How changes in depression severity and borderline personality disorder intensity are linked – a cohort study of depressed patients with and without borderline personality disorder

Background Borderline personality disorder (BPD) is often complicated by comorbid major depressive episodes (MDEs), which can occur as part of major depressive disorder (MDD) or bipolar disorder (BD). Such comorbidity is related to worse outcomes in both disorders. Subsyndromal features of BPD are also common in depression. However, studies of simultaneous changes in BPD and depression severities are scarce, and their interactions are poorly understood. Aims Studying the associations between changes in BPD and depression symptoms over the course of an MDE. Methods In a 6-month naturalistic cohort study of MDE/BPD, MDE/MDD, and MDE/BD patients ( N = 95), we measured change in BPD features between baseline and six months with the Borderline Personality Disorder Severity Index (BPDSI), an interviewer-rated instrument quantifying recent temporal frequency of BPD symptoms. We examined changes in BPD severity and their correlation with depression severity and other clinical measures and compared these across patient groups. Results There were significant reductions in BPD severity, both in number of positive BPD criteria (-0.35, sd 1.38, p = 0.01672) and in BPDSI scores (-4.23, SD 6.74, p < 0.001), reflecting mainly a reduction in temporal frequency of symptoms. These were similar in all diagnostic groups. In multivariate regression models, changes in depression severity independently associated with changes in symptoms in the BDSI. This relationship was strongest in MDE/BPD patients but was not found in MDD patients without BPD. Conclusions In the six-month follow-up, BPD features in MDE patients alleviated mainly by decreasing temporal symptom frequency and intensity. In BPD patients with comorbid MDE, changes in both conditions are strongly correlated.