Juvenile idiopathic arthritis (JIA), previously known as juvenile rheumatoid arthritis, is a type of joint inflammation that occurs in children and adolescents before the age of 16, causing joint pain, stiffness, and swelling for more than six weeks. The term, “idiopathic,” means of unknown cause, although juvenile idiopathic arthritis is thought to be an autoimmune disorder, affecting females more than males. Nearly 50% of children and adolescents will outgrow the disease; however, it can still cause lasting joint damage.
There are several types of juvenile idiopathic arthritis, which are determined by their symptoms, the affected joints, lab tests, and family history, and which include the following:
Systemic juvenile idiopathic arthritis – This type of juvenile idiopathic arthritis affects one or more joints, causing joint inflammation accompanied by a fever that lasts at least two weeks. In addition, systemic juvenile idiopathic arthritis may also be accompanied by a skin rash, or enlarged lymph nodes, lungs, liver, or spleen.
Oligoarticular juvenile idiopathic arthritis (Oligoarthritis) – This type of juvenile idiopathic arthritis is the most common type (more than 50%) and occurs in four joints or less during the first six months of the disease and has two subtypes: 1) persistent oligoarthritis (four affected joints or less after six months); and 2) extended oligoarthritis (more than four affected joints after six months). Individuals with oligoarthritis have an increased risk of developing eye inflammation (uveitis or iridocyclitis).
Rheumatoid factor positive polyarticular juvenile idiopathic arthritis (Polyarthritis) – This type of juvenile idiopathic arthritis affects more than five joints, usually the fingers or toes, during the first six months of the disease and is similar to adult rheumatoid arthritis, as patients with this type test positive for rheumatoid factor and may develop small bumps near joints (rheumatoid nodules).
Rheumatoid factor negative polyarticular juvenile idiopathic arthritis (also called Polyarthritis) – This type of juvenile idiopathic arthritis affects five or more joints during the first six months of the disease; however, patients with this type test negative for rheumatoid factor.
Psoriatic juvenile idiopathic arthritis – This type of juvenile idiopathic arthritis occurs alongside psoriasis, a skin disorder which is characterized by reddened skin plaques (patches) covered with white scales and which can also include nail abnormalities (pitting) and eye inflammation.
Enthesitis-related juvenile idiopathic arthritis (Juvenile spondyloarthritis) – This type of juvenile idiopathic arthritis affects the areas where bone connects with tendons, ligaments, or other connective tissue, usually in the hips, knees, or feet, causing tenderness (enthesitis), along with joint inflammation, and may affect other areas of the body, such as the eyes (uveitis), and is more common in males than females.
Reactive arthritis (Reiter’s syndrome) – This type of arthritis develops as a reaction to bacterial infections, such as shigella, salmonella, yersinia, or genitourinary chlamydial infection (sexually transmitted disease), and occurs abruptly, causing fever, joint pain and inflammation, painful urination, and eye infection (conjunctivitis).
Juvenile systemic lupus erythematosus (Lupus) – This disease can cause joint inflammation in addition to inflammation in several other areas of the body.
Undifferentiated arthritis – This type of juvenile idiopathic arthritis covers any type that does not fall into the above categories.