There are 7 main types of JIA, but as is so often the case categorising conditions is not always easy and very often there is overlap between the different categories.

On this page, we cover:

We also have a more detailed medical description of JIA

We also have information on two serious conditions associated with JIA


  • Uveitis
    Inflammation of the internal lining of the eye is called and is a potentially serious complication of JIA. Regular eye screening is essential to detect its presence at an early stage, as patients remain symptom free until the eye suffers significant and sometimes irreversible damage.  Read more about Uveitis.
  • Macrophage Activation Syndrome (MAS)
    MAS is a rare but potentially life threatening complication associated with Systemic Onset JIA and other rheumatological conditions. In MAS, for reasons we don’t fully understand, there is over activation and unregulated production of certain cells of the immune system.  Read more about MAS.

Oligoarthritis – the most common type of JIA

  • Oligoarthritis affects about two-thirds of children and young people with arthritis and most commonly affects one or both knees.
  • This form of arthritis is often mild and is the most likely type of JIA to go away and leave little or no damage to your joints.
  • This type of arthritis has the highest chance of you developing chronic anterior uveitis (inflammation of the eye), so you’ll need regular eye checks with an ophthalmologist (eye specialist). This eye inflammation doesn’t cause a red or painful eye but can still cause reduced vision if it isn’t treated. This is why regular checks are important.

Extended Oligoarthritis

  • With this form of JIA, you have Oligoarthritis in the first 6 months and then develop problems with many joints (5 or more) after that.
  • This type of JIA can cause damage to your joints and your doctor may suggest early treatment with drugs like methotrexate to keep this damage to a minimum.

Polyarthritis JIA – the second most common type of JIA

  • This type of JIA tends to cause painful swelling in fingers, toes, wrists, ankles, hips, knees, and the neck and jaw.
  • It may come on suddenly or can steadily involve more joints over a period of months.
  • You may feel unwell and tired and occasionally develop a slight fever.
  • The symptoms may continue into adult life but it can go into a state where all the symptoms disappear. This is called remission.
  • A blood test will show whether a marker called rheumatoid factor is present in your blood.

Enthesitis-related JIA

  • This form of JIA affects the places where tendons attach to the bone (these places are called entheses), causing inflammation. It often affects the joints of the leg and spine.
  • In contrast to the uveitis seen with the other types of JIA, this type of JIA is associated with a red painful eye – acute uveitis.
  • Stiffness in the neck and lower back may develop in the teens or as a young adult.
  • There may be a family history of ankylosing spondylitis or inflammatory bowel disease because of a particular genetic marker called HLA-B27.

Psoriatic arthritis

Psoriasis is a common skin condition which typically causes patches of red, scaly skin to develop. Psoriatic arthritis is a particular type of arthritis that develops in some people who also have psoriasis.

Systemic-onset JIA – the rarest type of JIA

  • In this form of arthritis, joint pain is part of a general illness involving fever, tiredness, rash, loss of appetite and weight loss.
  • There may be enlarged glands in the neck, under the arms and around the groin area.  The spleen and liver may become enlarged, and, very occasionally, the covering of the heart is inflamed (pericarditis).
  • In the first few weeks there may be no sign of swollen joints, and the diagnosis may be uncertain. Lots of tests may be needed to confirm the diagnosis and this can be a worrying time.
  • The long-term development of this form of JIA can be difficult to predict but with treatment usually the fever and rash will settle, although the arthritis may sometimes continue for several years before settling.

Systemic JIA patients have the greatest risk of developing Macrophage Activation Syndrome.

Undifferentiated arthritis

Sometimes young people don’t fit neatly into the other JIA groups and the condition is defined as undifferentiated arthritis. It may not seem a very useful category, but it’s one that doctors sometimes have to use.

Medical description of JIA

Juvenile Idiopathic Arthritis (JIA) is a chronic inflammatory disorder of the body joints affecting about 1⁄1000 children and adolescents under 16 years of age.
There are several causes of joint inflammation such as an injury or infection of the joint itself (septic arthritis) or more frequently infection somewhere else in the body (reactive arthritis) such as a streptococcal throat infection or gastroenteritis. These trigger the release of cytokines (mediators of inflammation) such as TNF within the joint which induce and perpetuate the inflammation. There is an increased blood flow though the lining of the joint (synovium) which becomes swollen and produces excess joint fluid.
Reactive arthritis usually resolves within a month from onset.

In JIA no trigger is identified but the inflammation persists beyond 6 weeks. The child complains of pain in the affected joint ⁄ joints, which become stiff on waking up in the morning and after periods of inactivity. They are swollen and warm and fluid may be elicited in the larger joints (eg: knee).
The arthritis may affect a few joints (oligoarthritis) or many joints (polyarthritis). It may spread to other joints (extended oligoarthritis).

JIA is different from adult rheumatoid arthritis. Only about 5% of cases test positive for rheumatoid factor (or anti CCP, a newer marker of RA in adults)) in the blood and have a disease course similar to that in adult rheumatoid arthritis.

Arthritis may be the presenting manifestation in psoriasis and in enthesitis related arthritis (ERA), which is the paediatric equivalent of ankylosing spondylitis in adults.

Systemic Onset JIA can be difficult to diagnose initially as it presents with fever and rash resembling a viral infection. The arthritis, usually involving small and large joints, may present weeks or months later.

Arthritis is also seen in children with a variety of conditions including Down’s syndrome and inflammatory bowel disease.

The diagnosis of JIA is made after a detailed history and examination. There is no diagnostic test. Some investigations, such as blood picture and xrays are done mainly to exclude other causes of arthritis. Other investigations, such as the inflammatory markers ESR and CRP, are useful in monitoring the disease course although not in every case.
The autoantibodies ANA ( anti-nuclear antibody) and RF (rheumatoid factor; often now replaced by a test called anti-CCP)) may be helpful in determining which subtype of JIA a child has and giving a prognosis on the severity and duration of JIA.
Patients with ERA are likely to have an HLA B27 positive tissue type.
Ultrasound and MRI scans give useful information on the extent of inflammation in the joints.

Inflammation of the internal lining of the eye (uveitis) is a potentially serious complication of JIA. It is more common in female patients especially those who are ANA positive and in patients with oligoarthritis. Regular eye screening is essential to detect its presence at an early stage, as patients remain symptom free until the eye suffers significant and sometimes irreversible damage.

The treatment of JIA aims at the rapid suppression of inflammation in the joints, best achieved with intra-articular steroid injections, together with the suppression of the underlying autoimmune process by the administration of immunosuppressants such as methotrexate.
The biological agents Etanercept, Infliximab and Adalimumab block TNF, the main cytokine inducing synovial inflammation. Tocilizumab which blocks a different cytokine (IL-6) is now being used more commonly in both systemic onset and polyarticular JIA and other biologics such as abatacept (works on the T cells in the immune system) and rituximab (blocks the cells which produce antibodies) may be helpful in children and young people who have not settled with other treatments.

Physiotherapy and hydrotherapy are useful aids in helping the child with JIA by building up the muscles and keeping the affected joint⁄s supple. Occupational therapists give useful advice on how to cope with any restrictions imposed on body movements by the arthritis.

The prognosis and severity of arthritis varies with the JIA subtype. In general the more the number of joints involved the longer is the duration of JIA and the greater is the chance of arthritis continuing beyond puberty; but the smaller the chance of developing uveitis.

Although a cure is not available, modern advances in therapy allow good disease control and prevent long term joint and eye damage in most patients.

This article was written by Dr P Galea, Consultant Paediatric Rheumatologist, Yorkhill Hospital, Glasgow in May 2010 and reviewed and updated September 2014).