Enhanced home-based transcranial direct-current stimulation (tDCS) for depression comorbid with borderline personality disorder (BPD): study protocol for a pilot double-blinded randomised controlled trial (TENTADIS).

introductionMajor depressive disorder (MDD) is the most common comorbidity among individuals with borderline personality disorder (BPD), affecting over 85% of patients and leading to high recurrence rates and resistance to treatment. Traditional pharmacological and psychotherapeutic interventions often show limited efficacy in this population, highlighting the need for innovative treatment strategies. Emerging evidence suggests that the dorsolateral prefrontal cortex (DLPFC) plays a crucial role in the pathophysiology of both MDD and BPD. In addition, non-invasive brain stimulation, particularly transcranial Direct Current Stimulation (tDCS), has shown promising results in alleviating depression and improving BPD symptoms when targeting the DLPFC. The development of home-based tDCS presents new opportunities for accessible and cost-effective interventions. However, no study has specifically investigated its effects on MDD in the context of BPD. METHODS AND ANALYSIS: This double-blind randomised controlled trial will assess the feasibility and explore the efficacy of home-based tDCS in reducing depressive symptoms in BPD patients who are experiencing moderate to severe depressive episodes. A total of 60 participants will be randomised, following a 2-week online psychoeducation, to receive either active or sham tDCS in 14 sessions over 1 week. The primary outcome is the feasibility of home-based tDCS in remote and urban areas. The secondary aim is to obtain a preliminary assessment of the efficacy of 14 home-based tDCS sessions in reducing depressive symptoms in BPD patients with moderate to severe depressive episodes and BPD symptoms. Exploratory analyses will evaluate the impact of tDCS on neuropsychological functioning, physical activity and substance use. Sociodemographic variables will be considered in predicting treatment response. All assessments will be conducted at baseline, post-treatment and during follow-ups through 3 months after treatment ends. ETHICS AND DISSEMINATION: This study has received approval from the Research Ethics Committee of the Centre intégré universitaire de santé et de services sociaux de l'Est-de-l'Île-de-Montréal (CIUSSS-EMTL) (approval number: MP-12-2025-4050). All participants will provide informed consent prior to inclusion. Findings will be disseminated through peer-reviewed publications, conference presentations and knowledge translation activities targeting clinicians, researchers and mental health stakeholders. TRIAL REGISTRATION NUMBER: NCT06972368.