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Sacco S, Lampl C, Maassen van den Brink A, Caponnetto V, Braschinsky M, Ducros A, Little P, Pozo-Rosich P, Reuter U, Ruiz de la Torre E, Sanchez Del Rio M, Sinclair AJ, Martelletti P, Katsarava Z; Burden and Attitude to Resistant and Refractory (BARR) Study Group.Sacco S, et al.J Headache Pain. 2021 May 18;22(1):39. doi: 10.1186/s10194-021-01252-4.J Headache Pain. 2021.PMID: 34006218Free PMC article.