Section 5. Bone, Joint, and Muscle Disorders

Chapter 68. Autoimmune Disorders of Connective Tissue

Topics: Introduction | Systemic Lupus Erythematosus | Scleroderma | Sjögren's Syndrome | Polymyositis and Dermatomyositis | Mixed Connective Tissue Disease | Relapsing Polychondritis | Eosinophilic Fasciitis

Polymyositis and Dermatomyositis

Polymyositis is characterized by inflammation and degeneration of the muscles; dermatomyositis is polymyositis accompanied by skin inflammation.

These disorders result in disabling muscle weakness. The weakness typically occurs in the shoulders and hips but can affect muscles symmetrically throughout the body.

Polymyositis and dermatomyositis usually occur in adults from ages 40 to 60 or in children from ages 5 to 15 years. Women are twice as likely as men to develop either disorder. In adults, these disorders may occur alone or as part of other connective tissue disorders, such as mixed connective tissue disease.

The cause of polymyositis and dermatomyositis is unknown. Viruses or autoimmune reactions may play a role. Cancer may also trigger polymyositis and dermatomyositis--it is possible that an immune reaction against cancer may be directed against a substance in the muscles.

Symptoms

In polymyositis, the symptoms are similar for people of all ages, but the disorder usually develops more abruptly in children than in adults. Symptoms, which may begin during or just after an infection, include symmetrical muscle weakness (particularly in the upper arms, hips, and thighs), joint pain (but often little muscle pain), difficulty in swallowing, fever, fatigue, and weight loss. Raynaud's phenomenon (in which the fingers suddenly become very pale and tingle or become numb in response to cold or emotional upset (see Section 3, Chapter 34)) occurs more in people who have polymyositis along with other connective tissue disorders.

Muscle weakness may start slowly or suddenly and may worsen for weeks or months. Because muscles close to the center of the body are affected most, tasks such as lifting the arms above the shoulders, climbing stairs, and getting out of a chair can become very difficult. If the neck muscles are affected, even raising the head from a pillow may be impossible. Weakness in the shoulders or hips can confine a person to a wheelchair or bed. Muscle damage in the upper part of the esophagus can cause swallowing difficulties and regurgitation of food. The muscles of the hands, feet, and face, however, are not affected.

Joint aches and inflammation occur in about one third of the people. The pain and swelling tend to be mild.

Polymyositis usually does not affect internal organs other than the throat and esophagus. However, the lungs and heart may be affected, causing shortness of breath and a cough.

In dermatomyositis, all the symptoms of polymyositis occur. In addition, rashes tend to appear at the same time as muscle weakness and other symptoms. A shadowy-red or purplish rash (heliotrope rash) can appear on the face. A reddish-purple swelling around the eyes is characteristic. Another rash, which may be scaly, smooth, or raised, may appear almost anywhere on the body but is especially common on the knuckles and sides of the hands. The nail beds may redden. When the rashes fade, brownish pigmentation, scarring, shriveling, or pale depigmented patches may develop on the skin.

Diagnosis

Doctors use the following criteria to make the diagnosis of polymyositis or dermatomyositis: muscle weakness at the shoulders or hips, a characteristic rash, increased blood levels of certain muscle enzymes (especially creatine kinase), characteristic changes in muscle tissue obtained by biopsy and observed under a microscope, and abnormalities in the electrical activity of muscles measured by electromyography (see Section 6, Chapter 77). Laboratory tests are helpful but cannot specifically identify polymyositis or dermatomyositis. Blood levels of creatine kinase are often much higher than normal, indicating muscle damage. These enzymes are measured repeatedly in blood samples to monitor the disorder; the levels usually fall to normal or near normal with effective treatment. Magnetic resonance imaging (MRI) may also show areas of inflammation and help the doctor select a site for biopsy. Special tests performed on muscle tissue samples may be needed to rule out other muscle disorders.

Treatment and Prognosis

Restricting activities when the inflammation is most intense often helps. Generally, a corticosteroid, usually prednisone, given by mouth in high doses slowly improves strength and relieves pain and swelling, controlling the disease. After about 6 to 12 weeks, when the muscle enzyme levels have returned to normal and muscle strength has returned, the dose is gradually decreased. Most adults must continue taking a low dose of prednisone for many years or even indefinitely to prevent a relapse. After about a year, children may be able to stop taking the drug and stay symptom-free.

Occasionally, the side effects of prednisone actually worsen the symptoms (see Section 5, Chapter 67). In these cases, an immunosuppressive drug (methotrexate, cyclophosphamide, chlorambucil, azathioprine, or cyclosporine) is used instead of or in addition to prednisone. When other drugs are ineffective, gamma globulin (a substance that contains large quantities of many antibodies) may be given intravenously.

When polymyositis is associated with cancer, it usually does not respond well to prednisone. However, the condition usually improves if the cancer can be successfully treated.

Adults with severe, progressive disease who develop difficulty in swallowing, malnutrition, pneumonia, or respiratory failure may die from the disease.