1. Headache Research Unit, Department of Neurology, University of Liège, Liège, Belgium
2. Headache Clinic, INM Neuromed, IRCCS, Pozzilli (Isernia), Italy
3. Danish Headache Centre, Department of Neurology, Glostrup Hospital, University of Copenhagen, Copenhagen, Denmark
4. Department of Neurology, Istanbul Faculty of Medicine, Istanbul, Turkey
5. Headache Group, Institute of Neurology, Queen Square, London, UK