Objectives: Treatments for borderline personality disorder (BPD) and post-traumatic stress disorder (PTSD) are less effective for patients with co-occurring symptoms of both disorders, who are considered to have complex PTSD (cPTSD), compared with patients with either condition alone. Evidence suggests that co-occurrence of symptoms indicates greater impairment in mentalizing. This study examines evidence for targeting mentalizing when treating individuals with co-occurring symptoms, irrespective of their exposure to developmental trauma and, for the first time, investigates the mediational role of mentalizing in the associations between BPD symptomatology and cPTSD.

Design: We identified in a routine clinical service a group of patients with BPD, with or without co-occurring symptoms of PTSD. We hypothesized that patients with co-occurring symptoms and a history of childhood maltreatment will show more severe clinical profiles and greater mentalizing problems, which in turn lead to symptoms consistent with cPTSD.

Method: Clinical profiles of 72 patients with BPD (43 with and 29 without co-occurring symptoms of PTSD; mean age in both groups 28 years, 79% and 83% female, respectively) were identified using the Structured Clinical Interview for DSM-IV Axis II Disorders. Patients completed self-report measures of BPD and PTSD symptoms, well-being, dissociation and reflective functioning. Childhood trauma histories were evaluated.

Results: Compared with patients with BPD-only, those with co-occurring BPD and PTSD showed greater severity in terms of BPD and dissociative symptoms, met a broader range of BPD diagnostic criteria, had a greater sense of personal worthlessness and self-evaluated their well-being as considerably diminished. This group was also more inclined to recall increased instances of childhood sexual abuse. In a mediation analysis, mentalizing acted as a partial mediator for the relationship between BPD severity and cPTSD, as well as between dissociative symptoms and cPTSD. Interestingly, mentalizing did not mediate the relationship between childhood sexual abuse and cPTSD.

Conclusions: Overall, the correlational findings are consistent with an intended focus on mentalizing to treat cPTSD symptoms in individuals who also meet criteria for a diagnosis of BPD.