1. Headache Research Unit, Department of Neurology, University of Liège, Liège, Belgium
2. Danish Headache Centre, Department of Neurology, Glostrup Hospital, University of Copenhagen, Copenhagen, Denmark
3. Headache Group, Institute of Neurology, London, UK
4. Department of Neurology, University of Hamburg, Hamburg, Germany
5. Department of Neurology, Hospital Ruber Internacional, Madrid, Spain
6. Headache and Pain Unit, Department of Neurology, University Hospital, Zürich, Switzerland
7. University Centre for Adaptive Disorders and Headache, IRCCS C. Mondino Institute of Neurology Foundation, University of Pavia, Pavia, Italy
8. Department of Neurology, Leiden University Medical Centre, Leiden, the Netherlands