[1] Copenhagen Univ Hosp, Rigshosp, Danish Headache Ctr, Dept Neurol, Copenhagen, Denmark
[2] Bispebjerg & Frederiksberg Copenhagen Univ Hosp, Dept Dermatol, Copenhagen, Denmark
[3] Copenhagen Univ Hosp, Rigshosp, Dept Brain & Spinal Cord Injury, Copenhagen, Denmark
[4] Univ Copenhagen, Dept Clin Med, Copenhagen, Denmark
[5] Beth Israel Deaconess Med Ctr, Dept Anesthesia Crit Care & Pain Med, Boston, MA USA
[6] Harvard Med Sch, Boston, MA USA
[7] Copenhagen Univ Hosp, Rigshosp, Dept Biochem, Glostrup, Denmark
[8] Copenhagen Univ Hosp, Rigshosp, Danish Headache Ctr, Dept Neurol, Valdemar Hansens Vej 5, DK-2600 Glostrup, Denmark