Dermatomyositis and Polymyositis

Definition

Dermatomyositis and polymyositis are connective tissue diseases in which there is muscle weakness and tenderness. The two disorders are very similar, except that dermatomyositis involves the skin as well as the muscles, while polymyositis involves only the muscles.

Description

The major manifestation of polymyositis is inflammation leading to destruction of muscle and increasing muscular weakness. As the disease progresses, muscle tissue is replaced by functionless scar tissue. Both have features in common with rhematoid arthritis, lupus, and progressive systemic sclerosis (scleroderma).

Causes and Risk Factors

The causes of dermatomyositis and polymyositis are unknown. It appears that abnormal immunological factors are responsible for at least part of inflammatory attack against muscle tissue. The symptoms of muscular weakness usually wax and wane, but in some instances, the disease may progress rapidly.

The disease may affect persons of any age, but the peak incidence is in the fifth and sixth decades of life. Women are affected twice as commonly as men.

Symptoms

Muscle of the shoulder, arms, pelvis, and thighs are the most frequent targets, but the reasons are unknown. As the disease spreads, other muscles may become involved. For example, the diaphragm and chest wall muscles, which are needed for breathing, may be attacked.

The pharyngeal muscles, which are needed for swallowing, may be weakened to the point that swallowing solid foods becomes impossible. Heart muscle is another potential target.

When dermatomyositis attacks the skin, there is a characteristic purplish rash, found mostly on the face and upper chest, although it may occur anywhere on the body. Associated with this rash, patients will often have swelling around the eyes, especially upon rising in the morning. There may also be scaly, reddened eruptions over the small joints of the fingers, sometimes over the eyelids, and occasionally on the shoulders or upper back. These eruptions, which may be somewhat itchy, are so specific that they almost indicate the diagnosis.

Diagnosis

Dermatomyositis often involves a highly characteristic rash on the knuckles and over the upper eyelids, as well as over the cheeks. Measurement of blood levels of muscle enzymes, especially creatine phosphokinase and aldolase, is most useful in diagnosis and in assessing disease activity. An electromyogram (a study of muscle function) may also be done. A muscle biopsy is the only specific diagnostic study and is taken from an involved muscle.

Treatment

Treatment may involve using a corticosteroid drug, although effectiveness is less predictable in these disorders than in some of the other inflammatory diseases. As a result, many rheumatologists turn to one of the cytotoxic drugs (agents that destroy abnormal cells) to work in conjunction with the corticosteroids in attempting to suppress the muscle inflammation and retard the destructive process.

Usually by combining the two classes of drugs, lower and safer doses of both can be used, thereby avoiding some of the more serious side- effects that might be produced when either is used alone in higher doses.

Related Issues Currently Being Researched

Intravenous immune globulin has been shown effective for dermatomyositis resistant to prednisone, but leukapheresis and plasma exchange have not been effective.

Questions to Ask Your Doctor

What is the cause of the dermatomyositis?

If the cause is eliminated, will the disease be eliminated?

Is there remission with the disease? How long can a remission last?

If some of the muscle is destroyed, can the remaining muscle be strengthened and returned to prior ability?

At what rate does this disease usually progress?

Are there any measures to decrease the effects of dermatomyositis?

What medication or medications will you prescribe? What are the side- effects?

Is this a lifetime medication regimen or just while the disease is active?

Approximately how long will it take to stop the destructive process?