The problem usually develops in young adults. Signs include fever, stiff neck, hyper-reactivity to touch, and reduced mobility due to marked stiffness. It can be acute or chronic. The cause is not well understood, but because it responds to steroid therapy, it is likely an autoimmune condition. Autoimmune problems occur when the body sees itself as foreign and mounts a reaction. There is the possibility that infectious agents can trigger this reactivity. Steroid medications have anti-inflammatory action, and at high doses, inhibit the immune system.