Transcranial magnetic stimulation for treatment-resistant depression. Find out how it works, the risks involved in TMS, and whether it's effective in treating depression.

Transcranial magnetic stimulation (TMS) is an experimental technique that uses magnetic fields for gently stimulating the brain. Some in the research field look at TMS as a possible replacement for ECT (electroconvulsive therapy).

The Food and Drug Administration has not approved TMS for any psychiatric treatment at this time. Therefore TMS is only available as a research procedure for treatment-resistant depression (to treat depression when standard treatments such as antidepressants and therapy hasn't worked) and other mental illnesses such as OCD, bipolar disorder and PTSD.

TMS has been approved in Canada and Israel as a treatment of depression for patients who have not responded to medications and who might ordinarily be considered for a trial of electroconvulsive therapy (ECT).

How TMS Works

A treatment session with TMS lasts about 30-40 minutes and most protocols require at least two weeks of daily stimulation given five times per week. Some require up to 6 weeks.

Transcranial magnetic stimulation (TMS) utilizes a specialized electromagnet placed on the patient’s scalp that generates short magnetic pulses, roughly the strength of an MRI scanner’s magnetic field but much more focused. The magnetic pulses pass easily through the skull just like the MRI scanner fields do, but because they are short pulses and not a static field, they can stimulate the underlying cerebral cortex (brain). Low frequency (once per second) TMS has been shown to induce reductions in brain activation while stimulation at higher frequencies (> 5 pulses per second) has been shown to increase brain activation. It has also been shown that these changes can last for periods of time after stimulation is stopped. Technological improvements led to repetitive transcranial magnetic stimulation (rTMS), and a new coil design made it easier to target small areas of the brain. TMS was first developed in 1985, and has been studied significantly since 1995.

What Does Repetitive Transcranial Magnetic Stimulation Feel Like?

According to John McManamy at McMan's Depression and Bipolar Web, "rTMS is an outpatient procedure, but not a particularly pleasant one. Depending on the intensity of the frequency, patients can experience headaches and unwelcome noise. The most critical concern is the risk of seizure." For this reason, low frequency rTMS is preferred over high frequency. Frequencies are adjusted to an individual's "motor threshold."

Risks and Side-Effects of Transcranial Magnetic Stimulation

Transcranial magnetic stimulation is the least invasive of the brain stimulation procedures used for depression. It requires no surgery or implantation of electrodes or nerve stimulators. While it's considered generally safe, there are some risks involved. Common side-effects of rTMS include: scalp pain at the stimulation point, headaches, spasms of facial muscles, and lightheadedness. Other less frequent problems are hearing problems, seizures and inducing mania.

As TMS and rTMS are experimental procedures which haven't been around for a long time, long-term effects of exposure to the strong electromagnetic fields involved remain unknown. Some studies have shown structural changes in the brain after transcranial magnetic stimulation. The significance of these changes isn't yet known. Research also reveals that transcranial magnetic stimulation is less effective in people who have suffered severe depression for over 4 years or who are older.

Results From Transcranial Magnetic Stimulation

HTML clipboard As the example of patient comments about TMS above demonstrates, there's a wide variety of experiences from treatment with transcranial magnetic stimulation. They range from a vast improvement in depression symptoms to virtually no improvement at all. For those who do show improvement, research indicates it could last from days to weeks or months. Remember, this is an experimental depression treatment and researchers are learning more about different techniques to best use TMS. As research progresses, there's hope that the effectiveness of transcranial magnetic stimulation will improve.

Sources:

• Strafella AP, Paus T, Barrett J, Dagher A. J Neuroscience. 2001 Aug 1;21(15):RC157. Repetitive transcranial magnetic stimulation of the human prefrontal cortex induces dopamine release in the caudate nucleus.
• Fitzgerald PB, Brown TL, Marston NA, Daskalakis ZJ, De Castella A, Kulkarni J. Arch Gen Psychiatry. 2003 Oct;60(10):1002-8. Transcranial magnetic stimulation in the treatment of depression: a double-blind, placebo-controlled trial.
• Rohan M, Parow A, Stoll AL, Demopulos C, Friedman S, Dager S, Hennen J, Cohen BM, Renshaw PF. Am J Psychiatry. 2004 Jan;161(1):93-8. Low-field magnetic stimulation in bipolar depression using an MRI-based stimulator.
• Neuronics website
• McMan's Depression and Bipolar Web

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