Is Allodynia a Determinant Factor in the Effectiveness of Transcranial Direct Current Stimulation in the Prophylaxis of Migraine?

Objectives Allodynia, the clinical marker of central sensitization, affects even simple daily living activities and increases the tendency for migraine to be more resistant to treatment and have a chronic course. Migraine that impairs quality of life can often be treated with variable pharmaceutical agents, but with various side effects. Transcranial direct current stimulation (tDCS) is a potential alternative treatment for migraine prophylaxis. Materials and Methods Seventy‐seven patients diagnosed with migraine (48 with allodynia and 29 without allodynia) were included in the study. Randomly, 41 of the 77 patients received sham stimulation and 36 patients underwent three sessions of anodal left primary motor cortex stimulation for 2 mA, 20 min. Migraine attack characteristics (frequency, severity, and duration) and analgesic drug use were followed with headache diaries for one month after the stimulation. Results After tDCS, migraine attack frequency (p = 0.021), the number of headache days (p = 0.005), duration of attacks (p = 0.008), and symptomatic analgesic drug use (p = 0.007) decreased in patients receiving active tDCS, compared to the sham group. The therapeutic gain of tDCS was calculated as 44% (95% confidence interval [CI]: 22–60%) for headache days and 76% (95% CI: 55–86) for headache duration. Response to tDCS treatment was higher in patients without allodynia (60% vs. 24%; p = 0.028) and allodynia came out as an independent predictor of response to tDCS with logistic regression analysis. Side effects were rare and similar to the sham group. Conclusions tDCS is a safe, efficacious, and fast method for migraine prophylaxis. However, the administration of tDCS before allodynia occurs, that is, before central sensitization develops, will provide increased responsiveness to the treatment. Significance tDCS is more effective before the development of allodynia, but it also improves the quality of life even after the development of allodynia.