Transcranial magnetic stimulation is a promising therapy for patients suffering from treatment-resistant depression. In this Psychiatric Times article, Abhijit Ramanujam, MD, explains the benefits of this noninvasive treatment and how it works.
Repetitive transcranial magnetic stimulation (TMS) is a useful clinical tool that is effective in patients with treatment-resistant depression. This noninvasive treatment is an option for patients with depression who have not found relief from other treatments, such as psychotherapy and antidepressants.
TMS technology was developed in 1985 and has been gaining clinical interest since then. Two-thirds of TMS patients experienced either full remission of their depression symptoms or noticeable improvements.
Mechanism of action
Approved by the US Food and Drug Administration in 2008, TMS uses an alternating current passed through a metal coil placed against the scalp to generate rapidly alternating magnetic fields. These pass through the skull nearly unimpeded and induce electric currents that depolarize neurons in a focal area of the surface cortex.
High-frequency stimulation is thought to excite the targeted neurons and is typically used to activate the left prefrontal cortex. Low-frequency stimulation appears to inhibit cortical activity and is usually directed at the right prefrontal cortex.
Consistent with this hypothesis, a review examined 66 studies in depressed patients who were treated with TMS targeting the dorsolateral prefrontal cortex. It found that high-frequency TMS generally increased regional cerebral blood flow, whereas low-frequency TMS generally decreased regional cerebral blood flow, which is reduced in a depressed brain.
When conducting a patient assessment for TMS, the purpose of the evaluation is to confirm the primary diagnosis of treatment-resistant depression and determine whether the TMS intervention can be used safely. The assessment includes examinations of psychiatric history, general medical history, physical health, and mental status with emphasis upon depressive symptoms. This should emphasize risk factors for seizures and preexisting neurologic disease, such as epilepsy, intracranial masses, and vascular abnormalities.
TMS is contraindicated in patients with increased risks for seizures, implanted metallic hardware (aneurysm clips, bullet fragments, etc), cochlear implants, implanted electrical devices (pacemakers, intracardiac lines, medication pumps, etc), and unstable general medical disorders.
Multiple reviews have found consistent evidence that TMS provides a clinically relevant benefit to patients with treatment-resistant depression. In patients with acute major depression who have not responded to at least one antidepressant medication, numerous meta-analyses of randomized trials have found that TMS is superior to placebo treatment. It is not known if maintenance treatment with TMS for unipolar major depression is beneficial.
TMS is less effective than ECT; however, TMS does not require general anesthesia, and it can be done in an outpatient setting. Unlike with ECT, patients with major depression do not experience impaired cognition with TMS.
Predictors of response
No consistent predictors have been identified in meta-analyses. A 1-year, prospective observational study of 120 patients who responded or remitted with acute TMS found that the durability of response to TMS was not associated with age, sex, severity of depressive symptoms prior to TMS, nor the number of failed antidepressant trials prior to TMS.
For treatment of major depression, TMS is less efficacious than ECT. Follow-up studies of patients with major depression who were treated acutely with TMS in randomized trials indicate that the short-term benefits of TMS are stable. With regard to longer-term benefits of TMS, prospective, observational studies lasting at least months suggest that in patients with major depression who improve with acute TMS, relapse occurs in about 35%.
Safety and adverse effects
TMS is generally safe and well-tolerated. The most serious adverse effect of TMS is a generalized tonic-clonic seizure. However, the risk of seizure appears to be comparable to that for antidepressant medications.
Elderly: For elderly patients with major depression, TMS can be beneficial if the stimulation intensity is sufficient.
Poststroke depression: Depression frequently occurs after stroke, and TMS may help these patients.
Pregnancy and postpartum depression: For these patients with major depression, observational studies suggest that TMS may possibly be safe and effective. It appears unlikely that the fetus is directly affected by TMS because magnetic fields rapidly attenuate with distance.
Read the full Psychiatric Times article with sources.
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