Day # 40: Transcranial Magnetic Stimulation (TMS)

In our last post we discussed electroconvulsive therapy (ECT). Today we will cover another interventional treatment in psychiatry called transcranial magnetic stimulation (TMS). This discussion will include mechanism of action, indications, clinical pearls, and side effects.


Today's Content Level: Intermediate, Advanced



TRANSCRANIAL MAGNETIC STIMULATION (rTMS)


Introduction

  • As mentioned in previous lessons, some patients will not respond to standard treatment with antidepressants and psychotherapy. Electroconvulsive therapy (ECT) and transcranial magnetic stimulation (TMS) are options for these patients.

  • The TMS machine works by passing weak alternating electrical current through a metal coil placed against the scalp. This produces rapidly changing magnetic fields.

  • These magnetic signals pass through the skull and induce electric currents that depolarize neurons in a specific area of the surface of the cortex and associated neural circuits.

  • Repetitive TMS (rTMS) is delivered in a series of pulses (discussed more in technique section).


Mechanism

  • The mechanism of antidepressant/anxiolytic effects of TMS is not completely understood.

  • TMS has been shown to increase monoamine (dopamine, norepinephrine, serotonin) turnover and regulate/normalize the hypothalamic pituitary axis.

  • One hypothesis is that stimulation of discrete cortical regions results in a change in the pathologic activity in remote brain regions that are involved in mood regulation but that are connected to the targeted cortical sites of the TMS. This is supported by functional imaging studies that show repetitive TMS can change activity in brain regions remote from the site of stimulation. 1


Indications

  • Major depressive disorder (MDD): received FDA approval in 2008. Indicated for patients who have failed at least one antidepressant medication. Numerous small-scale studies have demonstrated efficacy in the treatment of major depression; however, studies show less efficacy than for ECT.

  • Migraine headaches: received FDA approval in 2013. Can be used as acute treatment and prophylaxis.

  • Obsessive compulsive disorder (OCD): received FDA approval in 2018.

  • Anxiety disorders and PTSD: limited but growing evidence for the use of TMS in anxiety disorders and trauma-related disorders. 2 The placement of the electric coils and the stimulation parameters are different than the depression protocols.

  • Clinical TMS for psychiatric applications is advancing rapidly and other conditions are currently under investigation and showing promise including bipolar disorder and schizophrenia. 3, 4.


Technique

  • Generally an outpatient procedure. Patients are awake (does not require anesthesia) and seated in a recliner chair.

  • Each session lasts around 30-40 minutes.

  • Treatment typically occurs every weekday for 4 to 6 six weeks or a total of 20-30 treatments.

  • TMS can be delivered as a single pulse (stimulus) or series of pulses (train). Stimulation with a train is called repetitive TMS (rTMS) which is most commonly done.

  • Parameters include depth, frequency, intensity, train duration, inter-train interval, and number of trains per session.

  • Stimulation site: most trials for depression have stimulated the left dorsolateral prefrontal cortex, however some trials have stimulated the right dorsolateral prefrontal cortex, the dorsomedial cortex, or have tried two cortical sites.


Clinical Pearls

  • The long-term benefits of TMS, risk of relapse, and utility of maintenance TMS are still being determine. Observational studies lasting at least sign months suggestion that in patients with major depression who improve with acute repetitive TMS, relapse occurs in about 35 percent of those without maintenance treatment. 8

  • Relative contraindications of TMS -> Implanted metallic hardware, cochlear implants, and implanted electrical devices (eg, pacemakers, intracardiac lines, medication pumps), or unstable general medical disorders. Patients with epilepsy or increased risk of seizures (eg, epilepsy, intracranial mass, and vascular abnormalities) may be contraindicated, however they can be considered for low frequency rTMS only if the potential benefit outweighs the increased risk such as in depression unresponsive to multiple courses of pharmacotherapy, psychotherapy, and/or ECT.

  • Special populations

  • TMS can be beneficial for elderly patients with depression, but the intensity must be increased to bridge the increased distance between the coil and cortex in these patients (distance increased by prefrontal atrophy). 5

  • May be safe and effective for post-stroke depression. 6

  • May be safe and effective for antenatal/postpartum depression. 7

  • Use in pediatric patients is unclear.


Side Effects

  • TMS is generally safe and well-tolerated.

  • Risk of seizure: 0.1 to 0.5 % risk if safety guidelines and stimulation parameters are followed. Factors that increase the risk of seizure include patient factors and stimulation parameters such as high frequency/intensity.

  • Does not impair cognition (unlike ECT) or increase suicidal ideation/behavior.

  • Common side effects include headache, scalp pain, and transient hearing loss.

  • Headaches: Transient headaches. No migraine headaches have been reported. Headache and scalp pain typically resolve over first two weeks of treatment. Can treat with acetaminophen or ibuprofen.

  • Scalp pain: May be more pronounced at higher stimulation frequencies. Topical lidocaine may reduce scalp pain.

  • Transient hearing loss: last less than 4 hours. Caused by repeated mechanical clicks of TMS machine. Hearing loss prevented with foam earplugs during treatment.


CONCLUSION


I hope you learned something today. TMS is an exciting and expanding technology that we can offer as an alternative treatment to our patients. Hopefully this modality can become more affordable and accessible in the near future. Next lesson will be our last post in the depressive disorders theme.


Resources for this post include Kaplan and Sadock's Synopsis of Psychiatry and UpToDate and articles referenced above.



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