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Polymyositis by Diane Safer, PhD

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

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

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

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

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

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:

Medication

There are a number of medicines that may be prescribed. Corticosteroids (eg, prednisone ) are usually one of the first treatments that are tried. These medicines work by suppressing the immune system, which reduces inflammation. In some cases, it may take 3-6 months to have an improvement in symptoms.

Other medicines that may be recommended instead of prednisone include:

Methotrexate (eg, Rheumatrex, Trexall)
Azathioprine (eg, Azasan, Imuran)
Other drugs to suppress the immune system, such as cyclosporine (eg, Gengraf, Neoral, Restasis), chlorambucil (eg, Leukeran)

Intravenous immunoglobulin is another treatment option that involves using an IV needle to inject extra immunoglobins (special proteins) into the body. This process may help the immune system function better and reduce inflammation.

In severe cases of polymyositis, the doctor may recommend investigational drugs, such as:

Rituximab (Rituxan)
Tumor necrosis factor (TNF) inhibitors (eg, etanercept [Enbrel], infliximab [Remicade])

Physical Therapy

Your doctor may recommend that you work with a physical therapist to prevent permanent muscle damage. Exercise may include:

A regular stretching routine for weakened arms and legs
Light strengthening as the pain lessens and function returns

Dietary Changes

Polymyositis can lead to problems with chewing and swallowing. By working with a registered dietician, you can learn ways to adjust to these changes and get the nutrition that you need.

Speech Therapy

Polymyositis may also cause speech problems. A speech therapist can assess your condition and create a program for you.

Prevention

There are no known ways to prevent polymyositis.

RESOURCES:

American Autoimmune Related Diseases Association http://www.aarda.org/
The Myositis Association http://www.myositis.org/

CANADIAN RESOURCES:

The Arthritis Society http://www.arthritis.ca/
Health Canada http://www.hc-sc.gc.ca/index_e.html/

References:

American Academy of Orthopaedic Surgeons. Myositis. American Academy of Orthopaedic Surgeons website. Available at: http://orthoinfo.aaos.org/topic.cfm?topic=A00198&return_link=0 . Updated July 2007. Accessed November 10, 2010.
Choy EH, Hoogendijk JE, Lecky B, Winer JB, Gordon P. Immunosuppressant and immunomodulatory treatment for dermatomyositis and polymyositis. Cochrane Database Syst Rev. 2009;(4):CD003643.
Idiopathic inflammatory myopathy: treatment. EBSCO DynaMed website. Available at: http://www.ebscohost.com/dynamed/ . Updated September 2, 2011. Accessed September 28, 2011.
Myositis Association. Getting diagnosed. The Myositis Association website. Available at: http://www.myositis.org/learn-about-myositis/diagnosis . Accessed September 12, 2005.
Myositis Association. Myositis FAQ. Myositis Association website. Available at: http://www.myositis.org/learn-about-myositis/types-of-myositis. Accessed September 12, 2005.
Myositis Association. Treatment. Myositis Association website. Available at: http://www.myositis.org/learn-about-myositis/treatment. Accessed September 12, 2005.
National Institute of Neurological Disorders and Stroke. Polymyositis information page. National Institute of Neurological Disorders and Stroke website. Available at: http://www.ninds.nih.gov/disorders/polymyositis/polymyositis_pr.htm . Accessed September 12, 2005.
Polymyositis. The Mayo Clinic website. Available at: http://www.mayoclinic.com/health/polymyositis/DS00334/DSECTION=treatments-and-drugs . Updated July 7, 2011. Accessed September 28, 2011.
Simply stated: the creatine kinase test. Quest. 2000;7(1).

Last reviewed [Under Medical Review] by Rosalyn Carson-DeWitt, MD

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