Effect and neural mechanisms of the transcutaneous vagus nerve stimulation for relapse prevention in patients with remitted major depressive disorder: protocol for a longitudinal study.

INTRODUCTION: After the first episode, patients with remitted major depressive disorder (MDD) have a 60% chance of experiencing a second episode. There are currently no accepted, effective methods to prevent the recurrence of MDD in remission. Transcutaneous vagus nerve stimulation (taVNS) is a non-invasive, safe and economical approach based on the efficacy of VNS in improving clinical depression symptoms. This clinical trial will study the efficacy of taVNS in preventing MDD relapse and investigate the underlying mechanisms of this. METHODS AND ANALYSIS: We will conduct a multicentre, randomised, patient-blinded and evaluators double-blinded trial. We will randomise 90 eligible participants with recurrent MDD in remission in a 1:1 ratio into a real or sham taVNS group. All participants will be given six biopsychosocial assessments: proinflammatory cytokines, serum monoamine neurotransmitters, cognition, affective neuropsychology, multimodal neuroimaging and endocrinology. After the baseline measurements, all participants will be given corresponding interference for 6 months and then complete a 1-year follow-up. The assessments will be performed three times: at baseline, post-treatment and at the end of 1-year follow-up (except for multimodal MRI scanning, which will be conducted at the first two assessments only). Change in 17-item Hamilton Depression Rating Scale scores for MDD is the primary outcome parameter. ETHICS AND DISSEMINATION: The study protocol was approved by the Medical Ethical Committee of Beijing Hospital of Traditional Chinese Medicine on 18 January 2019 (2018BL-076). The trial results will be published in peer-reviewed journals and at conferences. TRIAL REGISTRATION NUMBER: ChiCTR1900022618.