Juvenile Idiopathic Arthritis (JIA)

Considered the most common form of arthritis, juvenile idiopathic arthritis (JIA) begins before age 16 and involves swelling in one or more joints lasting at least six weeks. JIA, which includes several types of arthritis previously known as juvenile rheumatoid arthritis, may include a variety of symptoms, such as muscle and soft tissue tightening, bone erosion, joint misalignment and changes in growth patterns.

In addition to watching for symptoms for at least six weeks, your child’s doctor will wait to see how her symptoms unfold during the first six months after onset. As with the previous JRA criteria, the number of joints affected during those first six months determines the diagnosis. In addition, the JIA criteria also rely on other results, such as those from the rheumatoid factor blood test, to help further stratify patients.

Based on her symptoms, your child may be diagnosed with one of the following categories of JIA:  

Oligoarthritis: Formerly known as pauciarticular this type, is diagnosed when four or fewer joints – “pauci” and “oligo” mean “few” – are involved within the first six months. It’s particularly common in Caucasian children and accounts for about 40 percent of new JIA cases in that group. Girls are more likely to be diagnosed with oligoarthritis and to experience eye inflammation, a condition called uveitis. Oligoarthritis typically develops by age 6. At diagnosis, frequently only one joint is involved and it’s commonly a joint in the leg, such as the knee or the ankle.

If your child also tests positive for a particular antibody in the blood, called the antinuclear antibody (ANA), she faces the greatest risk of developing eye inflammation and will be monitored very closely for eye problems. Compared with other types of JIA, children with oligoarthritis are less vulnerable to severe problems with joint function.

Under the JIA criteria, oligoarthritis is broken into two groups. Children in which the arthritis is confined to four or fewer limbs fall into a category called persistent oligoarthritis. After the six-month window, some children will develop symptoms in additional limbs and will be diagnosed with extended oligoarthritis.

Polyarthritis: This type of JIA – “poly” means “many” – occurs when five or more joints are involved during the first six months. Roughly 25 percent of children with JIA have polyarthritis. Like oligoarthritis, it’s more common in girls. But its onset can occur any time in childhood. Both large and small joints, such as the fingers and toes, may be involved. Your child also may experience arthritis in the neck or the jaw, making chewing and opening her mouth more difficult.

Unlike oligoarthritis, polyarthritis more frequently affects joints on both sides of the body, such as the right and the left knees. Children with polyarthritis might face a lower risk of eye inflammation, but will still need to see an ophthalmologist on a regular basis.