Dermatomyositis

Dermatomyositis 

Definition

Dermatomyositis (DM) is a rare inflammatory muscle disease that leads to destruction of muscle tissue usually accompanied by pain and weakness.

Description

Dermatomyositis is one of a group of three related diseases called inflammatory myopathies. The other two are polymyositis and inclusion-body myositis. These diseases are rare; only about 20,000 people in the United States have dermatomyositis. Another estimates suggest that DM occurs in about 5.5 individuals out of every one million. The disease is of unknown origin and can develop in children and adults. Most often individuals either develop DM either between the ages of five and 14 or they do not develop it until they are over age 45. In all age groups, females are twice as likely to develop the disease than males. Although DM causes pain and weakness, it is not necessarily life threatening. However, adults, but not children, who develop DM have an increased risk of developing cancer and should be screened for malignancies regularly.

Causes and symptoms

The exact cause of dermatomyositis is unknown. It is an autoimmune disease. In a healthy body, cells of immune system attack only foreign or defective cells in the body to protect it from disease. In an autoimmune disease, the immune system attacks normal body cells. In the case of DM, immune system cells attack healthy cells of small blood vessels in the muscle and skin. Over time, this causes muscle fiber to shrink and sometimes cuts off blood supply to the muscle. DM tends to develop in muscles closest to the center of the body.

As yet, there is no clear explanation of what causes an individual to develop DM. It is thought that the disease may be triggered by a virus or exposure to certain drugs or vaccines. According to the Muscular Dystrophy Association, recent research suggests developing DM may be related to the mixing of blood cells that sometimes occurs between the mother and fetus during pregnancy. The disease is not directly inherited, although there may be some genetic sensitivity toward whatever triggers it.

Often the first sign of DM is the development of a patchy, scaly, violet to dark red skin rash on the face, neck, shoulders, upper chest, knees, or back. Often the rash appears before any signs of illness or muscle weakness. About 40% of children and teens develop hard, painful bumps under the skin that are deposits of calcium, a mineral used in bone formation. This condition, called calcinosis, is much less common in adults.

Muscle weakness, especially in the upper arms, hips, thighs, and neck, becomes apparent in activities such as climbing stairs or reaching up over the head. This weakness develops after the rash appears. Some people have difficulty swallowing and chewing when the muscles of the face and esophagus are affected. Individuals may also feel tried, weak, have a low-grade fever, weight loss, and joint stiffness. Some individuals have the rash for years before they progress to these symptoms, while in others the onset of symptoms is rapid. In children the development of symptoms is almost always gradual, making diagnosis especially difficult.

Diagnosis

DM can be difficult to diagnose, and often the first doctor an individual sees is a dermatologist for treatment of the rash and then is referred to a rheumatologist, specialist in internal medicine or neurologist when DM is suspected. Many tests may be done to rule out other diseases before a firm diagnosis is made. A blood test is done to measure the level of creatine kinase. Creatine kinase is an enzyme found in muscle tissue. When muscle is damaged, this enzyme leaks out into the blood. An increased level of creatine kinase in the blood suggests DM as a possible diagnosis. Another blood test may be done to test for specific immune system antibodies. Antibodies are proteins made in response to material the body thinks is foreign.

An electromyogram (EMG) is a test that measures electrical activity in muscles as they contract. Individuals with inflammatory myopathies usually have distinct patterns of electrical activity in the affected muscles. However, up to 15% of people with DM have normal electromyogram readings, so this test is not definitive. The definitive test is a muscle biopsy. The doctor takes a small sample of muscle tissue and examines it under a microscope. From this sample, the doctor can differentiate DM from other inflammatory myopathies and other muscle wasting diseases.

Treatment

The goal of treatment is to improve muscle strength and allow the individual to participate in normal daily activities. Individuals are given steroid drugs (prednisone, corticosteroids) that suppress the immune system. Over time, these drugs often produce undesirable side effects, so treatment is usually begun with a large dose, then tapered to the minimum dose needed for maintenance. People who do not respond well to steroid treatment may be treated with other immunosuppressive drugs or intravenous immunoglobulin. Individuals with DM are advised to avoid exposure to the sun, as sunlight worsens the skin rash. Physical therapy is often helpful in keeping joints from stiffening and freezing. Moderate exercise is also recommended.

Alternative treatment

A healthy diet high is recommended for all individuals with supplemental protein for those with severe muscle damage.

Prognosis

The course of DM is highly variable. In about 20% of people, the disease spontaneously goes into remission and individuals are able to lead symptom-free lives for long periods. On the other hand, in about 5% of individuals the disease progresses to death because of heart and lung involvement. The majority of people continue to have some symptoms and require long-term treatment, but their degree of daily activity varies greatly.

Serious complications from DM include involvement of the muscles of the heart and lungs, difficulty eating and swallowing, and a tendency to develop cancer. This association is seen only in adults and not in children. Individuals over age 60 are more likely to have serious complications than younger individuals.

Prevention

There is no known way to prevent this disease.

Resources

Periodicals

Koler, Ric A. and Andrew Montemarano. "Dermatomyositis." American Family Physician, 24, no. 9 (1 November 2001) 1565–1574 [cited 16 February 2005]. 〈http://www.aafp.org/afp/2001101/1565.html〉.

Organizations

American Autoimmune Related Disease Association. 22100 Gratiot Avenue, Eastpointe, East Detroit, MI 48201-2227. 800-598-4668. http://www.aarda.org.

Muscular Dystrophy Association. 3300 East Sunrise Drive, Tucson, AZ 85718-3208. 800-572-1717. http://www.mdausa.org

Myositis Association. 1233 20th Street, NW, Washington, DC 20036. 800-821-7356. http://www.myositis.org.

National Organization for Rare Disorders (NORD). P. O. Box 1968, Danbury, CT 06813-1968. 800-999-NORD. http://www.rarediseases.org.

Other

Callen, Jeffrey P. Dermatomyositis, 5 December 2002 [cited 16 February 2005]. http://www.emedicine.com/derm/topic98.htm.

Hashmat, Aamir and Zaineb Daud. Dermatomyositis/Polymyositis, 16 January 2004 [cited 16 February 2005]. http://www.emedicine.com/neuro/topic85.htm.

Key terms

Immunoglobulin — Material containing specific antibodies to fight disease that can be injected into an individual to fight infection.

Inflammation — An infection or irritation of a tissue.

Myopathy — Relating to muscle tissue.

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dermatomyositis /der·ma·to·myo·si·tis/ (-mi?o-si´tis) a collagen disease marked by nonsuppurative inflammation of the skin, subcutaneous tissue, and muscles, with necrosis of muscle fibers.

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der·ma·to·my·o·si·tis (dûrm-t-m-sts)

n.

A progressive inflammatory condition characterized by muscular weakness, a skin rash, and edema of the eyelids and periorbital tissue.

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dermatomyositis (dur´mtōmī´-ōsī´tis),

n (polymyositis, dermatomucosomyositis) a form of collagen disease related to scleroderma and lupus erythematosus. The skin lesions are diffuse erythematous desquamations or rashlike lesions. The skin symptoms are related to a variety of patterns of myositis.

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dermatomyositis

an acute, subacute or chronic disease of humans, marked by nonsuppurative inflammation of the skin, subcutaneous tissue and muscles, with necrosis of muscle fibers.

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canine familial dermatomyositis

an inherited disease found mainly in Collies and Shetland sheepdogs. Starting at a young age, there is hair loss, alopecia, scaling, crusting and sometimes ulceration on the face, ear tips, pressure areas over the carpus and tarsus, and the tail. Myositis may be severe, causing a stiff gait, difficulty in chewing and atrophy, or be unrecognized except by biopsy.