European headache federation consensus on the definition of resistant and refractory migraine - Sacco, Simona (Regional Referral Headache Center of the Abruzzo region) ; Braschinsky, Mark (Tartu University Clinics) ; Ducros, Anne (University Hospital of Montpellier (França)) ; Lampl, Christian (Hospital Barmherzige Brüder) ; Little, Patrick (European Migraine & Hendrik Ido Ambacht) ; van den Brink, Antoinette Maassen (Erasmus MC University Medical Center Rotterdam) ; Pozo-Rosich, Patricia (Hospital Universitari Vall d'Hebron) ; Reuter, Uwe (Charité - Universitätsmedizin Berlin) ; de la Torre, Elena Ruiz (Hendrik Ido Ambacht) ; Del Rio, Margarita Sanchez (Clínica Universidad de Navarra) ; Sinclair, Alexandra J. (Birmingham Health Partners) ; Katsarava, Zaza (IM Sechenov First Moscow State Medical University) ; Martelletti, Paolo (Sant'Andrea Hospital) ; Universitat Autònoma de Barcelona