1. Hospital Ruber International, Servicio de Neurología, Madrid, Spain
2. Universidade Federal do Rio de Janeiro, Hospital Universitário Clementino Fraga Filho, Setor de Cefaléias, Serviço de Neurologia, Rio de Janeiro, Brazil
3. Headache Centre, Department of Neurological Sciences, University of Pavia, C. Mondino Foundation, Pavia, Italy
4. Norges Teknisk Naturvitenskapelige Universitet, Det Medisinske Fakultet, Regionsykehuset i Trondheim, Nevrologisk Avdeling, Trondheim, Norway