OnabotulinumtoxinA was approved for treatment of chronic migraine (CM) after publication of Phase 3 Research Evaluating Migraine Prophylaxis Therapy (PREEMPT) trials. However, the PREEMPT trials lasted only up to 1 year. The main aim of our retrospective study was to evaluate whether a prolonged treatment of onabotulinumtoxinA (18 months, six quarterly cycles) will sustain or further improve the efficacy results and the quality of life achieved at 6 and 12 months. Patients were adults with CM with or without overuse of drugs, with at least six regularly repeat onabotulinumtoxinA treatments, administered according to the PREEMPT protocol. The outcomes were investigated after 6, 12, and 18 months of treatment with respect to baseline and with respect to each previous study time point. Headache days and hours, and dosage of headache medication taken with latency period, were collected from the patients daily. Quality of life was evaluated by means of the Migraine Disability Assessment (MIDAS) questionnaire. At each study time point, the proportion of responder patients with respect to baseline was evaluated. For all measures, the baseline data were referred to the previous month before starting. Forty-seven patients were evaluated. Our data show a decrease in the monthly headache days and hours, at each study evaluation, with respect to the previous one. They showed that beyond the first year, a statistically significant difference in the monthly days of headache compared at 18 vs. 12 months is observed. A significantly higher proportion of patients (with a response greater than 75% decrease from baseline in the frequency of headache days and hours) was observed at month 18 compared to month 12. The proportion of patients in MIDAS grade I increased over time, and a statistically significant improvement in MIDAS I score was obtained from month 12 to month 18. A positive modification in the consumption of analgesics over time was observed (p for trend <0.001). The mean acute drug latency strongly decreased over time. Our study confirmed that onabotulinumtoxinA is an effective treatment to reduce headache-related disability and improve patients' quality of life, highlighting that upon repeated administration, the therapy efficacy increases significantly and a progressive trend of "first-time response" is observed for the entire period under consideration.
Keywords: Chronic migraine; Medication overuse headache; Migraine abuse; OnabotulinumtoxinA; Preventative therapy.