[1] Univ Copenhagen, Rigshosp Glostrup, Dept Neurol, Danish Headache Ctr, Valdemar Hansens Vej 5, DK-2600 Glostrup, Denmark
[2] Natl & Kapodistrian Univ Athens, Sch Med, Eginit Hosp, Neurol Dept 1, Athens, Greece
[3] Univ Modena & Reggio Emilia, Dept Diagnost, Med Toxicol Headache & Drug Abuse Res Ctr, Clin & Publ Hlth Med, Modena, Italy
[4] Epilepsy & Migraine Treatment Ctr, Krakow, Poland
[5] Sapienza Univ Rome Polo Pontino, Dept Medicosurg Sci & Biotechnol, Latina, Italy
[6] Guys & St Thomas NHS Trust, Headache Ctr, London, England
[7] Tartu Univ Clin, Neurol Clin, Headache Clin, Tartu, Estonia
[8] NTNU Norwegian Univ Sci & Technol, Dept Neuromed & Movement Sci, Trondheim, Norway
[9] St Olavs Univ Hosp, Norwegian Advisory Unit Headache, Trondheim, Norway