Immune-inflammatory markers of response to repetitive transcranial magnetic stimulation in depression: A scoping review

Repetitive transcranial magnetic stimulation (rTMS) is a safe, effective and non-invasive form of neuromodulatory therapy in patients with major depressive disorder (MDD). MDD is associated with increased peripheral and brain inflammation. The current paper aims to provide an overview of research examining the relationship between immune and inflammatory markers and response to rTMS in MDD. A scoping review method was adopted in keeping with the PRISMA-ScR guidelines. Twelve relevant studies were retrieved from the PubMed and Scopus databases and rated for study quality using a modified version of the BIOCROSS tool. Response to rTMS in MDD was associated with basal and post-treatment levels of the inflammatory markers amyloid A, antithrombin III, oxidised phosphatidylcholine, and the microRNA miR-146a-5p. Inconsistent results were observed for the cytokines interleukin-1β, interleukin-2 and tumour necrosis factor-α. Increased baseline levels of interleukin-6 and C-reactive protein were linked to a poorer response to rTMS. These results suggest that rTMS may have effects on immune-inflammatory pathways that are distinct from those of antidepressants and electroconvulsive therapy. Because of certain methodological limitations in the included studies, these results should be interpreted with caution.