The Impact of Borderline Personality Features on Mood Disorders

Bipolar disorder (BD) and borderline personality disorder (BPD) are complex psychiatric conditions that share notable symptom overlap. Both disorders include transdiagnostic features such as affective instability, impulsivity, and mood dysregulation. These shared symptoms complicate differential diagnosis, particularly regarding emotional instability and impulsive behaviors. Despite these similarities, BD and BPD differ substantially in their underlying mechanisms and standard treatment approaches. BD is marked by episodic mood changes, ranging from depressive episodes to manic or hypomanic states, whereas BPD is characterized by pervasive emotional dysregulation, impulsivity, unstable interpersonal relationships, and a fluctuating sense of self. Typically, BD is treated with pharmacological interventions such as mood stabilizers and antipsychotics, while BPD is primarily addressed through structured psychotherapies, including dialectical behavior therapy (DBT) and cognitive-behavioral approaches. However, there is no standardized psychological intervention specifically designed for BD patients and comorbid borderline personality features (BPF), leaving a significant gap in treatment options for this subgroup.

This thesis aimed to address this gap by examining the utility of Systems Training for Emotional Predictability and Problem Solving (STEPPS), a structured cognitive-behavioral group intervention originally developed for BPD, for patients with BD and comorbid BPF. The primary goal was to determine whether STEPPS could enhance emotional regulation, decrease mood instability, and improve overall quality of life in this population. A secondary objective of this thesis was to explore the broader impact of personality disorders (PDs), particularly BPD features, within BD and major depressive disorder (MDD) populations. To achieve this, data from three sources, the STEPPS study, the Stanley Foundation Bipolar Network (SFBN), and the Netherlands Study of Depression and Anxiety (NESDA), were analyzed to assess the prevalence and influence of PDs in BD.

The initial STEPPS study was designed as a randomized controlled trial (RCT) comparing STEPPS plus treatment as usual (TAU) with TAU alone. Due to lower-than-anticipated recruitment, the design was revised into an open feasibility study. Results showed notable short-term improvements in BD symptoms, patient empowerment, and overall quality of life immediately after treatment. However, these gains diminished over time, with reductions in symptom improvement at the six-month follow-up. This pattern suggests that STEPPS may offer short-term benefits for BD patients with BPF, but that maintenance of these effects may require additional booster sessions. Yet, because of the absence of a control group and the small sample size, firm conclusions regarding STEPPS’ effectiveness cannot be drawn. Nonetheless, the findings provide preliminary support for the idea that structured psychological interventions may be beneficial for BD patients exhibiting BPF, warranting further systematic investigation.

Beyond evaluating STEPPS, the thesis examined the prevalence and consequences of personality pathology across the three cohorts of individuals with mood disorders. In the STEPPS cohort, 70.3% of BD participants screened positive for at least one PD. Data from the SFBN cohort demonstrated that affective instability, impulsivity, and self-harm behaviors predicted more severe and frequent mood episodes, underscoring the importance of targeted interventions that directly address these traits. Findings from the NESDA cohort additionally revealed a strong association between childhood trauma, particularly emotional neglect, and the presence of BPF among individuals with BD.

In conclusion, this thesis offers initial evidence that structured psychotherapeutic interventions such as STEPPS may hold promise for BD patients with BPF, although further refinement and research are required. While implementing structured psychological programs in this population presents challenges, the findings highlight the importance of developing personalized interventions that address the unique clinical needs of BD patients. With continued research and program development, psychological treatments may become a valuable complement to pharmacotherapy, supporting a more integrated and holistic approach to BD and MDD management.