Transcranial magnetic stimulation

Transcranial magnetic stimulation
Transcranial magnetic stimulation (schematic diagram)
Specialty	Psychiatry, neurology
MeSH	D050781
[edit on Wikidata]

Transcranial magnetic stimulation (TMS) is a noninvasive form of

TMS has shown diagnostic and therapeutic potential in the central nervous system with a wide variety of disease states in neurology and mental health, with research still evolving.^{[3][4][5][6][7][8][9][10][11]}

Adverse effects of TMS appear rare and include

TMS does not require surgery or electrode implantation.

Its use can be diagnostic and/or therapeutic. Effects vary based on frequency and intensity of the magnetic pulses as well as the length of treatment, which dictates the total number of pulses given.^[14] TMS treatments are approved by the FDA in the US and by NICE in the UK for the treatment of depression and are predominantly provided by private clinics. TMS stimulates cortical tissue without the pain sensations produced in transcranial electrical stimulation.^[15]

Diagnosis

TMS can be used clinically to measure activity and function of specific brain circuits in humans, most commonly with single or paired magnetic pulses.

Treatment

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Repetitive high frequency TMS (rTMS) has been investigated as a possible treatment option with various degrees of success in conditions including[19]^[20]

• Chronic neuropathic pain
• Motor diseases (e.g., Parkinson's disease, essential tremor)
• Amyotrophic lateral sclerosis
• Multiple sclerosis
• Epilepsy
• Disorders of consciousness (e.g., vegetative state or minimally conscious state)
• Alzheimer’s disease
• Psychiatric diseases, such as depression, obsessive compulsive disorder, schizophrenia, anxiety and Tourette syndrome

Adverse effects

Although TMS is generally regarded as safe, risks are increased for therapeutic rTMS compared to single or paired diagnostic TMS.^[21] Adverse effects generally increase with higher frequency stimulation.^[12]

The greatest immediate risk from TMS is

During the procedure, a magnetic coil is positioned at the head of the person receiving the treatment using anatomical landmarks on the skull, in particular the inion and nasion.^[13] The coil is then connected to a pulse generator, or stimulator, that delivers electric current to the coil.^[2]

Physics

TMS uses

The magnetic field is about the same strength as magnetic resonance imaging (MRI), and the pulse generally reaches no more than 5 centimeters into the brain unless using a modified coil and technique for deeper stimulation.^[25]

Transcranial magnetic stimulation is achieved by quickly discharging current from a large

TMS usually stimulates to a depth from 2 to 4 cm below the surface, depending on the coil and intensity used. Consequently, only superficial brain areas can be affected.

The effects of TMS can be divided based on frequency, duration and intensity (amplitude) of stimulation:[30]

• Single or paired pulse TMS causes neurons in the neocortex under the site of stimulation to
  occipital cortex, 'phosphenes' (flashes of light) might be perceived by the subject. In most other areas of the cortex, there is no conscious effect, but behaviour may be altered (e.g., slower reaction time on a cognitive task), or changes in brain activity may be detected using diagnostic equipment.^[31]
• Repetitive TMS produces longer-lasting effects which persist past the period of stimulation. rTMS can increase or decrease the excitability of the corticospinal tract depending on the intensity of stimulation, coil orientation, and frequency. Low frequency rTMS with a stimulus frequency less than 1 Hz is believed to inhibit cortical firing while a stimulus frequency greater than 1 Hz, or high frequency, is believed to provoke it.^[32] Though its mechanism is not clear, it has been suggested as being due to a change in synaptic efficacy related to long-term potentiation (LTP) and long-term depression like plasticity (LTD-like plasticity).^[33][34]

Coil types

Most devices use a coil shaped like a figure-eight to deliver a shallow magnetic field that affects more superficial neurons in the brain.^[9] Differences in magnetic coil design are considered when comparing results, with important elements including the type of material, geometry and specific characteristics of the associated magnetic pulse.

The core material may be either a magnetically inert substrate ('air core'), or a solid,

A number of different types of coils exist, each of which produce different magnetic fields. The round coil is the original used in TMS. Later, the figure-eight (butterfly) coil was developed to provide a more focal pattern of activation in the brain, and the four-leaf coil for focal stimulation of peripheral nerves. The double-cone coil conforms more to the shape of the head.[36] The Hesed (H-core), circular crown and double cone coils allow more widespread activation and a deeper magnetic penetration. They are supposed to impact deeper areas in the motor cortex and cerebellum controlling the legs and pelvic floor, for example, though the increased depth comes at the cost of a less focused magnetic pulse.^[12]

History

In 1980 Merton and Morton successfully used transcranial electrical stimulation (TES) to stimulate the motor cortex. However, this process was very uncomfortable, and subsequently Anthony T. Barker began to search for an alternative to TES.[39] He began exploring the use of magnetic fields to alter electrical signaling within the brain, and the first stable TMS devices were developed in 1985.^[37][38] They were originally intended as diagnostic and research devices, with evaluation of their therapeutic potential being a later development.^[37][38] The United States' FDA first approved TMS devices in October 2008.^[37]

Research

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TMS has shown potential therapeutic effect on

With Parkinson's disease, early results suggest that low frequency stimulation may have an effect on medication associated dyskinesia, and that high frequency stimulation improves motor function.^[46][47] The most effective treatment protocols appear to involve high frequency stimulation of the motor cortex, particularly on the dominant side,^[48] but with more variable results for treatment of the dorsolateral prefrontal cortex.^[49] It is less effective than electroconvulsive therapy for motor symptoms, though both appear to have utility.^[50][51][52] Cerebellar stimulation has also shown potential for the treatment of levodopa associated dyskinesia.^[53]

In

TMS can also be used to map functional connectivity between the cerebellum and other areas of the brain.[61]

A study on alternative Alzheimer's treatments at the Wahrendorff Clinic in Germany in 2021^[62] reported that 84% of participants in the study have experienced positive effects after using the treatment.

Under the supervision of Professor Marc Ziegenbein, a psychiatry and psychotherapy specialist, the study of 77 subjects with mild to moderate Alzheimer's disease received frequent transcranial magnetic stimulation applications and observed over a period of time.

Improvements were mainly found in the areas of orientation in the environment, concentration, general well-being and satisfaction.

Study blinding

Mimicking the physical discomfort of TMS with

TMS research in animal studies is limited due to its early US Food and Drug Administration approval for treatment-resistant depression, limiting development of animal specific magnetic coils.^[68]

Treatments for the general public

Regulatory approvals

Neurosurgery planning

Nexstim obtained United States Federal Food, Drug, and Cosmetic Act§Section 510(k) clearance for the assessment of the primary motor cortex for pre-procedural planning in December 2009^[69] and for neurosurgical planning in June 2011.^[70]

Depression

The National Institutes of Health estimates depression medications work for 60 percent to 70 percent of people who take them.^[71][72] TMS is approved as a Class II medical device under the "de novo pathway".^[73][74] In addition, the World Health Organization reports that the number of people living with depression has increased nearly 20 percent since 2005.^[75] In a 2012 study, TMS was found to improve depression significantly in 58 percent of patients and provide complete remission of symptoms in 37 percent of patients.^[76] In 2002, Cochrane Library reviewed randomized controlled trials using TMS to treat depression. The review did not find a difference between rTMS and sham TMS, except for a period 2 weeks after treatment.^[77] In 2018, Cochrane Library stated a plan to contact authors about updating the review of rTMS for depression.^[78]

Obsessive–compulsive disorder (OCD)

In August 2018, the US Food and Drug Administration (US FDA) authorized the use of TMS developed by the Israeli company Brainsway in the treatment of obsessive–compulsive disorder (OCD).^[79]

In 2020, US FDA authorized the use of TMS developed by the U.S. company MagVenture Inc. in the treatment of OCD.^[80]

In 2023, US FDA authorized the use of TMS developed by the U.S. company Neuronetics Inc. in the treatment of OCD.^[81]

Other neurological areas

In the European Economic Area, various versions of Deep TMS H-coils have CE marking for Alzheimer's disease,^[82]

Coverage by health services and insurers

United Kingdom

The United Kingdom's

NICE evaluated TMS for severe depression (IPG 242) in 2007, and subsequently considered TMS for reassessment in January 2011 but did not change its evaluation.[89] The Institute found that TMS is safe, but there is insufficient evidence for its efficacy.^[89]

In January 2014, NICE reported the results of an evaluation of TMS for treating and preventing migraine (IPG 477). NICE found that short-term TMS is safe but there is insufficient evidence to evaluate safety for long-term and frequent uses. It found that evidence on the efficacy of TMS for the treatment of migraine is limited in quantity, that evidence for the prevention of migraine is limited in both quality and quantity.^[90]

Subsequently, in 2015, NICE approved the use of TMS for the treatment of depression in the UK and IPG542 replaced IPG242.^[91] NICE said "The evidence on repetitive transcranial magnetic stimulation for depression shows no major safety concerns. The evidence on its efficacy in the short-term is adequate, although the clinical response is variable. Repetitive transcranial magnetic stimulation for depression may be used with normal arrangements for clinical governance and audit."

United States: commercial health insurance

In 2013, several commercial health insurance plans in the United States, including

Policies for Medicare coverage vary among local jurisdictions within the Medicare system,[100] and Medicare coverage for TMS has varied among jurisdictions and with time. For example:

• In early 2012 in New England, Medicare covered TMS for the first time in the United States.^{[101][102][103][104]} However, that jurisdiction later decided to end coverage after October, 2013.^[105]
• In August 2012, the jurisdiction covering Arkansas, Louisiana, Mississippi, Colorado, Texas, Oklahoma, and New Mexico determined that there was insufficient evidence to cover the treatment,^[106] but the same jurisdiction subsequently determined that Medicare would cover TMS for the treatment of depression after December 2013.^[107]
• Subsequently,^[when?] some other Medicare jurisdictions added Medicare coverage for depression.^{[citation needed]}

See also

References