[1] Univ Aarhus, Dept Clin Epidemiol, Inst Clin, Aarhus, Denmark
[2] Univ Copenhagen, Rigshosp, Danish Multiple Sclerosis Registry, Sect 7801 Blegdamsvej 9, DK-2100 Copenhagen, Denmark
[3] Univ Southern Denmark, Natl Inst Publ Hlth, Copenhagen, Denmark
[4] Univ Southern Denmark, Inst Reg Hlth Res, Odense, Denmark
[5] Univ Copenhagen, Dept Neurol, Danish Multiple Sclerosis Ctr, Rigshosp, Copenhagen, Denmark