MRI-guided dmPFC-rTMS as a Treatment for Treatment-resistant Major Depressive Disorder

Summary

Here we outline the procedure for MRI-guided repetitive transcranial magnetic stimulation to the dorsomedial prefrontal cortex as an experimental treatment for major depressive disorder.

Abstract

Here we outline the protocol for magnetic resonance imaging (MRI) guided repetitive transcranial magnetic stimulation (rTMS) to the dorsal medial prefrontal cortex (dmPFC) in patients with major depressive disorder (MDD). Technicians used a neuronavigation system to process patient MRIs to generate a 3-dimensional head model. The head model was subsequently used to identify patient-specific stimulatory targets. The dmPFC was stimulated daily for 20 sessions. Stimulation intensity was titrated to address scalp pain associated with rTMS. Weekly assessments were conducted on the patients using the Hamilton Rating Scale for Depression (HamD₁₇) and Beck Depression Index II (BDI-II). Treatment-resistant MDD patients achieved significant improvements on both HAMD and BDI-II. Of note, angled, double-cone coil rTMS at 120% resting motor threshold allows for optimal stimulation of deeper midline prefrontal regions, which results in a possible therapeutic application for MDD. One major limitation of the rTMS field is the heterogeneity of treatment parameters across studies, including duty cycle, number of pulses per session and intensity. Further work should be done to clarify the effect of stimulation parameters on outcome. Future dmPFC-rTMS work should include sham-controlled studies to confirm its clinical efficacy in MDD.

Introduction

Repetitive transcranial magnetic stimulation (rTMS) is a form of indirect focal cortical stimulation. rTMS employs brief, focal electromagnetic field pulses that penetrate the skull to stimulate target brain regions. rTMS is thought to engage the mechanisms of synaptic long-term potentiation and long-term depression, thereby increasing or decreasing the cortical excitability of the region stimulated¹. Generally, the rTMS pulse frequency determines its effects: higher frequency stimulation tends to be excitatory, while lower frequency is inhibitory. Non-invasive stimulatory procedures are also widely used as a causal probe to induce temporary ‘cortical....

Protocol

This study was approved by the Research Ethics Board at the University Health Network.

1. Subject Selection

1. Conduct an initial assessment on a prospective patient. The inclusion criteria included the presence of a current depressive episode that is resistant to at least 1 adequate trial of medication, and a Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, (DSM-5) diagnosis of MDD as established by the assessing psychiatrist. Confirm the diagnosis with a standardized Mini Mental State Examination (MINI).
2. Ensure that patients are on a stable medication or are washed out of their medication routine fo....

Results

In previous work, HamD₁₇ was used as a measure of treatment response for 10 Hz dmPFC-rTMS. Table 1 displays the pre- and post-treatment HamD₁₇ scores in a previously published case series²⁷. Among all subjects, pre-treatment HamD₁₇ score was 21.66.9 that significantly decreased by 4,331% to 12.58.2 post-rTMS (t₂₂ = 6.54, p <0.0001)²⁷. Using a remission criterion of HamD₁₇ ≤7, 8 of 23 subjects remitted following treatme.......

Discussion

Here, MRI-guided dmPFC-rTMS was applied for treatment-resistant MDD. In general, rTMS at this site was well tolerated, with mild scalp discomfort and pain at the site of stimulation that was adequately managed using adaptive titration. In open-label trials and a chart review, both 10 Hz and theta burst stimulation resulted in significant improvements in depressive severity as measured by the HamD₁₇ and BDI-II.

There are two critical steps worth noting in the rTMS treatment procedure.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3T GE Signa HDx Scanner	GE	n/a
Visor 2.0 Neuronavigation System	ANT Neuro	n/a
MagPro R30 Stimulator	MagVenture	n/a
Cool-DB80 Coil	MagVenture	n/a