Repetitive Transcranial Magnetic Stimulation for Depression: State of the Art.

Abstract

Byline: M. Reddy, M. Vijay Electroconvulsive therapy (ECT) which was introduced in the early 20[sup]th century, enjoyed an unsurpassed position among the neuromodulation treatments for mood disorders until recently, but that is being challenged by a newer neuromodulation technique called repetitive transcranial magnetic stimulation (hereafter, rTMS). rTMS utilizes magnetic pulses to influence the excitability and connection strength of the cortical neurons. In this article, we will review relevant research on the efficacy, mechanism of action, procedure, responsibility of treating physician, clinical recommendations, safety, etc., and comment on the future challenges and opportunities. Efficacy of Repetitive Transcranial Magnetic Stimulation in Depression The neuromodulation treatment with rTMS is sought usually after the failure of one or more antidepressant medications with or without a course of psychotherapy. On the clinical line of management, it comes after the use of medications ([+ or -]psychotherapy) and before planning for ECT. The response rate in major depressive disorder is between 50% and 55% and remission rate between 30% and 35% according to the researchers.[sup][1],[2] In a recent systematic review,[sup][3] the number needed to treat was calculated to be 10. However, in comparison with sham treatments, rTMS had small short-term effect on depression which did not continue for longer periods in the follow-up studies. Comparison studies of rTMS and ECT showed better effectiveness of ECT over rTMS every time and that ECT was cheaper than rTMS in cost.[sup][3],[4] rTMS, on the other hand, had higher patient preference and far less adverse effects compared to ECT.[sup][4] A related neuromodulation treatment is the magnetic seizure therapy (MST). MST also uses magnetic pulses, albeit of a higher frequency than rTMS, to stimulate a specific area in the brain with the aim of inducing a seizure. Researchers have found comparable efficacy between MST and ECT in treatment- resistant depression [sup][5] while MST having lower cognitive side effects.[sup][6] Mechanism of Action in Depression Research on rTMS in depression is also providing insights into its mechanism of action. Functionally, high-frequency stimulation of the left prefrontal cortex and low-frequency stimulation of the right prefrontal cortex leading, respectively, to long-term potentiation and long-term depression of the cortical neurons is related to alleviation of depressive symptoms.[sup][7] This is further supported by instances of high-frequency stimulation of left prefrontal cortex worsening symptoms of patients with mania.[sup][8] Newer research with magnetoencephalography suggests that following changes [sup][9] correlate with improvements in depressive symptoms: *Increase in gamma (a) power at the left dorsolateral prefrontal cortex (L-DLPFC) *Increase in delta (a) band connectivity between L-DLPFC and amygdala and between L-DLPFC and pregenual anterior cingulate cortex *Decrease in gamma (a) band connectivity between L-DLPFC and subgenual anterior cingulate cortex. Procedures, Roles and Responsibilities The interest of clinicians on rTMS is due to its potential use in an office setting without any need for anesthesia or fear of serious adverse effects. Usually, before the actual procedure, patients are asked to remove any magnet-sensitive objects such as chains and credit cards and asked to wear ear plugs as the machine produces loud clicking sounds much like magnetic resonance imaging machine. As the patient is seated on a chair, measurements are made over the scalp to place the coil appropriately. rTMS is usually administered [sup][10] in five daily treatments over 3–6 weeks with the objective of delivering 20–30 sessions in a course of treatment. Each session with the current standard protocol consists of high frequency (i. …