Sacco, Simona; Lampl, Christian; Maassen van den Brink, Antoinette; Caponnetto, Valeria; Braschinsky, Mark; Ducros, Anne; Little, Patrick; Pozo-Rosich, Patricia; Reuter, Uwe; Ruiz de la Torre, Elena; Sanchez Del Rio, Margarita; Sinclair, Alexandra J.; Martelletti, Paolo; Katsarava, Zaza; Dubroja, Ivan; Hucika, Zlatko; Lisak, Marijana; Lovrencic-Huzjan, Arijana; Lušić, Ivo; Mahovic Lakusic, Darija: Burden and attitude to resistant and refractory migraine: a survey from the European Headache Federation with the endorsement of the European Migraine & Headache Alliance