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Polymyositis is an inflammatory muscle disease that causes weakness and pain. The condition primarily affects the muscles of the trunk (such as shoulder and hip muscles) and those close to the trunk (upper arms, thighs and neck). The hands, feet and face are usually not involved.
Polymyositis is one of several different types of inflammatory muscle diseases (myopathies). Other types include dermatomyositis and inclusion body myositis.
The cause of polymyositis is unknown. It is suspected that a number of factors play a role in the development of the condition. It is thought that polymyositis may be an autoimmune disease, caused by the body’s natural immune defence 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. However, about 60% of cases occur between the ages of 30 and 60 years. Females are approximately twice as likely as men to develop polymyositis.
Signs and Symptoms
The onset of symptoms in polymyositis usually occurs gradually. The 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. Other symptoms of this disorder may include:
- Aching, tender muscles
- Weight loss.
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 chest muscles involved with breathing can also be affected but this is rare. Disturbances of the heart rhythm may also be experienced.
Approximately one third of people with polymyositis experience pain in the joints. Swelling, fluid and other forms of non-deforming arthritis may also accompany the pain. These rheumatic symptoms are usually mild and respond well to medication.
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 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.
A test which measures the electrical patterns of the muscles (electromyography) may also be performed.
Sometimes a tissue sample (biopsy) is taken from affected muscles. This sample is sent to a laboratory for further investigation. Characteristic changes in the muscle tissue can be a strong indicator of polymyositis.
An electrocardiograph (ECG) to trace the heart’s electrical activity may be taken and a magnetic resonance imaging (MRI) scan may also be performed.
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 defences against infections and foreign bodies (immunosuppressants) may also be prescribed. Non steroidal anti-inflammatory medications (NSAID's) such as voltaren may be recommended to treat any pain and discomfort.
Corticosteroid treatment may take two to three months to produce significant improvement in symptoms. Once symptoms improve the medication doses are reduced. The doctor, in conjunction with a physiotherapist and/or occupational therapist, may also recommend a specific exercise programme to 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. Approximately 50% of those affected recover and are able to discontinue treatment within five years of the onset of symptoms. Another 20% will have active disease needing treatment for longer than five years. And the remaining 30% will not have active disease after five years, but they will have some remaining muscle weakness.
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.
Muscular Dystrophy Association of NZ Inc.
PO Box 16 238
Ph: 09 815 0247
Fax: 09 815 7260
Freephone: 0800 800 337 (outside Auckland only)
National Institute of Neurological Disorders (2007) Polymyositis. National Institutes of Health. http://www.ninds.nih.gov/disorders/polymyositis/polymyositis.htm
Robinson, R. (2006) Polymyositis. The Gale Encyclopaedia of Medicine, Third Edition. Jacqueline L. Longe, Editor. Farmington Hills, MI. Thomson Gale.
Shiel, W. C. (2006) Polymyositis and Dermatomyositis. MedicineNet, Inc. http://www.medicinenet.com/script/main/art.asp?articlekey=454&pf=3&page=1
Last Reviewed – 5/12/07