Juvenile idiopathic arthritis (JIA)

JIA is the most common type of long-lasting (chronic) arthritis in children. Arthritis means inflammation of the joints. JIA begins before the 16th birthday and causes joint pain, swelling, warmth and stiffness that last at least 6 weeks. “Idiopathic” means the cause is not known.

JIA is a group of diseases, not just one. The types include oligoarticular JIA (4 or fewer joints, the most common type in North America), polyarticular JIA (5 or more joints), enthesitis-related JIA, psoriatic JIA, systemic JIA and undifferentiated arthritis. JIA was once called juvenile rheumatoid arthritis (JRA) or juvenile chronic arthritis.

Systemic JIA is different from the other types. It affects the whole body, with daily fevers and a rash that come and go, and sometimes inflammation of the spleen, lymph nodes, liver and the linings of the heart and lungs. It is also known as Still’s disease. Many of the children who have had a stem cell transplant for JIA had systemic JIA.

In JIA, the immune system mistakenly attacks the body’s own healthy tissues, which causes inflammation. Scientists do not know why this happens. They think a complex mix of genes and things in the environment is involved. Signaling molecules called TNF-alpha, IL-1 and IL-6 help drive the inflammation, and this knowledge led to medicines that block them.

It is very rare for more than one person in a family to have JIA. Children with a relative who has long-lasting inflammatory arthritis have a slightly higher chance of getting it. Some families also have other autoimmune conditions, such as psoriasis, inflammatory bowel disease, thyroid disease, celiac disease or type 1 diabetes. Normal variations in HLA genes, which help the immune system tell the body’s own proteins from germs, affect the risk and the type of JIA.

Some experts consider systemic JIA an autoinflammatory disorder. The immune signals that drive it differ from those in other types of JIA.

Joint symptoms are often worse in the morning or after a nap or sitting for a long time. Young children may not complain of pain, but they may limp in the morning. Symptoms can come in flares that last weeks or months, with calmer times in between. Some children have only one or two flares, while others have symptoms that never fully go away.

JIA can affect more than the joints. Eye inflammation (uveitis) can have no symptoms but can lead to cataracts, glaucoma and vision loss if it is not treated, so children need regular eye exams. Inflammation can also slow growth, make one arm or leg longer than the other, or lead to a small or misshapen chin.

Systemic JIA can cause serious complications. Macrophage activation syndrome (MAS) is a life-threatening storm of immune activity. It causes fever, very high ferritin, low blood counts and abnormal liver tests. A 2025 study says it happens in about 1 or 2 of every 10 children with systemic JIA. U.S. guidelines say up to 4 in 10 cases of systemic JIA are linked to MAS. A rare lung disease linked to systemic JIA (sJIA-LD) has also been recognized. In one study of 41 children with it, 15 came to need long-term oxygen or breathing support within a middle follow-up of about 3 years.

No single test diagnoses JIA. Doctors suspect it when a child under 16 has joint pain, stiffness or swelling that has lasted at least 6 weeks without another explanation. They diagnose it mainly by ruling out conditions that look similar, such as an infection, a broken bone or a tumor.

Blood tests help. Markers of inflammation (ESR and CRP) are often high in systemic JIA. A positive antinuclear antibody (ANA) test points to a higher risk of eye inflammation. Rheumatoid factor and anti-CCP antibodies are rare in JIA; when present, they usually mean rheumatoid factor-positive polyarticular JIA. HLA-B27 is a risk factor for enthesitis-related JIA. X-rays, ultrasound and MRI show inflammation and joint damage, and an eye doctor checks for uveitis.

Systemic JIA can be harder to recognize, because fever and rash can come before any arthritis, sometimes long before. Doctors also watch for MAS, which shows up as fever, a high ferritin level, falling blood counts, abnormal liver tests and low fibrinogen, because it needs urgent treatment.

The goals are to control pain and inflammation, protect the joints, support normal growth and development, and reach remission. Doctors usually treat JIA strongly at first and then slowly reduce medicines once remission is reached. Treatment may include anti-inflammatory medicines, steroid shots into a joint, disease-modifying medicines (DMARDs) and biologic medicines that block TNF-alpha, IL-1 or IL-6. Physical therapy helps keep joints moving.

For systemic JIA without MAS, 2021 guidelines from the American College of Rheumatology (ACR) suggest starting with an IL-1 or IL-6 blocker, with no preferred one. In the U.S., canakinumab (an IL-1 blocker) and tocilizumab (an IL-6 blocker) are approved for systemic JIA. In June 2025, the FDA approved emapalumab (Gamifant) for MAS, a form of HLH, in Still’s disease, including systemic JIA. It is for children and adults when steroids have not worked well enough or are not tolerated, or when MAS keeps coming back.

Many children respond well to these medicines. Still, a 2022 review estimated that about 1 in 7 children with systemic JIA have active disease over the long term, even with biologic medicines. Disease that stays active despite IL-1 or IL-6 blockers, or that needs steroids for more than 6 months, is called refractory. Care teams then try other medicines or combinations.

A stem cell transplant is considered only for a few children with the most severe disease. In their 2025 recommendations, European transplant experts (EBMT) list both own-cell (autologous) and donor (allogeneic) transplants as clinical options, meaning they can be done after careful weighing of risks and benefits. Own-cell transplants were used first, starting in 1997. Many children improved, but some died of MAS or infections, and in some the disease came back, sometimes years later. More recent reports use donor cells with gentler preparation.

JIA affects the whole family. Children are often cared for by a team: a pediatric rheumatologist, an eye doctor, physical and occupational therapists, and sometimes mental health professionals and social workers who can work with the school. Regular visits let the team check how treatment is working and adjust it.

Many JIA medicines are given as shots under the skin or into a vein. NIAMS describes more rest when JIA is active and more exercise when it is not, to keep muscles strong and joints flexible, and notes that swimming uses many joints without stressing them. For some people, JIA lasts into adulthood and still needs treatment then.

For the rare child who has a transplant, the process includes strong medicines to prepare the body and a recovery period with a high risk of infection. In the first own-cell transplant program, some early deaths were linked to MAS. The program then added better control of the disease before transplant, among other changes. No more transplant-related deaths were seen in the 11 children treated after that change (published 2007).

Most children with JIA never need a donor. The first transplants for JIA used the child’s own stem cells, so no donor was involved.

Recent transplants for the most severe systemic JIA have used donor cells. In the 2025 study of 13 children with systemic JIA and lung disease, 11 received cells from unrelated donors: 6 fully matched and 5 partly matched. One child’s donor was a matched brother or sister, and one was a partly matched relative. European experts (EBMT, 2025) list a matched brother or sister and a well-matched unrelated donor as clinical options, and partly matched donors as an option with less evidence.

Because very few children need this, JIA is not a common reason for a donor search. Joining an official donor registry is a way to help any patient who needs a match, including the rare child with severe systemic JIA.

With treatment, most children with JIA have times with no symptoms and no active disease (remission), and sometimes the disease goes away for good. For others, JIA is lifelong and needs treatment into adulthood. NIAMS says early treatment matters, because delay can lead to joint damage and a weaker response to treatment.

Long-term studies show that many young adults still have some disease. A 2025 review found that in all but one long-term study, fewer than half of people were in remission without medicine as adults. Only one of those studies included only children diagnosed after biologic medicines came into use.

Refractory systemic JIA with repeated MAS or lung disease can be life-threatening. For some of these children, a donor transplant has led to remission, but the transplant itself carries a real risk of death.