Our objectives are to better understand pain involvement in children with myelitis and to develop diagnostic imaging techniques to detect different demyelinating stages of myelitis. The study takes place on-site at Boston Children’s Hospital and includes pain sensitivity testing and two MRI scans of the spinal cord, without contrast injections. Each study session takes approximately 3.5 hours. Participants will receive a $100 Visa gift card. They will also receive an additional $10 gift card each time they refer a friend who qualifies for the study as a healthy volunteer.