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Types of JIA
Oligoarthritis
Oligoarthritis is the most common type of JIA, affecting about two-thirds of children and young people with arthritis. It most commonly affects the knees, though other joints (such as the ankles) also may be affected. Its effects usually are very mild, and the condition can disappear on its own without causing lasting damage.
Children with oligoarthritis have the highest chance of developing uveitis, and they should receive regular checks from an ophthalmologist.
Extended Oligoarthritis
Extended oligoarthritis is a type of JIA that first presents as oligoarthritis and then—usually after approximately six months—develops into a more widespread and significant condition.
Children with extended oligoarthritis regularly experience symptoms in five or more joints, which can be permanently damaged without treatment. To minimise this damage, patients with this type of JIA may be treated with methotrexate.
Polyarthritis JIA
This common type of JIA—sometimes called polyarticular arthritis—affects joints throughout the body. It also can cause patients to develop a slight fever and generally to feel unwell.
Polyarthritis JIA may come on suddenly, develop gradually, and endure into adulthood. Some children with this condition, however, will go into remission.
A blood test can show whether a marker called rheumatoid factor is present in children with polyarthritis JIA.
Enthesitis-related JIA
This type of JIA causes enthesitis, or inflammation in the entheses (places in the body where tendons attach to bones). It typically affects the heel and arch of the foot or the hips; early signs of the condition may include stiffness in the neck and lower back. Children with this condition are at risk of developing acute uveitis.
In diagnosing enthesitis-related JIA, doctors may look for a family history of ankylosing spondylitis or inflammatory bowel disease, and they may also test for the HLA-B27 gene.
Psoriatic arthritis
Psoriatic arthritis develops in some children who have (or have a family history of) psoriasis—a common skin condition that typically causes patches of red, scaly skin.
Systemic JIA
In this rare form of arthritis, joint pain is part of a general illness with a wide range of possible effects, including:
- Fever
- Fatigue
- Rash
- Loss of appetite and weight loss
- Enlarged glands in the neck, under the arms, and in the groin
- Enlargement or inflammation of the spleen, liver, and—in some very rare cases—the pericardium (the membrane covering the heart).
It is not always easy to diagnose a case of systemic JIA. In the first few weeks, there may be no sign of swollen joints, and multiple tests may be required to confirm the diagnosis. This can be an uncertain and anxious time for children and parents alike.
Patients with systemic JIA are less likely to respond to methotrexate alone. Initial treatment usually involves a course of steroids, delivered as an infusion (drip) for at least three days. Patients with systemic JIA will often respond very well to Anakinra or Tocilizumab, and it is likely your doctor will recommend using one of these modern ‘biologic’ drugs as the main treatment for systemic JIA to control the inflammation and allow steroids to be reduced and stopped as soon as possible.
Children with systemic JIA face a small risk of developing Macrophage Activation Syndrome.
Undifferentiated arthritis
This is not so much a discrete type of JIA as a name for those cases that do not fit neatly into any other category.