Subtypes of Juvenile Idiopathic Arthritis

Juvenile idiopathic arthritis (JIA) is an umbrella term for autoimmune or autoinflammatory types of arthritis in children under 16 years old. This disease used to be called juvenile rheumatoid arthritis (JRA), but the name fell out of favor because it was considered misleading. JIA is not a juvenile form of adult rheumatoid arthritis. Rather, it's a form of arthritis of unknown cause in young people.

The International League of Associations for Rheumatology (ILAR) has divided juvenile idiopathic arthritis into seven subtypes:

• Oligoarthritis
• Polyarticular RF-negative arthritis
• Enthesitis-related arthritis
• Systemic arthritis
• Psoriatic arthritis
• Undifferentiated arthritis

This was primarily done for research purposes and may change again as researchers learn more about the genetics behind and course of JIA.

Oligoarthritis

Oligoarthritis is the most common form of JIA. Onset typically occurs between the ages of 1 and 6. It accounts for between 50% and 60% of JIA cases and has the best prognosis.

These kids have arthritis affecting one to four joints within the first six months of disease. Thereafter, their diagnosis is refined based on what joints are still effected:

• If a child continues having symptoms in four or fewer joints, they have persistent oligoarthritis.
• If their pain spreads to more joints down the road, they are considered to have extended oligoarthritis.

Polyarticular RF-Negative

Rheumatoid factor (RF) is an autoantibody, a protein created by the immune system that attacks and destroys a healthy part of the body as if it were a virus or other pathogen. Specifically, RF attacks the lining of the joints.

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

1. Arthritis is in five or more joints (poly means many; articular means related to the joints)
2. This occurs in the first six months of the disease
3. RF blood test is negative

This type of arthritis affects between 15% and 20% of children with JIA. Onset is typically before age 6.

Polyarticular RF-Positive

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

However, in terms of diagnostic criteria, they must also have two positive tests for rheumatoid factor, taken three months apart. This shows the immune system is making the autoantibody associated with most cases of adult rheumatoid arthritis.

This type is less common than RF-negative, affecting between 2% and 15% of children with JIA. Onset is most common between the ages of 7 and 10.

Enthesitis-Related Arthritis

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

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

Others have pain and inflammation in either joints or entheses sites 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. It typically starts after age 6 with onset being most common between the ages of 10 and 12.

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 between 5% and 15% of children with JIA. It can begin at any age.

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 3% and 10% of children with JIA are diagnosed with this type. While onset is most common in kids 2 to 3 years of age, it can begin throughout adolescence.

Undifferentiated Arthritis

Some children have inflammation in one or more joint but don't fit neatly into one of the other JIA categories. These cases are referred to as undifferentiated arthritis.

Some kids with this diagnosis may not meet the definition of any subtype, while others may meet the definition of two or more. Between 10% and 20% of JIA diagnoses fall under this category.

A Word From Verywell

Proper treatment for JIA depends on a doctor accurately diagnosing your child's 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.

You might also consider using The American College of Rheumatology’s online directory to search practitioners by zip code (choose "pediatrics" as the primary discipline).

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