This article will review Transcranial Magnetic Stimulation as one of the treatment modalities of migraine and explore the advantages and disadvantages of it. The future of TMS therapy as a supplement to the treatment of migraine is bright.
WHAT IS MIGRAINE?
“Migraine typically presents with recurrent throbbing pain, usually unilateral and the attacks are often accompanied by nausea, vomiting, sensitivity to light and sound, and visual disturbances."
Migraine refers to a headache of differing intensity, often with associated symptoms and preceded by warning signs. Several triggers have been identified, with them varying widely from patient to patient.
It typically presents with recurrent throbbing pain, usually unilateral (bilateral in 20% patients). Attacks are often accompanied by nausea, vomiting, sensitivity to light and sound, visual disturbances, or tingling and numbness. Moreover, attacks may be preceded by mood changes, neck stiffness, aura, or constipation. Chronic daily migraines are headaches that occur for 15 days or more per month for three or more consecutive months.
Migraine is currently the 6th most disabling illness globally, with more than 4 million people worldwide having chronic daily migraine.  It affects women more than men; with the prevalence being 15% and 6% respectively.  The prevalence is also highest between ages 25-55, hence directly affecting productivity.  In the United Kingdom alone, there was a reported loss of 230,000 DALYs due to migraine. 
"Currently, over 90% of patients are using over-the-counter drugs for migraine."
Although migraine is so common, it goes unreported and under-diagnosed often. In Canada alone, 20% of people with recurrent headaches had never sought medical help.  Currently, over 90% of patients are using over-the-counter drugs for migraine.  This, in turn, leads to episodic migraine turning chronic, along with patients becoming more and more dependent on medication. Hence, newer and more innovative solutions are required for prophylaxis and effective treatment of migraine.
What is Transcranial Magnetic Stimulation?
"It is a non-invasive procedure used to induce electric current at a specific area of the brain."
Transcranial Magnetic Stimulation (TMS) is a non-invasive procedure in which a changing magnetic field is used to induce electric current at a specific area of the brain. It is currently being explored in the treatment of migraine and depression, among others. For treatment of migraine, the device is positioned on the occiput when an acute attack occurs (as early as possible), after which the magnetic pulse is delivered on pushing a button. It as a safe and painless procedure. TMS delivers magnetic pulses one at a time in single-pulse (sTMS), as a train of pulses in repetitive TMS (rTMS), or as a double-pulse in paired-pulse TMS (ppTMS). While sTMS has been primary used for acute migraine attacks (especially in those with aura), rTMS is being used as prevention therapy.
How does Transcranial Magnetic Stimulation work?
Although the exact pathophysiology of migraine is unknown, several ideas on the workings of migraine have been hypothesized. One of the more popular ones is brain hyper-excitability, which has a strong genetic basis- characterised by an increase in glutamate (excitatory neurotransmitter)  and a hyperexcitable visual cortex.  Moreover, aura has been infered to be caused due to a wave of excitability followed by cortical spreading depression (CSD).  Recent evidence shows that CSD may be one of the causative factors for activation of trigeminovascular phenomenon, which causes pain during a migraine attack.  Hence, sTMS, by inhibiting CSD, allows for pain relief as well as treatment of an acute attack of migraine.
rTMS, on the other hand, causes changes in brain excitability and a reported change in glutamate levels in the brain.  However, more extensive research is required to determine the exact pathophysiology and extent of usefulness of rTMS in prophylactic treatment of migraine.
Research on single-pulse TMS
"Studies report that 50% or more responders feel significant pain relief with sTMS."
The efficacy of sTMS (single-pulse Transcranial Magnetic Stimulation) to treat and prevent acute migraine has been reported by many studies, with a decease in associated symptoms such as nausea and vomiting, photophobia, and phonophobia. [11-13] While one study reported that 62% responders felt significant pain relief,  another reported that 50% felt the same.  Studies reported any serious side effects. However, mild adverse effects such as tingling and dizziness have been noted. Earlier, patients undergoing sTMS treatment were required to go to the clinic to get treatment. However, portable sTMS machines are now available, hence greatly improving patient compliance. A disadvantage to studies on sTMS in migraine is the sample size, with the participants usually ranging from 100-500. Hence, exploration into sTMS in migraine with a larger sample size would be optimal.
Research on repetitive TMS
"The major drawback of rTMS also lies in the research itself, with extensive research required to further our knowledge."
rTMS (repetitive Transcranial Magnetic Stimulation) has also been researched in the treatment and prophylaxis of migraine. The results, however, are variable. Some studies show statistically significant success in prevention of attacks, [14-15] with one study showing up to 98% patients noting a reduction in frequency. On the other hand, some studies did not show a significant decrease in migraine attacks. However, none of the studies reported any serious adverse events. Minor side effects, such as dizziness, tinnitus, unilateral lacrimation were noted, especially with chronic or repetitive rTMS treatment. Seizures have also been reported, though very rarely. The major drawback of rTMS also lies in the research itself, with extensive research required to further our knowledge on the mechanism and exact efficacy of this approach.
Another major disadvantage of TMS currently is the accessibility. TMS can cost between 100-200 USD for unlimited use. Hopefully, however, with the advent of newer and finer TMS technology, it will become both cheaper and more accessible, as has happened with several previous devices.
In conclusion, TMS has shown promising results to change the future of migraine therapy from one that is currently drug-based, to a more modern, dependence-free approach. Moreover, TMS may be especially useful in refractory cases, where patients do not respond to any drugs for migraine. All in all, with more research into TMS, we stand to benefit a huge amount not only in overall productivity of patients and patient compliance, but also in overall medicinal costs, as lifetime drug therapy costs more on average than TMS does. The future of TMS therapy as a supplement to the treatment of migraine is bright.
Author: Ms. Vibha Hegde
Editor: Dr. Rushil Dalwadi