1. Danish Headache Center, Glostrup, Denmark
2. Department of Neurology and National Neuromuscular Centre Norway, University Hospital of North Norway, Tromsø, Norway
3. Department of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, Norway
4. Department of General Practice, Institute of Health and Society, University of Oslo, Oslo, Norway
5. Department of Neurology, Akershus University Hospital, Lørenskog, Norway