[1] Univ Copenhagen, Glostrup Hosp, Danish Headache Ctr, Dept Neurol, DK-2600 Copenhagen, Denmark
[2] Univ Munster, Dept Neurol, D-4400 Munster, Germany
[3] Univ Gothenburg, Sahlgrenska Acad, Inst Neurosci & Physiol, Gothenburg, Sweden
[4] Athens Naval Hosp, Dept Neurol, Headache Clin, Athens, Greece
[5] Univ Pavia, IRCCS C Mondino Inst Neurol Fdn, Univ Ctr Adapt Disorders & Headache, I-27100 Pavia, Italy
[6] Univ Liege, Headache Res Unit, Dept Neurol, Liege, Belgium
[7] St Olavs Hosp, Norwegian Natl Headache Ctr, Trondheim, Norway
[8] Norwegian Univ Sci & Technol, Dept Neurosci, N-7034 Trondheim, Norway