Department of Rehabilitation, Sykehuset Innlandet HF, Gjøvik, Norway The Norwegian Multiple Sclerosis Registry and Biobank, Haukeland University Hospital, Bergen, Norway Department of Neurology, Haukeland University Hospital, Bergen, Norway Department of Clinical Medicine, University of Bergen, Bergen, Norway Griesheim, Germany Department of Neurology, Molde Hospital, Molde, Norway Unit for Applied Clinical Research, Norwegian University of Science and Technology, Trondheim, Norway.