Juvenile Polymyositis

Juvenile polymyositis (JPM) is an autoimmune disease that causes inflammation of the muscles (myositis) in children. In autoimmune diseases, the immune system mistakenly attacks healthy tissue and cells. For children with JPM, this results in muscle weakness which, in severe cases, can affect systems of the body such as the digestive tract, heart, and lungs.

JPM is rare in children. It generally develops in early adolescence, and the condition is more common in girls.

Both JPM and the more common juvenile dermatomyositis are forms of the autoimmune inflammatory muscle disorder, myositis.

What are the symptoms of juvenile polymyositis?

The most common symptom of JPM is muscle weakness. A gradually progressing muscle weakness that occurs in the muscles of the hips, thighs, shoulders, upper arms, and neck. It affects both sides of the body at the same time and can make simple movements difficult, such as getting up out of a chair or out of bed.

A more severe form of this condition may cause:

• Shortness of breath
• Difficulty swallowing
• Voice changes
• Calcium deposits in the muscles
• Fever
• Weight loss

How is juvenile polymyositis diagnosed?

If you or your pediatrician suspect JPM, your child will be referred to a pediatric rheumatologist, who will conduct a full medical exam and schedule some tests. Tests used to diagnose JPM include:

• Blood and urine tests check for elevated muscle-related enzymes.
• Magnetic resonance imaging (MRI) gives a view of the muscles that can show inflammation or can guide a muscle biopsy.
• Muscle biopsy allows for a close look of muscle tissue under a microscope, which can indicate the extent of tissue and muscle damage due to inflammation and distinguish JPM from other muscle-related diseases.

How is juvenile polymyositis treated?

JPM is treated primarily with medication and physical therapy. Specialists in our Pediatric Rheumatology Program will work with you to create the right treatment plan for your child.

Medications that your physician may prescribe to treat JPM include corticosteroids, methotrexate, mycophenolate, rituximab, and intravenous immune globulin.

Physical therapy and physical activity is essential for children with this condition to maintain and increase muscle strength and flexibility.

Muscle weakness due to JPM can affect chewing and swallowing. Your child may be scheduled for appointments with a dietician to discuss healthy, safe eating.