What Are the Types of Juvenile Idiopathic Arthritis (JIA)?
Oligoarticular JIA
Oligoarticular JIA is the most common form of juvenile idiopathic arthritis. Oligo means few in Latin. By definition, this form of JIA has four or less joints involved during the first six months of disease. About 40% of patients with oligoarticular JIA will go on to develop arthritis in more than four joints over the course of the next few months to years. This is sometimes called extended oligoarticular JIA.
Oligoarticular JIA usually occurs with young girls (1-5 years old) or in boys in late school age or adolescence. For young girls with oligoarticular JIA, onset is often before the age of 5. The most common joint to be involved is the knee, and these patients usually have a positive ANA. These young girls with limited joint involvement and positive ANA are in the group of patients at highest risk to develop inflammation in the eye (up to 30%). The eye inflammation is called iritis or iridocyclitis (ear-ri-do-si-cli-tis). For this reason, this group of children is checked by the ophthalmologist more frequently for possible inflammation in the eye. The highest risk of getting eye inflammation is within seven years of developing the arthritis. Visits to the eye doctor are usually three to four times per year, even if no symptoms affect the eyes. For these boys with oligoarticular JIA it is believed that there is a link between this group of children and a family of arthritic conditions called spondyloarthropathies. "Spondylo" means spine; "arthropathy" means affecting the joint. Together these mean male children or adolescents can develop arthritis in the back or spine area. In patients who have arthritis in the spine, the disease is called juvenile ankylosing spondylitis. If there is not arthritis in the spine, then that diagnosis cannot be made yet. The common link is a gene called HLA-B27. Patients with a spondyloarthropathy commonly have HLA-B27. About 60-80% of the young boys with oligoarticular JIA have the HLA-B27 gene. Not all of these boys (sometimes girls) will go on to develop ankylosing spondylitis however.
These patients can have joint inflammation in the hips, knees, ankles, toes and shoulders. Involvement in the hands, wrists and elbows is much less common. Inflammation may also occur in the heels and tendons (sometimes called enthesitis related arthritis where an enthesis is a tendon or ligament). Some of these patients could develop inflammation in the small intestine or colon. It is important for this group of children to be aware of symptoms related to their bowels. If abdominal pain and diarrhea occur, attention can be directed to proper diagnosis and treatment. The other symptom to watch for is sudden inflammation in the eye. This form of eye inflammation is quite painful and is usually brought promptly to the attention of the doctor.
Iridocyclitis – Uveitis, Iritis
Children and adolescents with JIA are susceptible to developing inflammation in the eye as well as the joints. The children at highest risk are the little girls with the fewest joints involved. Most children who get eye disease get it within seven years of the onset of their arthritis.
The inflammation is located in the front of the eye in the part called the iris (colored part of the eye) and in the ciliary body. The term for the eye inflammation is called iridocyclitis or Uveitis. In over 80% of children with JIA who get uveitis there are absolutely no symptoms and the only way it can be found is by the eye doctor looking at the eyes. If the child does have symptoms then it is blurry vision, pink eye, squinting, or pain. Since few or no symptoms happen we must check for the inflammation on a regular basis before the eye is damaged and there are changes in vision. If there is inflammation the ophthalmologist will prescribe eye drops. Treatment for the eyes is separate from the treatment for the joints.
A slit lamp examination by the ophthalmologist is a brief, easy, painless test to perform even on young children and is the best way to detect the eye inflammation seen in children with JIA. The slit lamp needs to be done at regular intervals for several years, depending on which type of JIA your child has. The rheumatologist will tell you how often to get the slit lamp test.
The eye inflammation is independent or separate from the arthritis. This means one symptom can be active and the other can be in remission or not present. It is important for you to help keep track of the eye examinations.
Polyarticular JIA
Polyarticular JIA, by definition, involves five or more joints in the first six months. "Poly" means many. Patients with polyarticular JIA usually have involvement of both large and small joints. This means that any joint (the neck, jaws, fingers, toes and all the other large joints) can get inflammation. Arthritis in the low and mid-back would be uncommon. However, the neck (or cervical spine) is commonly involved in this subtype. Patients with polyarticular JIA can have some systemic features, such as low-grade fever, weight loss, reduced appetite, mild lymph node enlargement and low-grade anemia. Problems of the heart, lung, and kidney are rare. However, we will watch for involvement in other areas of the body in addition to the joints.
At most one out of 10 (10%) children who have polyarticular JIA will have a positive rheumatoid factor blood test. Most adults with rheumatoid arthritis do have a positive rheumatoid factor. The presence of rheumatoid factor in a child with polyarticular JIA suggests that these children may have disease that is very similar to adult rheumatoid arthritis. These children (mostly girls with onset of disease during late school age or adolescence) may have the other features of adult rheumatoid arthritis. These would include rheumatoid nodules and the potential for inflammation in small joints. We will talk with you more about these features if they occur.
Polyarticular JIA patients are at less risk for developing eye inflammation than patients with oligoarticular JIA. Inflammation in the eye can occur in about five out of 100 polyarticular JIA patients. This means that slit lamp examinations by the ophthalmologist need to be done every 6-12 months for the first few years of disease.
Systemic JIA
Systemic JIA is the form of juvenile idiopathic arthritis which affects the entire body or "system," often before it affects the joints. The most common symptom is a high fever which usually happens once or twice a day. The fever is usually quite high with temperatures 103° or higher. This fever typically occurs in the late afternoon or the evening. During the fever, your child can look quite ill. When your child is not feverish, there will be fewer signs or symptoms of the disease.
During the times of fever, there is often a rash. This rash comes and goes. Only about one in 20 children will complain of any itching with the rash. The rash is not contagious. The rash is often present when there is pressure on the skin. An example is under the elastic of the undergarments or where the skin has been scratched. The rash also comes out whenever the skin is hot from exercise or environmental temperature. Even getting a warm bath and drying off with the towel may bring out the rash. The rash lasts only a short time and then goes away completely or moves to another part of the body. The rash does not cause any damage or permanent changes to the skin.
The lymph nodes, liver, and spleen are organs which react to the inflammation. They can become enlarged in about six out of 10 children. The enlargement is not dangerous. However, it is part of the disease and needs to be understood.
Eventually, most children will develop arthritis in at least a few joints. At the beginning of the illness it can come and go with the systemic features. It is not possible to project a prognosis regarding the joints until some time has gone by and the course of your child's disease becomes apparent.
Most patients with systemic JIA become quite anemic over the course of the first few weeks of inflammation. This anemia can be severe in some patients but rarely requires transfusion. Usually, the white blood count and the platelets are very high.
Usually the systemic features of systemic JIA last for several weeks to several months. It is unusual for the systemic features to last indefinitely; however, this does occur in rare cases.
Inflammation of the outer lining of the heart, the pericardium, occurs in some children with systemic JIA. However, only in a small group of children does it become serious with chest pain, shortness of breath, and pressure in the chest. If this would occur, it is important to notify the doctor or nurse as soon as possible so that it can be evaluated and treatment can be started if necessary. Fortunately, involvement of the heart muscle is rare.
