1. Danish Pain Research Center, Department of Clinical Medicine, Aarhus University Hospital , Palle Juul-Jensens Boulevard 165, DK-8200 , Aarhus , Denmark
2. Department of Paediatrics and Adolescent Medicine, Aarhus University Hospital , Aarhus , Denmark
3. Department of Neurology, Aarhus University Hospital , Aarhus , Denmark
4. Department of Rehabilitation Medicine, University of Washington , Seattle , USA