Definition

Polymyositis is a disease of the muscles. It usually affects the muscles closest to the trunk of the body. However, it may affect muscles anywhere in the body. The muscles become inflamed or swollen. This causes pain. The disease is progressive and starts slowly. If untreated, the muscles gradually become weaker. The pain in the muscles also increases.

Front Muscles of Trunk Copyright © Nucleus Medical Media, Inc.

This rare disease is believed to be an autoimmune disorder. Your immune system is your body’s defense system. It fights diseases and infections. In this case your immune system attacks your own muscle tissue by mistake.

The sooner the disease is treated, the better the outcome. If you suspect you have this condition, contact your doctor.

Causes

The cause is unknown. Factors that may contribute to polymyositis include:

• Genetics
• A virus that sets off the condition
• A reaction to certain drugs that set off the condition

Risk Factors    TOP

The following factors increase your chance of developing polymyositis:

• Age: 50-70 years old
• Gender: Women are more likely to develop polymyositis than men.

Symptoms    TOP

Symptoms include:

• General weakness (lethargy)
• Weakness in the muscles of the hips and shoulders—occurs slowly and gradually over a period of weeks or even months
  • This gradual muscle weakness is often the first sign of the disease
• Achy, tender muscles
• Weight loss
• Fatigue after standing or walking
• Trouble rising from a chair
• Great effort needed to climb stairs
• Struggle to lift objects
• Difficulty reaching overhead (eg, unable to comb your hair)
• Trouble with swallowing (when muscles in the front of the neck and throat become involved)—rare
• Difficulty breathing (if it affects the lungs or chest muscles)—rare

Diagnosis    TOP

This diagnosis is not easy. Symptoms vary from person to person. It is often a matter of ruling out other diseases and conditions. Your doctor will ask about your symptoms and medical history. A physical exam will be done.

Tests may include the following:

• Blood test—to check for autoantibodies (antibodies that attack parts of your body)
• Creatine kinase test—blood test that looks for elevated levels of muscle proteins or enzymes called creatine kinase (CK) (when a muscle is damaged, CK is released into the bloodstream)
• Aldolase test—a blood test that looks for elevated levels of aldolase (a substance released into the bloodstream when a muscle is damaged)
• Electromyogram (EMG) —measures activity of your muscles, often used to help find causes of muscle weakness or damage
• Muscle biopsy —a small piece of muscle tissue is removed and examined to see if the muscle is damaged in some way
• Magnetic resonance imaging (MRI) —noninvasive scan, using magnetic waves, of your muscles to see if any muscles are inflamed

Treatment    TOP

While there is no cure, treatment can improve your muscle strength and function. Talk with your doctor about the best plan for you. Options include:

Prevention    TOP

There are no known ways to prevent polymyositis.