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Juvenile arthritis, also known as juvenile idiopathic arthritis, is not one condition but a group of related autoimmune conditions that occur for unknown reasons in children and adolescents. In autoimmune conditions, the body’s immune system attacks healthy cells instead of protecting them from disease or infection.

The most common forms of juvenile arthritis, all of which cause chronic, or long-term, inflammation and pain in the joints and other parts of the body, are categorized according to the symptoms they cause.

Oligoarticular Arthritis

Oligoarticular arthritis is the most common and mildest form of juvenile arthritis. Children with oligoarticular arthritis develop inflammation and swelling in a few of the larger joints, such as the knees, ankles, and wrists. Many children with this condition also develop uveitis, an inflammation of the middle layer of the eye, which includes the iris. Uveitis usually causes no symptoms but can lead to vision problems over time.

Although symptoms are not usually severe, oligoarticular arthritis can slow a child’s growth and cause joint damage if not detected and treated promptly. Oligoarticular arthritis is more common in girls than in boys. 

Polyarticular Arthritis 

Polyarticular arthritis affects many joints throughout the body, including small joints in the hands and feet and large joints, such as knees, hips, and ankles. Symptoms of this condition, which is more common in girls, are similar to those of adult rheumatoid arthritis.

Children with polyarticular arthritis who also are found to have rheumatoid factor in their blood—an antibody that signals the body to attack its own tissues—are more likely to have symptoms throughout adulthood and develop joint damage.  

Systemic Arthritis

Systemic arthritis, also called Still’s disease, affects boys and girls equally. The condition often begins with a high fever and a pink rash on the body, arms, and legs. Joint inflammation, which usually develops within the first six months after the fever, doesn’t always occur at the onset of this condition.

Children with severe systemic arthritis may also develop inflammation in and around organs, such as the heart, lungs, liver, gastrointestinal tract, spleen, and lymph nodes, which can cause chest pain, breathing problems, abdominal pain, and fatigue. In some instances, children with systemic arthritis may be unable to form new blood cells in the bone marrow. 

Enthesitis-Related Arthritis 

Some children with juvenile arthritis develop enthesitis, which is an inflammation that occurs at the point where the tendons and ligaments—flexible bands of soft tissue—connect to the bones of the ankles, feet, and spine. Children with this form of arthritis may also have some joint swelling.

Enthesitis-related arthritis is more common in boys and tends to affect joints in the spine and hip. The most severe forms of this condition are known as spondyloarthritis, a group of arthritis conditions, including ankylosing spondylitis, that can cause pain and inflammation in the joint that connects the hip bones to the spine.

Psoriatic Arthritis

Children with psoriatic arthritis have psoriasis—an autoimmune condition that causes a red, scaly skin rash and pitted fingernails—and inflammation in the joints. Some children with this condition experience the symptoms of psoriasis first, whereas others first experience joint inflammation. Psoriatic arthritis is more common in children who have a family history of psoriasis.