Types of Juvenile Idiopathic Arthritis (JIA)
There are multiple types of JIA, each with distinct features. Generally, they all share arthritic symptoms of joint pain, swelling, warmth, and stiffness that last at least 6 weeks.
The types are:
- Oligoarticular juvenile idiopathic arthritis. This isthe most common form of JIA in North America and the mildest form, affecting four or fewer joints. It is considered persistent if symptoms continue for 6 months or longer, and extended if five or more joints become involved after 6 months of illness. Commonly affected joints are knees or ankles. A form of eye inflammation called chronic (long-lasting) uveitis can develop in children with this form of JIA, especially girls who develop this form of JIA at a young age (6 years of age or less) and have a positive autoantibody called anti-nuclear antibody. Due to the risk of uveitis in children with oligoarticular JIA, patients need to have an eye exam with an ophthalmologist regularly. About half of children in North America with JIA have this type.
- Polyarticular juvenile idiopathic arthritis-rheumatoid factor negative. Thisis the second most common type, affecting five or more joints in the first 6 months.Tests for rheumatoid factor are negative. The rheumatoid factor blood test checks for autoimmune disease, especially rheumatoid arthritis, which is an adult form of arthritis. Some children with this type develop chronic uveitis, especially girls who develop polyarticular JIA at a young age and have a positive anti-nuclear antibody.
- Polyarticular juvenile idiopathic arthritis-rheumatoid factor positive. A child with this type has arthritis in five or more joints during the first 6 months. Tests for rheumatoid factor are positive. It tends to occur in preteen and teenage girls, and it appears to be essentially the same as adults with rheumatoid arthritis who have certain autoantibodies called rheumatoid factor and anti-citrullinated protein antibodies.
- Enthesitis-related juvenile idiopathic arthritis. This form of JIA involves both arthritis and enthesitis. Enthesitis happens when inflammation occurs where a ligament or tendon attaches to a bone. The most common locations for enthesitis are the knees, heels, and bottoms of the feet. Arthritis is usually in the hips, knees, ankles, and feet, but the sacroiliac joints (at the base of the back) and spinal joints can also become inflamed. Some children get episodes of acute anterior uveitis, a sudden onset of inflammation of the front of the eye. Unlike most other forms of JIA, enthesitis-related JIA is more common in boys.
- Psoriatic juvenile idiopathic arthritis. Children with this type may have psoriasis, a skin condition, as well as inflammation of the joints. The skin condition usually appears first, but sometimes painful, stiff joints are the first sign, with the skin disease occurring years later. Pitted fingernails and dactylitis (swollen fingers or toes) are also signs of the disease.
- Systemic juvenile idiopathic arthritis. Systemic means the disease can affect the whole body, not just a specific organ or joint. Systemic JIA usually starts with fever and rash that come and go over the span of at least 2 weeks. In many cases, the joints become inflamed, but sometimes not until long after the fever goes away, and sometimes not at all if treatment is started quickly. In severe forms, inflammation can develop in and around organs, such as the spleen, lymph nodes, liver, and linings of the heart and lungs. Systemic JIA affects boys and girls equally.
- Undifferentiated arthritis. This category includes children who have symptoms that do not fit into any of the other types or that fit into more than one type.
