Subtypes of Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is an umbrella term for autoimmune or autoinflammatory types of arthritis in children. It used to be called juvenile rheumatoid arthritis (JRA) and had three recognized types.

Now, the International League of Associations for Rheumatology (ILAR) has divided JIA into seven subtypes. This was done primarily for research purposes and may change again as researchers learned more about the genetics and course of the disease in children.

However, the name JRA was also misleading in many cases, as JIA isn't a juvenile form of adult rheumatoid arthritis.

Arthritis is simply pain, stiffness, and inflammation in a joint. Idiopathic means it has an unknown cause.

Oligoarthritis

Oligoarthritis is the most common form, affecting between 30% and 60% of children with JIA.

These kids have arthritis affecting one to four joints within the first six months of disease.

If they continue having symptoms in four or fewer joints later on, it's called persistent oligoarthritis. If their pain spreads to more joints down the road, it's called extended oligoarthritis.

Polyarticular RF-Negative

"Poly" means many, so "polyarticular" impacts many joints.

Rheumatoid factor (RF) is an autoantibody, which the immune system creates to attack and destroy a healthy part of your body as if it were a virus or other pathogen. RF attacks the lining of the joints.

A child is diagnosed with polyarticular RF-negative when they meet three criteria:

1. Arthritis in five or more joints
2. In the first six months of the disease
3. And negative RF tests

This type of arthritis affects between 10% and 30% of children with JIA.

Polyarticular RF-Positive

Children are diagnosed with polyarticular RF-positive also have arthritis affecting five or more joints in the first six months of disease.

However, they must also have two positive tests for rheumatoid factor, taken three months apart, which shows their immune systems are making the autoantibody associated with most cases of adult rheumatoid arthritis.

This type is less common than RF-negative, affecting between 5% and 10% of children with JIA.

Enthesitis-Related Arthritis

Children with the enthesitis-related arthritis subtype fit into one of two categories.

Some of them have symptoms where a ligament, tendon, or joint capsule attaches to bone, which is called an entheses site.

Others have pain and inflammation in either joints or enthese sites (called enthesitis) along with two or more of the following:

• Inflammation of sacroiliac joints (at the base of the spine) or pain and stiffness in the lumbosacral region in the lower back
• Positive test for HLA-B27 genetic marker
• In boys, onset after age 6
• First-degree relative with ankylosing spondylitis, enthesitis-related arthritis, inflammation of the sacroiliac joint with inflammatory bowel disease, or acute eye inflammation (acute anterior uveitis)

This type of arthritis affects 20% of children with JIA.

Systemic Arthritis

Children with systemic arthritis (also called Still's disease) have arthritis symptoms plus a fever that lasts two weeks or longer and spikes for three days or more, along with one of the following symptoms:

• Enlargement of lymph nodes
• Enlargement of liver or spleen (hepatomegaly or splenomegaly)
• Inflammation of the lining of the heart or lungs (pericarditis or pleuritis)
• Rash (non-itchy) of variable duration that may move to different parts of the body

Systemic arthritis affects 10% of children with JIA.

Psoriatic Arthritis

Children classified with the psoriatic arthritis subtype have both arthritis and psoriasis, or they are affected by arthritis and meet two of the following conditions:

• Dactylitis (sausage fingers or toes)
• Nail pitting/splitting
• A first-degree relative with psoriasis

Between 2% and 15% of children with JIA are diagnosed with this type.

Undifferentiated Arthritis

Some children have inflammation in one or more joint but don't fit neatly into one of the other categories, and these cases are called undifferentiated arthritis.

Some kids may not meet the definition of any subtype, while others may meet the definition of two or more.

A Word From Verywell

Getting proper treatment for your child with JIA depends on a doctor accurately diagnosing their subtype. If you have trouble finding a pediatric rheumatologist in your area, talk to your child's pediatrician about who would be best to see close by.

If you have to leave the area to get a reliable diagnosis, you may still be able to coordinate treatment through a local doctor.