Major depression is a common mental health condition and is associated with significant disease burden. Up to a third of individuals suffer from treatment resistant depression (TRD), which is a failure to demonstrate any significant improvement in response to psychological or pharmacological therapies. These individuals are often referred for neurostimulatory interventions such as electroconvulsive therapy (ECT). The field of neurostimulation however has evolved to include several alternative techniques including transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS) and deep brain stimulation (DBS). Whilst some forms of TMS, such as repetitive TMS (rTMS), are already in clinical use, tDCS could provide a method for non-invasive neurostimulation to be self-administered at home. Research into DBS has identified several brain regions, including the subcallosal gyrus, which show promise as therapeutic targets. Further neurostimulation techniques in development include automated closed loop DBS systems in addition to minimally invasive neurostimulator devices. Thus neurostimulation has great potential in reducing the health burden associated with TRD. At time of writing no review has investigated the efficacy of both invasive and non-invasive neurostimulation techniques specifically in TRD. This presentation (review) explores the efficacy of these neurostimulation techniques with the aim of increasing understanding and promoting evidence based use of neurostimulation in the management of TRD.

Method This systematic review, following PRISMA guidelines, analyzed neurostimulation techniques for treating Treatment-Resistant Depression (TRD) in adults. We identified 178 articles on the use of TMS, tDCS, and DBS for the treatment of treatment-resistant depression (TRD). Of these, 79 studies met the inclusion criteria (TMS N=57; tDCS N=4; DBS N=18).

Results Response rates to Transcranial Magnetic Stimulation (TMS) varied from 22% to 88%, with an average response rate of 52%. Similarly, response rates to transcranial direct current stimulation (tDCS) exhibited a range of 18% to 65%, with an average response rate of 35%. Conversely, response rates to deep brain stimulation (DBS) ranged from 40% to 80%, with an average response rate of 62%. Remission rates varied from up to 73% in TMS, to 50% in tDCS and 67% in DBS.

Conclusion Neurostimulation is a rapidly evolving field with the potential to revolutionize the treatment of neuropsychiatric disorders. Though response and remission rates look promising there is significant work to be done on refining the techniques and on the study of long term outcomes.