Transcranial Direct Current Stimulation (tDCS) of the visual cortex: a proof-of-concept study based on interictal electrophysiological abnormalities in migraine

Background: Preventive pharmacotherapy for migraine is not satisfactory because of the low efficacy/tolerability ratio of many available drugs. Novel and more efficient preventive strategies are therefore warranted. Abnormal excitability of cortical areas appears to play a pivotal role in migraine pathophysiology. Transcranial direct current stimulation (tDCS) is a non-invasive and safe technique that is able to durably modulate the activity of the underlying cerebral cortex, and is being tested in various medical indications. The results of small open studies using tDCS in migraine prophylaxis are conflicting, possibly because the optimal stimulation settings and the brain targets were not well chosen. We have previously shown that the cerebral cortex, especially the visual cortex, is hyperresponsive in migraine patients between attacks and provided evidence from evoked potential studies that this is due to a decreased cortical preactivation level. If one accepts this concept, anodal tDCS over the visual cortex may have therapeutic potentials in migraine prevention, as it is able to increase neuronal firing. Objective: To study the effects of anodal tDCS on visual cortex activity in healthy volunteers (HV) and episodic migraine without aura patients (MoA), and its potentials for migraine prevention. Methods: We recorded pattern-reversal visual evoked potentials (VEP) before and after a 15-min session of anodal tDCS over the visual cortex in 11 HV and 13 MoA interictally. Then 10 MoA patients reporting at least 4 attacks/month subsequently participated in a therapeutic study, and received 2 similar sessions of tDCS per week for 8 weeks as migraine preventive therapy. Results: In HV as well as in MoA, anodal tDCS transiently increased habituation of the VEP N1P1 component. VEP amplitudes were not modified by tDCS. Preventive treatment with anodal tDCS turned out to be beneficial in MoA: migraine attack frequency, migraine days, attack duration and acute medication intake significantly decreased during the treatment period compared to pre-treatment baseline (all p < 0.05), and this benefit persisted on average 4.8 weeks after the end of tDCS. Conclusions: Anodal tDCS over the visual cortex is thus able to increase habituation to repetitive visual stimuli in healthy volunteers and in episodic migraineurs, who on average lack habituation interictally. Moreover, 2 weekly sessions of anodal tDCS had a significant preventive anti- migraine effect, proofing the concept that the low preactivation level of the visual cortex in migraine patients can be corrected by an activating neurostimulation. The therapeutic results indicate that a larger sham-controlled trial using the same tDCS protocol is worthwhile

Chronic Migraine: Epidemiology, Mechanisms, and Treatment

Chronic migraine is a debilitating primary headache disorder associated with high personal, familial, and social impact. The diagnosis is made when there are at least 15 headache days monthly including 8 migraine days per month for at least 3 months. The prevalence is 1.4–2.2% in the population. Among individuals diagnosed with chronic migraine, there may be significant variability in headache days with a potential to remit, remain unchanged, or progress to even greater disability. Most chronic migraine progresses from episodic migraine, with several identified risk factors for chronic migraine and migraine progression. The exact mechanism of chronic migraine is unknown but is associated with an increased cortical excitability, central sensitization, alternations in nociceptive signaling, as well as physiological, structural, and functional brain changes. There is evidence for both nonpharmacological and pharmacological treatment options to restore function. The best currently established pharmacologic evidence for the treatment of chronic migraine is onabotulinumtoxinA and topiramate. Behavioral treatments may improve headache symptoms and comorbidities. Emerging data shows potential benefit for neurostimulation, and large well-designed studies are needed. Multicenter randomized placebo-controlled studies of monoclonal antibodies to the calcitonin gene-related peptide, or its receptor, have demonstrated efficacy, tolerability, and safety. Biomarkers are needed to guide prognosis, treatment response, and clinical trials. The concept and management of refractory chronic migraine is discussed, and clinically meaningful endpoints are reviewed