What Causes Polyarticular Juvenile Idiopathic Arthritis?
Polyarticular JIA is an autoimmune disease. This means that the body’s immune system, which normally attacks germs, mistakenly attacks the joints. This causes inflammation (swelling and irritation) in the joints and other problems.
Polyarticular JIA usually starts when kids are 1–3 years old, or 10–14 years old. It happens more often in girls than boys.
Doctors don’t know exactly why kids and teens get JIA. “Idiopathic” means “from an unknown cause.” It can run in families but often does not. It’s likely due to a combination of: