About 70 to 80 percent of all adults with rheumatoid arthritis are positive for RF, but fewer than half of all children with rheumatoid arthritis are RF positive. Presence of RF indicates an increased chance that JRA will continue into adulthood. JRA is an autoimmune disorder, which means that the body mistakenly identifies some of its own cells and tissues as foreign. The immune system, which normally helps to fight off harmful, foreign substances such as bacteria or viruses, begins to attack healthy cells and tissues. The result is inflammation-marked by redness, heat, pain, and swelling.
Scientists suspect that it is a two-step process.
The most common symptom of all types of JRA is persistent joint swelling, pain, and stiffness that typically is worse in the morning or after a nap. The pain may limit movement of the affected joint although many children, especially younger ones, will not complain of pain. JRA commonly affects the knees and joints in the hands and feet. One of the earliest signs of JRA may be limping in the morning because of an affected knee. Besides joint symptoms, children with systemic JRA have a high fever and a light pink rash.