Dermatomyositis is one of a group of acquired muscle diseases called inflammatory myopathies. It is characterised by a rash accompanying, or more often, preceding muscle weakness. The rash is described as patchy, bluish-purple discolorations on the face, neck, shoulders, upper chest, elbows, knees, knuckles, and back. Some patients may also develop hardened bumps of calcium deposits under the skin. 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. Patients may also feel fatigue and discomfort and have weight loss or a low-grade fever.
Polymyositis is an inflammatory muscle disease that causes varying degrees of decreased muscle power. The disease has a gradual onset and generally begins in the second decade of life.
Treatment for DM/PM generally consists of 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 heart or lung problems.