OnabotulinumtoxinA for chronic migraine: A real-life multicenter study of 479 patients.

Background: Chronic migraine (CM) is a neurological disorder that poses significant treatment challenges, particularly when complicated by medication-overuse headache (MOH). Objectives: This study aimed to evaluate the effectiveness of onabotulinumtoxin A (BoNT-A) in a large cohort of Polish patients within national reimbursement program and to identify clinical predictors of treatment response. Design: Retrospective observational cohort study. Methods: This was a retrospective multicenter observational study of 479 patients (88.9% female, mean age 43.6±11.6 years) treated with BoNT-A (195 U, PREEMPT protocol) across 12 tertiary headache centers. All patients had failed at least two prior oral preventive therapies. Effectiveness was assessed after three treatment cycles (9 months). Uni- and multivariable logistic regression analyses were performed to evaluate factors associated with treatment response, defined as a ≥50% reduction in monthly headache days (MHD). Results: At baseline, the mean MHD was 19.1±4.4. After 9 months, the mean reduction in MHD was 5.9±5.4 days, and the Migraine Disability Assessment Scale (MIDAS) score improved by an average of 52.7±48.3 points. At the 9-month follow-up, 27.3% of patients achieved a ≥50% reduction in MHD, and 23.2% were partial responders (25-49% reduction). Notably, 41.6% of patients with concomitant MOH at baseline no longer met the criteria for MOH after treatment. Multivariable analysis identified a positive family history of migraine (OR=0.55; 95% CI 0.36-0.84; p=0.005) and ≥4 prior preventive medication failures (OR=0.61; 95% CI 0.37-0.98; p=0.04) as independent predictors of a poorer response. However, the model demonstrated low discriminative ability (AUC=0.605; cross-validated AUC=0.54). Conclusions: BoNT-A is an effective and safe treatment for CM in a real-world setting, significantly reducing headache burden and MOH rates. While high treatment resistance and genetic predisposition were statistically associated with a poorer response, the poor predictive ability of the clinical model suggests that standard clinical phenotypes alone are insufficient to predict BoNT-A outcomes. These findings highlight the challenges of managing highly refractory populations within strict programmatic frameworks.