Definition of Dermatomyositis

Dermatomyositis: A chronic inflammatory disease of skin and muscle which is associated with areas of slightly raised reddish, scaly rash. The rash can be on the bridge of the nose, around the eyes, or on sun-exposed areas of the neck and chest. Classically, however, it is over the knuckles. When the characteristic inflammation of the muscle (myositis) occurs without skin disease, the condition is referred to as polymyositis.

Dermatomyositis is one of a group of acquired muscle diseases called inflammatory myopathies. The disease has a subacute (somewhat short and relatively severe) onset. It affects both children and adults. Females are more often affected than males. Dermatomyositis is characterized by a rash accompanying, or more often, preceding muscle weakness. The most common symptom is muscle weakness, usually affecting those muscles that are closest to the trunk of the body (proximal). Eventually, patients have difficulty rising from a sitting position, climbing stairs, lifting objects, or reaching overhead. In some cases, distal muscles (those not close to the trunk of the body) may be affected later in the course of the disease. Trouble with swallowing (dysphagia) may occur. Occasionally, the muscles ache and are tender to touch. Some patients develop hardened bumps of calcium deposits under the skin. Patients may also feel fatigue and discomfort and have weight loss or a low-grade fever.

Treatment commonly involves a steroid drug called prednisone. For patients in whom prednisone is not effective, other immunosuppressants such as azathioprine and methotrexate may be prescribed. Recently, a drug called intravenous immunoglobulin was shown to be effective and safe in the treatment of the disease. Physical therapy is usually recommended to preserve muscle function and avoid muscle atrophy. Most cases of dermatomyositis respond to therapy. The disease is usually more severe and resistant to therapy in patients with associated cardiac or pulmonary problems.

Both polymyositis and dermatomyositis can sometimes be associated with cancers, including lymphoma, breast, lung, ovarian, and colon cancer. The cancer risk is reported to be much greater in those older than 55 years old, with dermatomyositis rather than polymyositis.