1. Department of Medicine, Faculty of Medicine, Universidad de Valladolid, Valladolid, Spain
2. Headache Unit, Department of Neurology, Hospital Clínico Universitario de Valladolid, Valladolid, Spain
3. Valladolid East Primary Care, Regional Health Administration, Gerencia Regional de Salud, Junta de Castilla y Leon, Valladolid, Spain
4. Headache Unit, Department of Neurology, Hospital Universitari Son Espases, Palma de Mallorca, Spain
5. Department of Neurology, Clinica Rotger Quironsalud, Palma de Mallorca, Spain
6. Headache Unit, Department of Neurology, Instituto de Investigación Sanitaria, Hospital Universitario de la Princesa, Madrid, Spain
7. Headache and Neuralgia Unit, Department of Neurology, Hospital de la Santa Creu i Sant Pau, Barcelona, Spain
8. Headache Unit, Department of Neurology, Hospital Universitario Marqués de Valdecilla, Santander, Spain
9. Headache Unit, Department of Neurology, Hospital Clínico San Carlos, Madrid, Spain