Juvenile Idiopathic Arthritis
Juvenile idiopathic arthritis (JIA) is the most common type of arthritis that affects children. It used to be known as juvenile rheumatoid arthritis, but the name was recently changed to reflect the differences between childhood arthritis and adult forms of rheumatoid arthritis.

JIA is a chronic (long-lasting) disease that can affect joints in any part of the body. In this disease, the immune system mistakenly targets the synovium, the tissue that lines the inside of the joint. The synovium responds by making excess fluid (synovial fluid), which leads to swelling, pain and stiffness. The synovium and inflammation process can spread to the surrounding tissues, eventually damaging cartilage and bone. Other areas of the body, especially the eyes, also may be affected by the inflammation. Without treatment, JIA can interfere with a child’s normal growth and development.

There are several main subtypes of JIA, which are based on symptoms and the number of joints involved.

Systemic arthritis - Also called Still’s disease, this type occurs in about 10 to 20 percent of children with JIA. A systemic illness is one that can affect the entire person or many body systems. Systemic JIA usually causes a high fever and a rash, which most often appears on the trunk, arms and legs. It also can affect internal organs, such as the heart, liver, spleen and lymph nodes. This type of JIA affects boys and girls equally and rarely affects the eyes.

Oligoarthritis - This type of JIA affects fewer than 5 joints in the first 6 months of disease, most often the knee, ankle and wrist joints. It also can cause inflammation of the eye (often the iris, the colored area of the eye), called uveitis, iridocyclitis or iritis. About half of all children with JIA have this type, and it is more common in girls than in boys. Many children will outgrow this type of arthritis by adulthood. In some children it may spread to eventually involve more joints.

Polyarthritis - This type of JIA affects 5 or more joints in the first 6 months, often the same joints on each side of the body. Polyarthritis can also affect the neck and jaw joints as well as small joints, such as those in the hands and feet. It is more common in girls than in boys.

Psoriatic arthritis - This type of arthritis affects children who have arthritis with the rash of psoriasis. Children frequently have nail changes that look like pitting. The arthritis can precede the rash by many years or vice versa.

Enthesitis-related arthritis - This type of arthritis often affects the spine, hips and enthesis (attachment point of tendons to bones) and occurs mainly in boys older than 8 years. The eyes are often affected in this type of arthritis. There is often a family history of arthritis of the back (spondylitis) in male relatives.