[1] Copenhagen Univ Hosp, Rigshosp, Danish Headache Ctr, Dept Neurol, Copenhagen, Denmark
[2] Univ Copenhagen, Fac Hlth & Med Sci, Dept Clin Med, Copenhagen, Denmark
[3] Copenhagen Univ Hosp, Neurosci Ctr, Dept Brain & Spinal Cord Injury, Rigshosp, Copenhagen, Denmark
[4] Beth Israel Deaconess Med Ctr, Dept Anesthesia Crit Care & Pain Med, Boston, MA USA
[5] Beth Israel Deaconess Med Ctr, Comprehens Headache Ctr, Boston, MA USA
[6] Harvard Med Sch, Cambridge, MA USA
[7] Harvard Med Sch, BIDMC Comprehens Headache Ctr, Dept Anesthesia Crit Care & Pain Med, Beth Israel Deaconess Med Ctr, 330 Brookline Ave, Boston, MA 02215 USA