Factors for predicting response to electroconvulsive therapy (ECT), transcranial magnetic stimulation (TMS) and ketamine in patients with treatment-resistant depression: a systematic review

BACKGROUND: Treatment-resistant depression (TRD) remains a complex challenge, often requiring interventions beyond standard medications. This review explores factors that may predict positive response to electroconvulsive therapy (ECT), repetitive transcranial magnetic stimulation (rTMS) and ketamine-based treatments to help guide clinical decision-making. METHODS: A systematic review was conducted following PRISMA 2020 guidelines. English-language, peer-reviewed studies were identified through PubMed, Embase and Google Scholar using search terms such as 'treatment-resistant,' 'outcome,' 'prediction,' 'ECT,' 'rTMS,' and 'ketamine.' Studies were included if they examined clinical, biological or imaging predictors of response in adults with TRD. Case reports, reviews, editorials and non-English articles were excluded. A total of 42 studies were selected from 408 screened. RESULTS: Among these, 23 focused on ketamine/esketamine, 14 on rTMS, and 11 on ECT. Predictive factors were grouped into clinical (e.g., symptom profile, illness duration), biological (e.g., IL-6, CRP, BDNF) and imaging (e.g., cingulate cortex activity, connectivity). Inflammation markers and fronto-limbic network findings appeared across treatments, though findings were inconsistent. DISCUSSION: While some predictors show promise, clinical use remains limited by methodological differences and small sample sizes. Larger studies are required to identify clinically useful predictors. Additionally, for optimal treatment decision-making, comparative studies are necessary.