Diagnosing arthritis in children dates back to the mid-1800s. Today, rheumatologists and other kinds of doctors treat several types of juvenile idiopathic arthritis (JIA), each with its own symptoms. Two forms of the disease include polyarticular JIA, or PJIA, and systemic JIA, or SJIA.
The key to PJIA is the polyarticular. Let’s break it down further: poly means many. So think of polyarticular as many joints (5 or more, according to its medical definition). Juvenile simply describes the age group affected by the disease. While arthritis means inflammation of one or more joints, idiopathic refers to the cause of the disease: it’s unknown.
The immune system is complex. It has many different kinds of cells that protect the body by fighting harmful things like bacteria, fungi, and viruses. When the immune system is not working correctly, it can lead to the signs and symptoms of PJIA, such as inflammation, pain, and stiffness.
PJIA has things in common with other forms of JIA—joint pain, for example. But PJIA is unique because of that “5 or more joints” feature. Other forms of JIA typically affect a limited number of joints. In addition, a child with PJIA may find it difficult to chew food, because PJIA can affect not just smaller joints like those in fingers or toes, but also larger joints such as those in the jaw or neck. And unlike some forms of JIA, PJIA often affects both sides of the body, not just one side.
Also, PJIA does not include body-wide symptoms such as rashes or high fevers common to another form of JIA called systemic JIA (SJIA). PJIA is also more common than SJIA: about 1 in 4 children with JIA have PJIA, while only 1 in 10 with JIA have SJIA. Girls tend to get PJIA more than boys do, but both may develop SJIA at about the same rate.
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