Supplementary Material for: Eye Movement Desensitisation and Reprocessing with and without Dialectical Behaviour Therapy for Posttraumatic Stress Disorder and Comorbid Borderline Personality Disorder Symptoms: A Randomised Controlled Trial

Introduction: Comorbidity between posttraumatic stress disorder (PTSD) and borderline personality disorder (BPD) is prevalent. Despite evidence-based therapies, high rates of non-response and dropout persist. This study therefore aimed to examine whether the concurrent application of eye movement desensitization and reprocessing (EMDR) for PTSD and dialectical behavior therapy (DBT) for BPD yields better results than EMDR alone. Methods: Patients with a PTSD diagnosis and at least four BPD symptoms were randomly assigned to EMDR (n = 63) or concurrent EMDR-DBT (n = 61). Over one year, changes in PTSD symptoms were measured using the Clinician-Administered PTSD Scale for DSM-5. Secondary outcomes included BPD symptoms, global functioning and quality of life. Results: Both treatments led to large reductions in PTSD symptoms, without significant differences after one year (p = .312, d = -0.23, 95% CI = -0.6, 0.1). Both treatments also yielded large and comparable reductions in BPD symptoms and improved quality of life. Global functioning improved only in the EMDR condition according to one measure (WHODAS 2.0), while the other measure (OQ-45) showed improvements in both groups. Additionally, patients in the EMDR-DBT condition were twice as likely to drop out from EMDR treatment compared to those in the EMDR-only condition. Conclusion: Stand-alone EMDR demonstrated safety and efficacy in alleviating PTSD and BPD symptoms, as well as enhancing quality of life. These findings support the use of EMDR as a strong therapeutic option for patients with PTSD and comorbid BPD symptoms. Further research is needed to assess longer-term outcomes beyond one year.