Mar 04 2010

Treating Migraine with Magnetic Stimulation

Since the discovery of magnetism, using magnets and magnetic fields has been a popular subject for quacks and charlatans – starting with Anton Mesmer and his “animal magnetism.” Recently there has been a resurgence of dubious magnetic devices for arthritis, pain, injuries, and other uses.

But today I am writing about the legitimate science of using magnetic stimulation for therapeutic effects. The brain is both a biochemical organ and an electromagnetic organ. Until recently our attempts at altering the physiology and function of the brain have focused on pharmacology – mainly either increasing or decreasing the action of specific neurotransmitters. This is an effective paradigm for seizures, preventing migraines, and treating pain. It has also been the approach for treating psychiatric disorders, with clear effects for psychotic symptoms, like those caused by schizophrenia, and also anxiety, eating disorders and severe depression. The effectiveness of pharmacological treatments for some psychiatric indications, however, remains marginal and controversial, for example for mild to moderate depression.

Because the brain is also an organ that interacts with the environment, there are also several specialties dedicated to addressing psychological concerns with environmental treatments – cognitive behavioral therapy, for example.

Electrical/magnetic interventions, however, have been scant, only recently getting significant attention. The only such intervention I can think of before the last decade was electroconvulsive therapy (ECT) for depression. It was observed serendipitously that some patients with severe depression and epilepsy would have relief of their depression following a seizure. This lead to the initial crude ECT treatments, inducing whole brain seizures. Later sedatives and paralytics were added for patient safety and comfort (avoiding the “One Flew Over the Cuckoo’s Nest” scene). ECT has been further revised to only induce seizures in one hemisphere, and recently using magnetic rather than electrical stimulation. While much safer and more effective, ECT is still a very crude intervention.

There are currently two electrical-based neurological treatments that are FDA approved. The first is a vagal nerve stimulator for refractory epilepsy. This uses an implanted stimulator outside the brain to stimulate through the vagal nerve and disrupt the synchronized firing of neurons that begin a seizure. This reduces, but does not eliminate, seizures in some patients and may reduce the need for multiple medications.

The second is implanted electrodes for Parkinson’s disease. These electrodes are implanted directly in the brain, in one of the structures of the basal ganglia, and produce steady stimulation to alter the action of the basal ganglia circuitry. This can be useful in decreasing tremor and rigidity in Parkinson’s disease, and again may reduce but not eliminate symptoms and reduce the need for medication.

These two interventions are interesting, but still fairly crude. We are starting to target specific brain regions with specific frequency and intensity of stimulation, but the potential remains for far greater precision and control. For example, research is underway to develop computer chips that contain embedded neurons that will hopefully be able to release inhibitory neurotransmitters directly a the time and location of the start of a seizure.

The new treatment represents yet another approach to using electromagnetism to affect brain function – the use of transcranial magnetic stimulation (TMS). TMS today is used for research – at different frequencies TMS can either induce or inhibit the activity in a focused part of the brain, and the results can be studied to figure out what that part of the brain does.

There is already published research looking at the effects of different frequencies of TMS on the excitability of brain regions during a migraine. A migraine is, in some ways, like a seizure – it is a neurological event involving abnormal activity in certain brain circuits (the trigeminovascular reflex, for example) and also involving hyperexcitability (leading to central sensitization) of certain populations of neurons. This leads clinically to hypersensitivity to sound, light, smell, and touch – which can both trigger and exacerbate a migraine.

The new study, soon to be published in Lancet Neurology, is a placebo-controlled pilot study using the frequency of TMS that prior research suggested would decrease the excitability of neurons during a migraine. The study used a hand-held device that a migraine sufferer can place at the back of the head and activate at the beginning of a migraine. The study showed a 40% pain free result at 2 hours – which is a clinically significant result, and a greater response at 2, 24, and 48 hours beyond the placebo group.

Incidentally, this treatment may be easy to blind as the patient uses what is essentially a black box. They press the button and have no way of knowing if a real TMS is being given. I have not seen the full report yet – so I don’t know if the placebo group devices gave no magnetic field and if that can be detected by users. Alternatively, the control device could give a non-therapeutic magnetic field as an active control.

This is preliminary research, and larger, more rigorous follow up studies need to be done. But it is highly plausible that this kind of treatment could provide a way for migraineurs to “turn off” their migraines by inducing inhibition through TMS in the hyperexcitable neurons that trigger and propagate a migraine. Side effects should also be minimal. We should not take safety for granted, however, and of course studies will have to follow patients to make sure there are no unintended consequences (sedation, cognitive impairment, or seizures, for example).

TMS has tremendous potential, as it does not require any implantable device – the fields can be induced from the outside. And I am encouraged that they were able to design a hand-held device capable of delivering an effective TMS pulse. Frequency, duration, intensity, and location of stimulation can all be varied in order to theoretically target different symptoms and conditions. We may be seeing the beginning of a new therapeutic paradigm in neurology.

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