OnabotulinumtoxinA in chronic migraine: predictors of response. A prospective multicentre descriptive study.

BACKGROUND AND PURPOSE: OnabotulinumtoxinA is a treatment specifically approved for the prophylaxis of chronic migraine in adults. The aim of this study was to assess the effectiveness of OnabotulinumtoxinA in chronic migraine after 1 year of treatment in a real-life setting and to identify clinical predictors of outcome. METHODS: We designed a prospective multicentre study performed in 13 hospitals in Spain. Patients underwent a complete medical history and examination. They were treated with OnabotulinumtoxinA every 12 weeks for 1 year. Data about outcome, adverse events, abortive medication use, emergency room use and disability were collected at 3 and 12 months. RESULTS: A total of 725 subjects completed the study. At 12 months, 79.3% showed >50% reduction in number of headaches per month and 94.9% reported no adverse events. Unilaterality of pain, fewer days of disability per month and milder headache at baseline were correlated with good outcome. Duration of disease <12 months increased the chances of response to treatment with OnabotulinumtoxinA (odds ratio, 1.470; 95% confidence interval, 1.123-2.174; P = 0.045). CONCLUSIONS: This study confirmed the effectiveness of treatment with OnabotulinumtoxinA after 1 year of treatment. The chances of a good outcome may be increased by starting treatment in the first 12 months after chronic migraine diagnosis.