To assess whether there is a sustained benefit and good safety with repeated onabotulinumtoxinA sessions in chronic migraine over more than three years of treatment.

We prospectively enrolled 65 chronic migraine patients, who were classified as responders after three sessions of onabotulinumtoxin A and were eligible to further continue treatment.

Evidence on whether the therapeutic effect and good safety profile of onabotulinumtoxinA (Botox®) in chronic migraine (CM) patients is maintained over long term treatment is still limited. This study aims at assessing whether there is a sustained benefit and good safety with repeated onabotulinumtoxin A sessions in CM over more than three years of treatment.

This study prospectively enrolled 65 CM patients, who were classified as responders after three sessions of onabotulinumtoxinA and were eligible to further continue treatment. Data documenting longitudinal changes from the trimester after the third onabotulinumtoxinA administration (T1) to the trimester after completing two years of treatment (T2) and eventually to the trimester after completing three years of treatment (T3) in (i) mean number of monthly headache days (ii) migraine severity as expressed by the mean number of days with peak headache intensity of >4/10, and (iii) mean number of days with use of any acute headache medication, were prospectively collected from patients' headache diaries.

Inclusion Criteria:

• Patients diagnosed with chronic migraine according to IHC-III with or without medication overuse.
• Responders defined as patients that after 3 sessions of treatment with onabutulinum toxin A, having experienced a ≥50% reduction in their average monthly migraine days

Exclusion Criteria:

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