Wearable-Based Assessment for Relapse Prediction Following Repetitive Transcranial Magnetic Stimulation for Depression: Protocol for a Feasibility Study (WARN-D Study).

BACKGROUND: A significant proportion of patients with major depressive disorder do not achieve remission after 2 antidepressant trials and are considered to have treatment-resistant depression (TRD). Repetitive transcranial magnetic stimulation (rTMS) is an effective treatment for TRD. However, relapse rates among remitters within the first year post treatment are significant, and there are no validated markers of relapse. Wearable devices have shown positive results for longitudinal monitoring of health metrics, and may be a promising tool for early detection of relapse following rTMS treatment. OBJECTIVE: This study aims to evaluate the feasibility of a wearable device (Oura Ring) to monitor individuals receiving rTMS treatment for depression. We will also explore the utility of wearable-derived data as preliminary markers of treatment response and depressive relapse in a 6-month follow-up period. METHODS: This single-arm pilot study will recruit 25 outpatients with a major depressive episode receiving rTMS at 2 tertiary hospitals in Ontario, Canada. Participants will be required to use a smart ring throughout the treatment course and during the 6-month follow-up. Clinical assessments including the Montgomery-Åsberg Depression Rating Scale (MADRS), Patient Health Questionnaire-9 (PHQ-9), Generalized Anxiety Disorder-7 (GAD-7), Insomnia Severity Index (ISI), Posttraumatic Stress Disorder Checklist for DSM-5 (PCL-5), and World Health Organization-Five Well-Being Index (WHO-5) will be collected at baseline, treatment end, and 3- and 6-month follow-ups, alongside biweekly PHQ-9 and GAD-7 scores. The primary outcomes will be defined by feasibility measures (ie, recruitment, adherence, retention, missing data, and usability). Exploratory outcomes will include the assessment of preliminary associations between wearable-derived features and clinical outcomes and depressive relapse. RESULTS: The study was funded in December 2025, and data collection will commence following research ethics approval. At the time of manuscript submission, the study protocol was under review at the Research Ethics Board of the participating institutions, and no study-related activities, including participant recruitment, had started. Data analysis and dissemination of findings will occur following completion of data collection. CONCLUSIONS: This study will provide initial evidence on the feasibility and utility of wearable-based digital phenotyping in individuals receiving rTMS for TRD. Our findings will inform the design of future large-scale studies aimed at wearable-supported relapse prevention and precision monitoring in depression care.