What Is Polyarticular Juvenile Idiopathic Arthritis?

Polyarticular juvenile idiopathic arthritis is a type of juvenile idiopathic arthritis (JIA). JIA is a group of disorders that causes arthritis (stiff, swollen, painful joints) in children.

Children with polyarticular (pol-ee-ar-TIK-yuh-lur) juvenile idiopathic arthritis (polyarticular JIA) have arthritis in five or more joints during the first 6 months of illness.

Treatments can help with symptoms, so children can live a full and active life. The symptoms can go away for a time (called remission). In some kids, the condition goes away permanently.

What Are the Signs & Symptoms of Polyarticular Juvenile Idiopathic Arthritis?

Children with polyarticular arthritis may start out with arthritis in only one or two joints, and then increase to more than five. Or they may get arthritis in many joints all at once.

Other problems that can happen include:

• anemia (low red blood cell count)
• an enlarged liver, spleen, or lymph nodes
• joint damage
• inflammation of the lining of the heart or lungs

What Causes Polyarticular Juvenile Idiopathic Arthritis?

Polyarticular JIA is an autoimmune disease. This means that the body’s immune system, which normally attacks germs, mistakenly attacks the joints. This causes inflammation (swelling and irritation) in the joints and other problems.

Polyarticular JIA usually starts when kids are 1–3 years old, or 10–14 years old. It happens more often in girls than boys.

Doctors don’t know exactly why kids and teens get JIA. “Idiopathic” means “from an unknown cause.” It can run in families but often does not. It’s likely due to a combination of:

• genetic (inherited) causes
• the way the immune system responds to infection and illness
• a trigger, such as an infection

How Is Polyarticular Juvenile Idiopathic Arthritis Diagnosed?

To diagnose polyarticular JIA, doctors:

• ask about symptoms
• do an exam
• ask whether other family members have had similar problems
• do X-rays or other imaging studies to look inside the joints
• order blood tests to check for:
  • anemia or other blood problems
  • inflammation in the body
  • markers for some types of arthritis or autoimmune illnesses

Sometimes, an orthopedic surgeon (bone doctor) takes samples of joint fluid or synovium (the lining of the joints). The sample is sent to a lab for testing.

How Is Polyarticular Juvenile Idiopathic Arthritis Treated?

Polyarticular JIA is treated by a care team that includes:

• a  (for problems with joints and connective tissue)
• a primary care doctor (such as a pediatrician or family medicine doctor)
• a physical therapist

Treatment goals are to ease pain and inflammation, improve strength and flexibility, and prevent joint damage. Treatment usually includes medicines to ease inflammation and physical therapy.

Sometimes surgery is needed for damaged joints.

How Can Parents Help?

Polyarticular JIA usually is a lifelong disease, but treatments can help ease pain, keep kids active, and prevent long-term joint damage. To help your child:

• Be sure your child takes all medicines exactly as directed.
• Work with the physical therapist to develop a regular exercise program. This will help keep your child’s muscles strong and flexible. 
• Learn all you can about polyarticular JIA with your child. Your care team is a great resource. You also can find information and support online at:
  • The Arthritis Foundation