Treatment of Chronic Migraine With Erenumab Alone or as an Add on Therapy

The investigators treated chronic migraineurs that have failed more than 3 preventive drugs with Erenumab alone or as an add on therapy to: Reduce the frequency of monthly migraine days, to evaluate If the add on of Erenumab to another preventive therapy is superior to Erenumab alone, and assess all adverse events related to the use of Erenumab. Migraineurs with 15-30 migraie days per month at baseline were clustered in 3 categories. Failure of Erenumab was defined as no improvement in the frequency of monthly migraine days. Group I: no preventive therapy, prior to the start of Erenumab. (No botox cohort). Group II: on Botulinum Toxin A (Botox), prior to the add on therapy with Erenumab. (Botox cohort).Group III: on an oral preventive drug, prior to the add on therapy with Erenumab. (No Botox cohort)