Chronic migraine is a disabling condition defined as more than 15 headache day by month for more than 3 months, of which more than eight episodes are migraineous. The diagnosis of this disorder requires the assumption that a medication overuse headache has been excluded. However, the role of overuse medication for chronic migraine is practically impossible to ascertain as the majority of patients with chronic migraine inevitably consume high quantities of drugs for pain (as the life-egg-chicken problem). Prevalence rates of chronic migraine could be 1-5% in the general population. Furthermore, 2-5% of patients with episodic migraine (less than 15 headache days by month) could evolve to chronic migraine. Chronic migraine is a disabling condition as it causes loss of time from working and social activities. At work, these patients are less efficient and productive. Depression and anxiety are inevitably (80-100% of patients). Prophylactic drugs that are used for episodic migraine are often not efficacious for chronic migraine or have side effects. BOTOX intramuscular injection on several points the face, head and neck are the only approved pharmacological treatment for this disorder but more than 3 cycles of treatment could be necessary to obtain some results. The neurologist should also take in account to treat co-morbidities and other trigger factors (for example social factors) that are often present in patients suffering of chronic migraine
Finally, repetitive magnetic stimulation (rTMS), could be a useful neuromodulating treatment for chronic migraine when all the other treatment failed. rTMS (on the occipital visual cortex) showed already encouraging results for episodic migraine prevention and for the treatment of the migraneous aura.
rTMS is a noninvasive method used to stimulate small regions of the brain. During a rTMS procedure, a magnetic field generator, or “coil” is placed near the head of the person receiving the treatment (see the machine in my office in the picture). The coil produces small electrical currents in the region of the brain just under the coil via electromagnetic induction. The coil is connected to a pulse generator, or stimulator, that delivers electrical current to the coil. The magnetic field applies to the brain up to 3-7 cm under the skull, about 2000 times during a standard session (15-30 minutes). Thus, rTMS can induce increases or decreases in excitability of large populations in deep areas of the brain. Excitation or inhibition of thalamo-cortical circuits could reset pain neural pathways.
The treatment has almost no side effects. However, patients with epilepsy are excluded from the procedure because of the risk of crisis. Rarely the procedure could give mild local discomfort and pain. Some patients experience transitory changes in working memory and mood.
However, results of recent studies of rTMS are still preliminary and sometime negative for chronic migraine. Such studies indicate also a powerful placebo response to the sham stimulation (probably due to the suggestion to become magnetized! (“I magnetize you the doctor said”). It is not yet clear which the part of the brain to stimulate is and this could be a very important limiting factor for the procedure.
In the future, neuromodulation with rTMS will probably have a better place in chronic migraine treatment, especially because of its attractive safety profile. However, now, which protocol would you suggest for rTMS in patients with chronic migraine?
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