A general clinical assumption states that cluster B personality disorders (PDs) represent a more severe form of PD than cluster C PDs. Consequently, most PD research is centered on cluster B PDs (especially borderline PD). Yet, prevalence ratings of cluster C PDs exceed those of cluster B PDs. In this explorative, cross-sectional study, we compared cluster B and C PD patients (N = 94) on a wide range of clinically-relevant severity measures, including comorbidity, suicidality, (childhood) traumatization and global functioning. Results showed that, although cluster B PD patients suffered more often from substance use disorders and lifetime suicide attempts, no difference could be established between groups for all other severity measures, including trauma variables. In our study, we additionally included a group of combined cluster B and C PDs, who were largely similar to both other groups. Although our study is insufficiently powered to claim a significant non-difference, these findings emphasize that high rates of comorbidity, suicidality, childhood traumatization and functional impairment apply to both cluster B and C patients. As such, our findings encourage more research into cluster C PDs, ultimately leading to more evidence-based treatments for this prevalent patient group. In addition, the high level of traumatization across groups calls for a routine trauma screening, especially since PD treatment may benefit from concurrent trauma treatment.

Background: Borderline personality disorder (BPD) is often associated with insomnia, which may contribute to a vicious cycle of reciprocal exacerbation of sleep disturbance and BPD symptoms. Online cognitive behavioral therapy for insomnia (iCBT-I) has shown promise for treating insomnia in BPD patients. This study evaluated the key determinants, underlying processes, and change mechanisms of successful implementation of guided iCBT-I in BPD patients. Methods: In the context of our clinical trial, we conducted this mixed-method process evaluation in 30 patients with BPD and comorbid insomnia complaints (mean age 29.5 years ± 8.72) that received guided iCBT-I. Our process evaluation was guided by four dimensions of the theoretical RE-AIM framework: Reach (e.g., reason participation), Effectiveness (e.g., perceived symptom reduction), Implementation (e.g., treatment delivery), Maintenance (e.g., sustained adherence). We combined insights from quantitative patient-reported evaluation of treatment satisfaction and adherence and therapist log data, with qualitative exploration of patient experiences through in-depth interviews in a subsample of five patients. Results: 21 patients (70%) completed the intervention. Patients appreciated the online modality and emphasized the importance of responsive and personalized (videocall) therapist guidance and active reminders. Patients found behavioral strategies, such as fixed bedtimes and an evening winding-down routine particularly helpful, while more introspective and cognitive techniques were often perceived as challenging. Qualitative effectiveness evaluations aligned with clinical trial outcomes on BPD, insomnia and arousal-related symptoms. Finally, patients expressed a strong desire for more and well-integrated sleep treatment into regular BPD care trajectories. Conclusions: Guided iCBT-I proved a feasible and promising intervention for patients with BPD, with successful implementation contingent upon personalized guidance, focus on behavioral strategies tailored to individual needs, and solid integration into BPD care.