1. BIDMC Comprehensive Headache Center , Harvard Medical School , Boston , MA , USA
2. Department of Neurology, Critical Care and Pain Medicine , Harvard Medical School, Beth Israel Deaconess Medical Center , Boston , MA , USA
3. Department of Anesthesia, Critical Care and Pain Medicine , Harvard Medical School, Beth Israel Deaconess Medical Center , Boston , MA , USA
4. Department of Clinical Medicine, Faculty of Health Sciences , University of Copenhagen , Copenhagen , Denmark
5. Danish Headache Center, Department of Neurology, Faculty of Health Sciences , University of Copenhagen, Rigshospitalet Glostrup , Glostrup , Denmark
6. Department of Orthopedic Surgery , University of Copenhagen , Copenhagen , Denmark
7. Department of Neurology , Albert Einstein College of Medicine and Montefiore Headache Center , Bronx , NY , USA