What Is rTMS?

TMS stands for Transcranial Magnetic Stimulation. It is an electromagnetic induction therapy that uses magnetic fields for stimulating nerves in the brain. The principle behind this therapy is that when a magnetic field passes through a coil, an electrical current will be produced in the coil, which can stimulate nerves in your brain or other organs in your body. This therapy has been used to treat depression and other mental disorders since 2005. Each treatment session lasts 30 minutes and consists of 30 pulses per second at a 1 Hz frequency (so 30 pulses per second).

rTMS is an acronym for Repetitive Transcranial Magnetic Stimulation, which refers to applying recurring TMS pulses to a specific brain region. rTMS has been studied as a potential treatment for several psychiatric and neurological disorders. It's also used to help study the brain. More importantly, rTMS can be used to treat depression, obsessive-compulsive disorder (OCD), and other mental health conditions.

The neuromodulatory effects depend upon several stimulation parameters such as frequency, intensity, duration, cortical target, number of sessions, and patient factors such as age, disease state, medication trial, and individual symptoms. Broadly, rTMS(repetitive transcranial magnetic stimulation) has been classified as high frequency(>1 Hz), which increases the cortical excitability, and low frequency(<1 Hz), which depresses the cortical excitability.^[1]

Goldsworthy, M. R., Hordacre, B., Rothwell, J. C., & Ridding, M. C. (2021). Effects of rTMS on the brain: is there value in variability? Cortex, 139, 43–59.

How does rTMS work?

How rTMS work

rTMS(repetitive transcranial magnetic stimulation) influences electrical brain activity through a pulsed magnetic field. This magnetic field is created by passing quick current pulses through a coil of wire. The coil of wire is encased in plastic and placed close to a client’s scalp in order for the magnetic field to be focused on particular areas of the brain. The magnetic field can safely penetrate the scalp and scull without pain, to create a current in targeted brain cells. Because this stimulation is given at regular intervals it is referred to as repetitive TMS, or rTMS.

This is a noninvasive procedure that usually takes between 30 and 60 minutesTrusted Source to perform.

What you can expect at a typical rTMS treatment session

• ?Before the treatment starts, you will need to remove anything that would be sensitive to a magnet, such as metal jewelry and credit cards. You must wear earplugs to protect your hearing, as rTMS makes a loud clicking noise. For each session of repetitive transcranial magnetic stimulation, you will sit in a comfortable reclining chair.

• The first session takes about an hour. The doctor or tech will take measurements to find the best place to put the electromagnetic coil that will deliver the magnetic pulses. They will position the electromagnetic coil so that it is resting against your head.

• To find the right dose (magnetic strength) for your treatment, the doctor will first target the motor cortex. This is the part of the brain that controls muscle movement. They will administer a few brief magnetic pulses until they find the strength that makes your hand or fingers twitch. This is known as your motor threshold.

• The doctor will then move the electromagnetic coil forward to target a different part of the brain called the dorsolateral prefrontal cortex. This area of the brain is known to be involved in depression. The measurements and the test to find your motor threshold don’t have to be repeated at every appointment.^[2]

Indications of rTMS

The therapeutic potentials for rTMS have been demonstrated for the following^[1]:

• Treatment-resistant depression
• Obsessive-compulsive disorder
• Posttraumatic stress disorder
• Tourette disorder
• Chronic pain syndrome
• Generalized anxiety disorder (GAD) 
• Bipolar disorder
• Movement disorders such as Parkinson disease, functional tremors, focal epilepsy, cortical myoclonus, spasticity.

Technical comparison of the other two protocols with rTMS

Transcranial magnetic stimulation is a unique stimulation protocol that has been used for both diagnostic and therapeutic purposes. It can be administered using three protocols: 

• Single-pulse TMS (spTMS), where the motor cortex is stimulated, and muscle activation in the contralateral limb is monitored using electromyography. Single-pulse TMS along with electromyography is helpful for presurgical planning by corticospinal tract mapping.

• Paired-pulse TMS (ppTMS) is largely delivered over the motor cortex and is used to measure cortical excitation: inhibition ratio. Two pulses are delivered consecutively at a fixed interstimulus interval and reveal the regional inhibitory or excitatory signaling strength.

• Repetitive  TMS (rTMS) is delivered in trains lasting a couple of minutes and is used commonly to suppress neuropsychiatric symptoms. For pharmacoresistant depression and PTSD, a frequency of 10 to 20 Hz is used daily for 4 to 6 weeks at the LDPFC region. Magnetic pulses are delivered for 5 to 10 seconds and turned off for another 30 to 60 seconds due to the risk of seizures and to prevent overheating.^[6]

Contraindications of rTMS

Although rTMS is a non-invasive technique and its side effect profile is rare, but it may induce seizures. Hence, it is not recommended for patients with epilepsy. Pre-existing neurological disease, adolescents, change in medication regime, substance use during the rTMS course (especially during HF-rTMS)should also be taken into account as they dlower the seizure threshold. It is, therefore, necessary that services, where rTMS is being provided, should be well equipped to deal with any seizure episode in patients.^[4]

repetitive transcranial magnetic stimulation) is relatively a well tolerable treatment but may present with pain at the stimulation site, posttreatment headaches, neck pain, or toothache. Muscle twitching during treatment can also occur. Transient changes in the auditory threshold, hyperacusis, have been demonstrated due to the loud clicks produced during TMS pulse. Hence, hearing protection is mandatory. Metallic/electronic implants or cochlear implants that are in close contact with the TMS coil serve as an absolute contraindication.^[4][5]

References:

[1] Mann SK, Malhi NK. Repetitive Transcranial Magnetic Stimulation. [Updated 2022 Mar 9]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK568715/
[2] Medically Reviewed by Dan Brennan,?MD?on June 29, 2021. Available from: https://www.webmd.com/depression/repetitive-transcranial-magnetic-stimulation
[3] Medically reviewed by Timothy J. Legg, PhD, PsyD — By Rachel Nall, MSN, CRNA — Updated on June 30, 2020. Available from: https://www.healthline.com/health/depression/repetitive-transcranial-magnetic-stimulation#uses
[4] Lefaucheur JP. Transcranial magnetic stimulation. Handb Clin Neurol. 2019;160:559-580.
[5] Taylor R, Galvez V, Loo C. Transcranial magnetic stimulation (TMS) safety: a practical guide for psychiatrists. Australas Psychiatry. 2018 Apr;26(2):189-192.
[6] Damar U, Lee Kaye H, Smith NA, Pennell PB, Rotenberg A. Safety and Tolerability of Repetitive Transcranial Magnetic Stimulation During Pregnancy: A Case Report and Literature Review. J Clin Neurophysiol. 2020 Mar;37(2):164-169.
[7] Goldsworthy, M. R., Hordacre, B., Rothwell, J. C., & Ridding, M. C. (2021). Effects of rTMS on the brain: is there value in variability? Cortex, 139, 43–59.