Management of Treatment-Resistant Depression _ _________________________________________________ VAGUS NERVE STIMULATION
TRANSCRANIAL MAGNETIC STIMULATION
Vagus nerve stimulation uses an implantable device to provide intermittent stimulation to the left vagus nerve (80% afferent to the central nervous system) [2]. It received FDA approval for treatment-resistant depression in 2005 due to the lack of approved drug treatments and concerns over the long-term efficacy and safety of ECT [31]. Controlled studies with follow-up six months or longer have found significant improvements in depressive symptoms that were often sustained over time, with relapse rates relatively low [32]. Long-term vagus nerve stimulation can lead to significant side effects, including decreases in airway flow and respiratory effort and laryngopharyngeal dysfunction [33]. Given the pro- found negative impact of treatment-resistant depression and lack of durable response in some patients, vagus nerve stimula- tion may be a useful option [34]. In a 2017 trial, patients with treatment-resistant MDD and four or more failed depression treatments (including ECT) received vagus nerve stimulation or treatment as usual and were followed five years. Response was a ≥50% decrease in MADRS score at any follow-up visit. Subjects who received vagus nerve stimulation (compared with usual treatment) had more severe treatment-resistant depression on several dimensions [35]. Vagus nerve stimula- tion led to greater five-year cumulative response (67.6%) and remission (43.3%) rates compared with usual treatment (40.9% and 25.7%, respectively). However, vagus nerve stimulation response often required 12 or more months to appear [35]. Guidelines recommend against the use of vagus nerve stimula- tion outside a research setting [23]. DEEP BRAIN STIMULATION With deep brain stimulation, an electrode is surgically implanted to stimulate the subgenual cingulate gyrus with high-frequency impulses to reduce depressive symptoms [2]. Deep brain stimulation is invasive and carries the risk of infection, hemorrhage, and other surgical complications. Stimulation-induced adverse effects such as facial contractions, facial paresthesias, olfactory phenomena, anxiety, and mood fluctuations have been reported, particularly at higher levels of stimulation [36]. Most clinical improvement shows delayed onset; one trial in patients with treatment-resistant depression reported remission rates of 27%, 24%, and 37% at three-month, six-month, and two-year follow-up, respectively [37]. Deep brain stimulation can increase the risk of suicide ideation, attempts, and death, strongly indicating that patients should be pre-screened for suicide risk and monitored closely for suicidal behavior pre- and postoperatively [38]. Deep brain stimulation is investigational for treatment-resistant depression and is reserved for use in patients with severe refractory psychiatric, neurologic, or chronic pain conditions [21; 36].
Repetitive transcranial magnetic stimulation delivers high- intensity magnetic pulses to the cortex through a stimulating coil placed to the forehead [39; 40]. It is a first-line MDD treat- ment in patients with one or more failed antidepressant trial [21]. Efficacy in treatment-resistant depression was established using stringent criteria; analysis of 23 trials found significantly greater efficacy and effect size for repetitive transcranial mag- netic stimulation over sham [41]. In randomized clinical trials, 20 to 30 sessions over four or more weeks achieved 40% to 55% response and 25% to 35% remission rates [42]. The most frequent side effects are transient scalp pain (40%) and headache (30%). Both diminish with repeated treatment and respond to over-the-counter analgesics. The cognitive safety profile is benign. Seizures are the most serious side effect, but fewer than 25 cases have been reported worldwide [21; 43]. Repetitive transcranial magnetic stimulation is contraindicated in patients with any metal or metallic hardware in the head (except the mouth), with a history of seizures, and who take medications that lower seizure threshold [21; 44].
For patients who have demonstrated partial or no response to two or more adequate pharmacologic treatment trials, the U.S. Department of Defense/ Veterans Affairs (DoD/VA) suggests offering repetitive transcranial magnetic
stimulation for treatment. (https://www.healthquality.va.gov/guidelines/MH/ mdd/VADODMDDCPGFinal508.pdf. Last accessed June 24, 2025.) Strength of Recommendation : Weak for
TRANSCRANIAL DIRECT- CURRENT STIMULATION
A sham-controlled trial randomized patients with MDD to escitalopram (20 mg/day) or prefrontal transcranial direct- current stimulation for 10 weeks. With mean decrease in HAM-D score from baseline, both treatment groups were superior to placebo, but transcranial direct-current stimulation was inferior to escitalopram. New-onset manic switch during transcranial direct-current stimulation therapy is a concerning adverse event; however, the number of reported cases is low [22; 45; 46].
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