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Polymyositis - symptoms, diagnosis, treatment

Polymyositis is an inflammatory disease that causes muscle weakness primarily affectings the shoulders, upper arms, pelvis and thighs. The hands, feet and face are not usually affected.

The cause of polymyositis is unknown. It is suspected that a number of factors play a role in the development of the condition's symptoms. It is thought that polymyositis may be an autoimmune disease, caused by the body’s natural immune defense mechanisms attacking its own tissue (autoimmune reaction). Viruses are also suspected of playing a role in its development, and there may be a genetic component to the condition.   Polymyositis can occur at any time of life, althought it is uncommon under the age of 18 years and about 60% of cases occur between the ages of 30 and 60 years.  Women are more commonly affected by the condition than men. 

Polymyositis is one of several different types of inflammatory muscle diseases (myopathies). Other types include dermatomyositis and inclusion body myositis.

Signs and symptoms 

The onset of symptoms usually occurs gradually over a period of months. Occasionally, however, symptoms can develop rapidly over a period of days. Symptoms may also come and go for no apparent reason. The main symptom associated with polymyositis is muscle weakness. The muscle weakness usually first occurs in the hip and shoulder areas and is slowly progressive. The weakness is usually painless but sometimes aching, discomfort, or mild tenderness of the affected muscles is experienced.

As the condition progresses the muscles affected become wasted. Eventually people may have difficulty walking, standing, climbing stairs and lifting things. Their neck and throat muscles may also be affected, making it difficult for them to swallow and changing their voice. The muscles involved with breathing (including the diaphragm) may be affected in severe cases.  In rare cases the lungs and heart may be affected leading to symptoms such as heart rhythm disturbances. 


Because polymyositis is a rare disease and its symptoms can be mistaken for other conditions, it can be difficult to diagnose.  In order for an accurate diagnosis to be made a referral to a neurologist or musculoskeletal specialist may be recommended. The doctor will perform a physical and neurological examination and will assess the history and nature of the symptoms. Blood tests may be taken to determine if certain muscle enzymes (creatine kinase) and antibodies (rheumatoid factor) are present.

Two tests most commonly performed to provide a definitive diagnosis are an electromyogram (EMG) and a muscle biopsy:

  • An EMG measures the electrical activity in the muscles. The pattern of the electrical activity in the muscles can demonstrate if the muscle weakness is due to polymyositis.
  • A biopsy is where a sample of muscle tissue is collected during a minor surgical procedure under a local anesthetic. The muscle tissue sample is sent to a laboratory for further investigation. Characteristic changes in the muscle tissue can be a strong indicator of polymyositis.
Other tests that may also be performed include an electrocardiograph (ECG) to trace the heart’s electrical activity may be taken and a magnetic resonance imaging (MRI).


The main treatment for polymyositis is medication. Corticosteroid medications such as prednisone are most commonly used. These are usually given in high doses and have a powerful anti-inflammatory effect. Medications that counteract the body’s defenses against infections and foreign bodies (immunosuppressants) are often used in combination with the corticosteroids. Examples of immunosuppressive medications include azathioprine and cyclosporine. Non-steroidal anti-inflammatory medications (NSAID's) such as diclofenac may be recommended to treat any pain and discomfort.

Treatment may take two to three months to produce significant improvement in symptoms. Once symptoms improve the medication doses may be reduced.  Physical therapy and exercise, in conjunction with a physiotherapist and/or occupational therapist, is important to maintain muscle and joint movement and help restore muscle strength.  Alternative treatments such as nutritional supplements, elimination diets, homeopathy and acupuncture may help to relieve symptoms in some people.

The course of the disease varies from person to person. Most people affected will improve, however not all will make a full recovery. Those who experience severe symptoms that do not respond adequately to treatment may be left with significant disability.

Further information and support

The Muscular Dystrophy Association of New Zealand aims to improve the quality of life for all people with neuromuscular conditions and their families:

PO Box 12063
Auckland, 1642
Ph: 0800 800 337 or (09) 815 0247
Fax (09) 815 7260



Muscular Dystrophy Association of New Zealand Inc (2010) Polymyositis and Dermatomyositis. Fact Sheet. Muscular Dystrophy Association of New Zealand Inc. Auckland
National Institute of Neurological Disorders (2011) Polymyositis. National Institutes of Health.
Robinson, R. (2006) Polymyositis. The Gale Encyclopaedia of Medicine, Third Edition. Jacqueline L. Longe, Editor. Farmington Hills, MI. Thomson Gale.
Shiel, W. C. (2013) Polymyositis and Dermatomyositis. MedicineNet, Inc.

Last Reviewed – 20 August 2013
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