Polymyositis

Definition

Polymyositis is an inflammatory muscle disease causing weakness and pain. Dermatomyositis is identical to polymyositis with the addition of a characteristic skin rash.

Description

Polymyositis (PM) is an inflammatory disorder in which muscle tissue becomes inflamed and deteriorates, causing weakness and pain. It is one of several types of inflammatory muscle disease, or myopathy. Others include dermatomyositis (DM) and inclusion body myositis. All three types are progressive conditions, usually beginning in adulthood. A fourth type, juvenile dermatomyositis, occurs in children. Although PM and DM can occur at any age, 60% of cases appear between the ages of 30 and 60. Females are affected twice as often as males.

Causes & symptoms

Causes

The cause of PM and DM is not known, but it is suspected that a variety of factors may play a role in the development of these diseases. PM and DM may be autoimmune diseases, caused by the immune system's attack on the body's own tissue. The reason for this attack is unknown, although some researchers believe that a combination of immune system susceptibility and an environmental trigger may explain at least some cases. Known environmental agents associated with PM and DM include infectious agents such as Toxoplasma, Borrella (Lyme disease bacterium), and coxsackievirus. Most cases, however, have no obvious triggers (direct causative agents). There may also be a genetic component in the development of PM and DM.

Symptoms

The early symptoms of PM and DM are slowly progressing muscle weakness, usually symmetrical between the two sides of the body. PM and DM affect primarily the muscles of the trunk and those closest to the trunk, while the hands, feet, and face usually are not involved. Weakness may cause difficulty walking, standing, and lifting objects. Rarely, the muscles of breathing may be affected. Weakness of the swallowing muscles can cause difficulty swallowing (dysphagia). Joint pain and/or swelling also may be present. Later in the course of these diseases, muscle wasting or shortening (contracture) may develop in the arms or legs. Heart abnormalities, including electrocardiogram (ECG) changes and arrhythmias, develop at some time during the coursed of these diseases in about 30% of patients.

Dermatomyositis is marked by a skin rash. The rash is dusky, reddish, or lilac in color, and is most often seen on the eyelids, cheeks, bridge of the nose, and knuckles, as well as on the back, upper chest, knees, and elbows. The rash often appears before the muscle weakness.

Diagnosis

PM and DM are often difficult diseases to diagnose, because they are rare, because symptoms come on slowly, and because they can be mistaken for other diseases causing muscle weakness, especially limb girdle muscular dystrophy.

Accurate diagnosis involves:

• A neurological exam.
• Blood tests to determine the level of the muscle enzyme creatine kinase, whose presence in the circulation indicates muscle damage.
• Electromyography, an electrical test of muscle function.
• Muscle biopsy, in which a small sample of affected muscle is surgically removed for microscopic analysis. A biopsy revealing muscle cells surrounded by immune system cells is a strong indicator of myositis.

Treatment

PM and DM respond to high doses of immunosuppressant drugs in most cases. The most common medication used is the corticosteroid prednisone. Prednisone therapy usually leads to improvement within two or three months, at which point the dose can be tapered to a lower level to avoid the significant side effects associated with high doses of prednisone. Unresponsive patients are often given a replacement or supplementary immunosuppressant, such as azathioprine, cyclosporine, or methotrexate. Intravenous immunoglobulin treatments may help some people who are unresponsive to other immunosuppressants.

Pain can usually be controlled with an over-the-counter analgesic, such as aspirin, ibuprofen, or naproxen. A speech-language therapist can help suggest exercises and tips to improve difficulty in swallowing. Avoidance of weight gain helps prevent overtaxing weakened muscles.

Alternative treatment

As with all autoimmune conditions, food allergies/intolerances and environemental triggers may be contributing factors. For the food allergies and intolerances, an elimination/challenge diet can be used under the supervision of a trained practitioner, naturopath, or nutritionist, to identify trigger foods. These foods can then be eliminated from the person's diet. For environmental triggers, it is helpful to identify the source so that it can be avoided or eliminated. A thorough detoxification program can help alleviate symptoms and change the course of the disease. Dietary changes from processed foods to whole foods that do not include allergen trigger foods can have significant results. Nutrient supplements, especially the antioxidants zinc, selenium, and vitamins A, C, and E, can be beneficial. Consistutional homeopathic treatment can work at a deep level to rebalance the whole person. Acupuncture and Chinese herbs can be effective in symptom alleviation and deep healing. Visualization, guided imagery, and hypnosis for pain management are also useful.

Prognosis

The progression of PM and DM varies considerably from person to person. Immunosuppressants can improve strength, although not all patients respond, and relapses may occur. PM and DM can lead to increasing weakness and disability, although the lifespan usually is not significantly affected. About half of the patients recover and can discontinue treatment within five years of the onset of their symptoms. About 20% still have active disease requiring ongoing treatment after five years, and about 30% have inactive disease but some remaining muscle weakness.

Prevention

There is no known way to prevent myositis, except to avoid exposure to those environmental agents that may be associated with some cases.

Key Terms

Autoimmune disease

A diseases in which the body's immune system, responsible for fighting off foreign invaders such as bacteria and viruses, begins to attack and damage a part of the body as if it were foreign.

Immunosuppressant

A drug that reduces the body's natural immunity by suppressing the natural functioning of the immune system.

Further Reading

For Your Information

Books

• Thoene, Jess G., ed. Physicians' Guide to Rare Diseases. 2nd ed. Montvale, NJ: Dowden Publishing Co., 1995.

  Periodicals

• Masteglia, Frank L., Beverley A. Phillipos, and Paul Zilko. "Treatment of Inflammatory Myopathies." Muscle & Nerve 20 (June, 1997): 651+.
• Plotz, Paul H., et al. "Myositis: Immunologic Contributions to Understanding Cause, Pathogenesis, and Therapy."Annals of Internal Medicine 122 (1995): 715-724.

  Organizations

• Dermatomyositis and Polymyositis Support Group. 146 Newtown Road, Southampton, SO2 9HR, U.K.
• Muscular Dystrophy Association. 3300 East Sunrise Drive, Tucson, AZ 85718. (520) 529-2000, (800) 572-1717. http://www.mdausa.org
• Myositis Association of America. 600-D University Boulevard, Harrisonburg, VA 22801. (540) 433-7686. http://www.myositis.org
• National Institutes of Health. National Institute of Arthritis and Musculoskeletal and Skin Diseases. 900 Rockville Pike, Bethesda, MD 20892. (301) 496-8188. http://www.hih.gov.niams/

Gale Encyclopedia of Medicine. Gale Research, 1999.