Efficacy, safety, and predictors of response to botulinum toxin type A in refractory chronic migraine: a retrospective study.

BACKGROUND Due to its persistent and debilitating nature, refractory chronic migraine (RCM) can cause significant socioeconomic burden. This study retrospectively reviewed the efficacy and safety of botulinum toxin type A (BoNT-A) in the treatment of RCM. Predictors of treatment response were also investigated. METHODS We enrolled 94 patients in this study after reviewing the records of those patients who received BoNT-A injections ≥ 75 U in our headache clinic, and who fulfilled the criteria for RCM established by Schulman et al. The outcome variables included headache frequency, migraine disability assessment score, and adverse events recorded in headache diaries. Treatment response was defined as ≥ 30% reduction in headache frequency from baseline at 12 weeks. Potential predictors of treatment response were evaluated, including patient demographics, headache directionality, ocular-type headache, medication overuse, BoNT-A dosage, body mass index, and Beck depression inventory score. RESULTS For the 94 patients with RCM who were enrolled, their mean baseline headache frequency was 23.9 days/28 days. At 12 weeks after BoNT-A injection, the mean reduction in headache frequency was 6.5 days/28 days (p < 0.001), and the median migraine disability assessment score decreased from 60.0 to 30.0 (p < 0.001). Thirty-seven (39.4%) patients responded to treatment, and only ocular-type headache was associated with a higher response rate (ocular vs. nonocular, 54.8% vs. 31.7%; p = 0.031). The most common adverse event was lateral eyebrow elevation (19.1%), followed by neck soreness (5.3%). CONCLUSION About 40% of patients with RCM obtained ≥ 30% reduction in headache frequency at 12 weeks after BoNT-A injection, and treatment-related adverse events were transient and acceptable. Ocular-type headache may predict treatment response.