom 49.8% had no personality disorder; 19.3% had personality difficulties; 13.0% had simple personality disorder; and 17.9% had complex personality disorder. Severity of personality disorder was correlated with Beck Depression Inventory (BDI) scores at baseline (Spearman's r = 0.21; p < 0.001), 6 months (r = 0.14; p = 0.02) and 12 months (r = 0.21; p = 0.001). On multi-variable analysis, BDI at baseline (p < 0.001) and type of treatment offered (individual therapy, group therapy, treatment as usual) (p = 0.01) were significant independent predictors of BDI at 6 months. BDI at baseline was the sole significant independent predictor of BDI at 12 months (p < 0.001). There was no interaction between personality disorder and treatment type for depression.
While multi-variable analyses indicate that depressive symptoms at baseline are the strongest predictor of depressive symptoms at 6 and 12 months, the strong correlations between severity of personality disorder and depressive symptoms make it difficult to establish the independent effect of personality disorder on outcome of depression.