Depression and personality disorder.

Research into the relationship between depression and personality disorder is compromised by a number of methodologic factors, including differing concepts of personality disorder, the validity of a personality disorder diagnosis, the effect of mood on diagnosis, and the overlap between some personality disorder symptoms and mood symptoms. Personality pathology is common in patients with personality disorder. Reasons for this include a "scar" effect of chronic low mood on attitudes and behaviors, as well as possible risk factors via certain personality traits. The negative effect of comorbid personality disorder on treatment outcome in depressed patients may be less than previously believed. Possible reasons include treatment bias in non-controlled trials and the increasing use of selective serotonin reuptake inhibitors rather than tricyclic antidepressants. Many personality traits and disorders may be part of the psychopathology of depression and share a common origin.