Juvenile rheumatoid arthritis (JRA), sometimes called juvenile chronic arthritis or juvenile idiopathic arthritis, is a childhood disease that causes inflamed, swollen joints that are often stiff and painful. Symptoms common to all forms of JRA include joint pain, a disturbance in the way a child walks (abnormal gait), and joint stiffness that lasts longer than 1 hour in the morning.

The cause of JRA is not well-understood. Most experts believe it is caused by a combination of factors, including an overly active immune system.

There are three types of JRA. Each type is based on the number of joints affected during the first 6 months of active disease, whether the child has other symptoms, and which parts of the body are affected:

• Pauciarticular JRA (oligoarthritis) is the most common type of JRA. In this type, 1 to 4 joints are affected.
• Polyarticular JRA (polyarthritis) is the second most common type. Children with this type have 5 or more joints affected.
• Systemic JRA is the least common type. It can cause whole-body symptoms, such as fever and rash.