Transcranial Magnetic Stimulation For Depression

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Transcranial magnetic stimulation (TMS) is a non-invasive method that employs a magnetic field to modulate brain activity. It can treat depression, obsessive-compulsive disorder and other brain-related conditions in patients who have not benefited from other approaches.

Overview

Transcranial magnetic stimulation (TMS) is a method that utilises magnetic fields to stimulate nerve cells in the brain to relieve symptoms of major depression. It is a non-invasive procedure of brain stimulation because it does not involve surgery or cutting the skin. 

TMS works by applying powerful magnetic fields to specific brain regions, known to be involved in depression. An insulated coil placed over the scalp generates brief magnetic pulses, which pass easily and without pain through the skull into the brain. The pulses produced are similar in type and strength to those produced by magnetic resonance imaging (MRI) machines. 

TMS is generally well-tolerated and typically does not require anaesthesia, in contrast to alternative therapies such as electroconvulsive therapy (ECT) or medication, which often present with more noticeable side effects. 

It is also approved by the FDA (Food and Drug Administration) and is usually used as an alternative when other methods for depression have not proven successful. TMS has also been approved by the FDA to treat obsessive-compulsive disorder (OCD), migraines and to help people stop smoking when standard treatments have been ineffective.1 

Research is currently investigating additional potential applications of TMS, including the treatment of epilepsy. When used to treat depression, OCD, and to stop smoking, this approach entails sending repeated magnetic pulses, hence it is termed repetitive TMS (rTMS).

TMS in depression

Major depressive disorder (MDD) is a widespread mental health condition affecting over 300 million people globally. It leads to disability and adds to the overall burden of disease. MDD is associated with higher mortality rates, primarily due to suicide. Each year, over 700,000 people die by suicide, and many more attempt it.

Helping people effectively cope with depression is a key focus of public health. Primary treatment options for MDD include medications and psychotherapeutic approaches such as cognitive behavioural therapy. However, often patients do not respond well to these treatment options, with roughly 20–30% of patients still having severe depressive symptoms despite trying different medications and therapy. 

Moreover, resistance to antidepressants in the past lowers the chances of responding well to future medication. Because of these challenges, neuromodulation techniques such asECT and TMS are available as secondary treatments when standard treatments for depression do not work.2

Different types of TMS

TMS can be performed in different ways depending on the magnet strength or how the magnetic field is applied. 

  • Magnet strength: The strength of a magnet is generally measured in tesla (T). Typically, TMS magnets produce a magnetic field with a strength ranging from 1.5T to 2T, similar to the strength of an MRI scanner. However, the area covered by the magnetic field is much smaller in TMS compared to an MRI, due to the smaller size of the magnet
  • Pulse frequency: Each time the magnetic field turns on and off, it generates a pulse. The frequency, measured in hertz (Hz), indicates how many pulses occur per second. TMS may utilise low-frequency pulses at 1 Hz (equivalent to 1 pulse per second) or high-frequency pulses ranging from 5 Hz to 10 Hz (5 to 10 pulses per second). When TMS employs repetitive pulses, it is referred to as rTMS  
  • Pulse patterns: TMS can also employ different patterns of pulses for treatment. An example of this is the paired pulse TMS. Paired pulse TMS is a technique that consists of a conditioning stimulus followed by a test stimulus with a gap of time between the two stimuli3
  • Magnetic coil type and stimulation target: Different types of coils target different structures in the brain. For example, in Deep TMS (dTMS), an H-shaped helmed coil aims at deeper brain structures compared to TMS or rTMS. Research shows that dTMS is effective in treating conditions such as OCD4

What does TMS therapy entail?

TMS treatment requires sessions held five days a week for several weeks. Depending on the clinical protocol and the clinic’s device, sessions may last between 20 to 50 minutes. The technician identifies the optimal stimulation intensity and anatomical target by “leveraging” a particular brain structure, the motor cortex

By focusing on this area, the team can pinpoint the most suitable placement for the stimulation coil relative to the patient's brain and determine the necessary intensity for effective stimulation. The data needs then to be interpreted to find the dorsolateral prefrontal cortex, which is the area known to be involved in depression. 

The brain's excitability level can be altered starting from the first session, but noticeable results may not occur until the third, fourth, fifth, or even sixth week of treatment.

Benefits and risks of TMS

What are the benefits of TMS?

  • It’s non-invasive. It does not involve surgery or anaesthesia  
  • It's safe. The most frequent side effects are headaches
  • It’s effective. The success rates of TMS depend on the condition, but research indicates that it works efficiently
  • It can be used simultaneously with other treatments, such as medications and mental health therapy

What are the side effects, risks or complications of TMS?

A rare yet serious side effect is seizures. However, having a seizure from a TMS session is extremely rare, with only 1 in 10,000 patients suffering from seizures. TMS may also not be suitable for individuals with epilepsy, a past head injury, or other serious neurologic issues. 

Other possible complications, most of which are usually mild and last no longer than a few minutes after a session include:

  • Dizziness or lightheadedness (a feeling of faintness)
  • Ache, commonly experienced in your scalp or neck
  • Temporary tinnitus (ringing in the ears)
  • Muscles tingling in the face or scalp
  • Unusually decreased tolerance to sound (hyperacusis)  

Summary

Transcranial Magnetic Stimulation (TMS) is a non-invasive procedure that employs magnetic fields to stimulate specific regions in the brain. It has become a promising therapy for various brain-related conditions, particularly treatment-resistant depression and obsessive-compulsive disorder (OCD). 

Unlike invasive treatments such as surgery, TMS involves placing a coil on the scalp to deliver magnetic pulses to specific areas of the brain associated with the targeted disorder. TMS is considered safe and well-tolerated, making it a valuable option for patients who have not found relief from traditional treatments. 

There are different types of TMS techniques, varying in factors such as magnet strength, pulse frequency, and stimulation patterns, allowing for personalised treatment approaches. While generally safe, TMS may cause minor side effects such as headaches or dizziness, with rare instances of seizures. 

Despite how effectively it works, researchers are continuing to study additional applications of TMS and refine its use in treating various neurological conditions. Overall, TMS offers a promising alternative for patients who have not found success with traditional treatments.

References

  1. Mizutani-Tiebel Y, Tik M, Chang KY, Padberg F, Soldini A, Wilkinson Z, et al. Concurrent tms-fmri: technical challenges, developments, and overview of previous studies. Front Psychiatry [Internet]. 2022 Apr 21 [cited 2024 Feb 28];13:825205. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9069063/
  2. Sonmez AI, Camsari DD, Nandakumar AL, Voort JLV, Kung S, Lewis CP, et al. Accelerated tms for depression: a systematic review and meta-analysis. Psychiatry Res [Internet]. 2019 Mar [cited 2024 Feb 27];273:770–81. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6582998/
  3. Roumengous T, Thakkar B, Peterson CL. Paired pulse transcranial magnetic stimulation in the assessment of biceps voluntary activation in individuals with tetraplegia. Frontiers in Human Neuroscience [Internet]. 2022 [cited 2024 Feb 28];16. Available from: https://www.frontiersin.org/articles/10.3389/fnhum.2022.976014
  4. Roth Y, Barnea-Ygael N, Carmi L, Storch EA, Tendler A, Zangen A. Deep transcranial magnetic stimulation for obsessive-compulsive disorder is efficacious even in patients who failed multiple medications and CBT. Psychiatry Research [Internet]. 2020 Aug 1 [cited 2024 Feb 28];290:113179. Available from: https://www.sciencedirect.com/science/article/pii/S016517812030815

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This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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