1. Danish Headache Center and Department of Neurology, Glostrup Hospital, Faculty of Health Sciences , University of Copenhagen , Glostrup, DK-2600 Copenhagen , Denmark
2. Department of Clinical Biochemistry, Bispebjerg Hospital, Faculty of Health Sciences , University of Copenhagen , Bispebjerg Bakke 23, DK-2400 Copenhagen NV , Denmark
3. Department of Anesthesiology, Glostrup Hospital, Faculty of Health Sciences , University of Copenhagen , DK-2600 Glostrup , Denmark