Polyarticular JIA occurs when children under 16 years old develop arthritis in five or more joints. Treatment can lead to remission, but some people experience symptoms into adulthood.

Juvenile idiopathic arthritis (JIA) is a group of chronic inflammatory arthritis disorders that can occur in children. Polyarticular disease is a subtype of JIA. “Polyarticular” means “many joints.”

JIA is the most common autoimmune disease in children. In Western countries, up to about one-third of children with JIA have the polyarticular subtype. In other parts of the world, polyarticular JIA is the most common form of the disease.

JIA is a chronic disease. Over time, symptoms may persist, change, or decrease. Early treatment can help minimize symptoms, reduce long-term joint damage, and improve the quality of life for children with polyarticular JIA.

Rheumatoid factor and polyarticular JIA

Doctors classify polyarticular JIA into two subtypes, depending on whether the child’s blood consistently tests positive rheumatoid factor (RF). RF is an antibody that contributes to chronic inflammation.

RF-positive polyarticular JIA is less common but tends to be more severe.

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To receive a JIA diagnosis, you must have chronic inflammatory arthritis for at least 6 weeks. Symptoms must begin before your 16th birthday.

Polyarticular JIA causes inflammatory arthritis in both small and large joints. It often affects your hands and wrists. Affected joints are often:

  • swollen
  • painful
  • discolored
  • stiff

Children with polyarticular JIA develop arthritis in five or more joints within the first 6 months of illness.

People with polyarticular JIA must not have hallmark symptoms of the other distinct forms of JIA, such as psoriasis, enthesitis, or signs of systemic disease like persistent fever and rash. These symptoms could mean you have a different form of JIA.

Up to 10% of children with polyarticular JIA will also develop uveitis, a painful eye condition that causes redness and blurring and can lead to vision loss if left untreated. If your child receives a JIA diagnosis, their doctor will refer them for regular eye exams and advise you to monitor them closely for these symptoms.

Types of juvenile idiopathic arthritis

There are seven distinct types of JIA. In addition to the two types of polyarticular JIA, the types are:

  • Systemic JIA: arthritis and full-body symptoms such as fever, rash, serositis, and enlargement of your lymph nodes, liver, or spleen
  • Oligoarticular JIA: arthritis in four or fewer joints within the first 6 months
  • Psoriatic JIA: arthritis and a personal or family history of psoriasis, often with nail changes or dactylitis
  • Enthesitis-related JIA: arthritis and/or enthesitis in males younger than 6 years old
  • Undifferentiated JIA: arthritis that doesn’t fit any category above or meets criteria for multiple categories
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JIA is an autoimmune disorder, which means your immune system is mistakenly triggered to begin attacking your body.

In JIA, your immune system attacks your joints. This causes inflammatory arthritis with pain, discoloration, swelling, and stiffness.

Doctors aren’t yet sure what causes your immune system to misfire and begin inflaming your joints. They suspect that the cause involves a combination of genetic risk factors, infections, and other environmental triggers.

Overall, JIA is the most common autoimmune disease of childhood, with an estimated prevalence of about 1 per 1,000 U.S. children. Up to about one-third of these children have polyarticular JIA.

Although it occurs in all populations, JIA is more common in children of European heritage. Compared with other types of JIA, the polyarticular subtype is less frequent in children of East Asian descent, but it is the most prevalent type in Africa, India, and parts of the Middle East.

About 15% of children with polyarticular JIA are RF-positive. They tend to be females ages 10–13 years.

RF-negative polyarticular JIA has two peak age ranges of incidence: ages 1–3 years and 9–14 years.

Both forms are much more common in females. This is especially true for RF-positive disease.

Your child’s doctor will discuss your child’s symptoms and your family’s medical history, perform a physical exam, and order blood tests to check for inflammation and the presence of specific antibodies.

Imaging tests such as X-rays, ultrasounds, and MRIs may also be helpful.

To help treat and diagnose JIA, your child may need to see specialists such as a:

Your doctor might recommend the following treatments for polyarticular JIA:

JIA is a chronic condition with no known cure. But symptoms may come and go, and disease remission is possible.

A 2017 review found that up to 7% of children with JIA had entered remission 18 months after diagnosis. That percentage increased to around 40% after 10 or more years.

A 2016 survey of 176 people with JIA found that 30 years after diagnosis, 59% of participants were in clinical remission and off medication. Those with RF-positive polyarticular JIA appeared less likely to enter remission.

But these remission rates may now be underestimates, considering recent advances in treatment. When started promptly, disease-modifying treatments can help manage JIA symptoms, reduce joint inflammation and long-term damage, and increase your chances of remission.

However, even with appropriate therapy, some people with JIA experience chronic pain and disability from arthritis, according to a 2020 Canadian study with 247 participants.

RF-positive polyarticular JIA, in particular, appears more likely to persist. A small percentage of people with JIA will go on to need joint replacement surgery, even after aggressive treatment.

What is the most common type of juvenile idiopathic arthritis?

In the United States and western Europe, oligoarticular JIA is the most common form of JIA. Children with oligoarticular JIA have arthritis in fewer than five joints.

At what age does polyarticular juvenile idiopathic arthritis occur?

By definition, all forms of JIA begin before 16 years of age.

RF-negative polyarticular JIA has two peak age ranges of incidence: ages 1–3 years and 9–14 years.

In contrast, RF-positive polyarticular JIA is more common in older children (ages 10–13 years).

What is the difference between polyarticular juvenile idiopathic arthritis and rheumatoid arthritis?

Rheumatoid arthritis is diagnosed in adulthood, usually in middle-aged females. It affects the small and large joints, as well as other body systems such as your heart, lungs, blood, and skin. Most people with RA test positive for RF, and most will have the disease all their life.

Polyarticular JIA occurs in children less than 16 years old. Apart from causing occasional uveitis, it usually doesn’t affect other organ systems. Some children with polyarticular JIA will test positive for RF, but most will not. Children with JIA have a significant chance of entering remission in their lifetime.

Polyarticular JIA falls under the umbrella of JIA, a group of chronic inflammatory arthritis disorders diagnosed in childhood. Children with polyarticular JIA develop inflammatory arthritis that affects five or more joints within the first 6 months of disease.

Over time, their arthritis may persist or subside. Sometimes, it evolves to affect more joints and include additional symptoms.

Polyarticular JIA can be RF-positive or RF-negative. RF-positive polyarticular JIA is more common in teenage females and appears more challenging to force into remission.

Although JIA is a chronic disease, the outlook continues to improve with newer treatments. Prompt diagnosis and early use of DMARDs can improve quality of life and reduce joint damage and future disability. Many children with a JIA diagnosis will eventually enter remission and may even be able to stop taking medication.