1. National Institute of Public Health, Øster Farimagsgade 5, DK-1399 Copenhagen K, Denmark, The Danish Multiple Sclerosis Registry, Rigshospitalet 7013, Tagensvej 20, DK-2200 Copenhagen N, Denmark,
2. National Institute of Public Health, Øster Farimagsgade 5, DK-1399 Copenhagen K, Denmark, The Danish Multiple Sclerosis Registry, Rigshospitalet 7013, Tagensvej 20, DK-2200 Copenhagen N, Denmark
3. The Danish Multiple Sclerosis Registry, Rigshospitalet 7013, Tagensvej 20, DK-2200 Copenhagen N, Denmark, Department of Neurology, Aalborg Hospital North, DK-9100 Aalborg, Denmark
4. The Danish Multiple Sclerosis Registry, Rigshospitalet 7013, Tagensvej 20, DK-2200 Copenhagen N, Denmark, MS Clinic (Sønderborg, Vejle, Esbjerg) and Department of Neurology, Sydvang, Sønderborg Sygehus, DK-6400 Sønderborg, Denmark