‘Magneto’ against migraine – how transcranial magnetic stimulation works to treat migraine
By: Dr Joseph Lloyd, Headache Research laboratory, King’s College London, and Headache Centre, Guy’s and St Thomas’ NHS Foundation Trust
Dr Joseph Lloyd, who has just completed his The Migraine Trust PhD Studentship, writes about the research he undertook for his PhD
Using magnets to treat migraines? It all sounds a bit sci-fi doesn’t it?
Well, single pulse transcranial magnetic stimulation (sTMS), is clever sci-fi that only migraine patients have the privilege to use. A portable device that can be carried around and used to both treat the headache as the attacks are happening and in reducing the number of migraine days per month as a preventive treatment.
Although we know that sTMS works, it is still unclear how exactly it works to reduce migraine days in patients, and how well it’s working in a real-world, non-company sponsored NHS setting.
For the past four years, through my The Migraine Trust funded PhD, I have been investigating sTMS mechanisms of action in the Headache Research laboratory at King’s College London, and its efficacy in migraine patients prescribed sTMS at the Headache Centre at Guy’s and St Thomas’ NHS Foundation Trust, where we have been able to show how effective sTMS treatment is in reducing migraine days in a real-world population of difficult to treat patients.
sTMS fires a short magnetic pulse, which passes unimpaired through the skull and scalp, generating a small electrical current in the cortex (the superficial layers of the brain). This current locally modulates the activity of the electrically active cells (neurones) of the nervous system, which in turn control the pain signals in the brain.
What we found
Given that sTMS creates an electrical current within the cortex, that seemed the obvious place to start my research on its mechanism of action. We were able to show that sTMS reduces how active neurons are, both spontaneously and when excited. We believe this is because sTMS recruits inhibitory neurons that suppress the rest of the activity in the cortex.
The current generated by the sTMS pulse is very localised to the cortex and doesn’t spread far from the site applied. We wanted to see if, by directly effecting the neuronal activity in the cortex, sTMS can indirectly affect cortically connected structures that are involved either in the generation of a migraine attack or in sustaining the head pain?
We investigated the indirect effects of sTMS on the thalamus, a structure deep in the brain that is heavily connected to the cortex and important in the head pain pathway. What we saw was that sTMS application caused a decrease in spontaneous and induced neuronal activity, suggesting that in addition to there being less input from the cortex there is also active inhibition in the transmission of pain signals.
What this means for sTMS as a migraine treatment
These experiments showed that pain related activity in the cortex and thalamus was reduced minutes after sTMS application. Are these effects cumulative when sTMS is applied over long periods, like when patients use it as a preventive treatment? After 30 days of application in our laboratory, we found the same decrease in cortical and thalamic activity.
These outcomes suggest that sTMS’ actions persist beyond the immediate application and are cumulative the longer it is used. While there is still much work required to fully understand the exact mechanisms, this research has advanced our understanding of how sTMS works on the brain to treat migraine.
Clinically, analysis of patients’ diaries who have been prescribed the sTMS treatment at the Headache Centre at Guy’s and St Thomas’ NHS Foundation Trust, showed that this is a very safe treatment and over 50% of patients benefit from it and choose to continue using it. Importantly, sTMS had a significant impact in proving patient’s quality of life.
As a final note, I just wanted to say how much I’ve enjoyed working on this project for the last four years, I hope to be able to continue to investigate migraine mechanisms in the future and would like to thank tremendously The Migraine Trust for their support and funding.