1. Department of Neurology (E.S.K., C.E.H., K.G.V., K.W.F.), Akershus University Hospital, Lørenskog, Norway.
2. Department of General Practice, Institute of Health and Society, University of Oslo, Norway (E.S.K.).
3. Department of Radiology (S.Z.), Akershus University Hospital, Lørenskog, Norway.
4. Danish Headache Center, Glostrup—University of Copenhagen, Denmark (J.M.H.).