Dermatomyositis
An Autoimmune Inflammatory Muscle Disorder
Dermatomyositis is considered one of the most common of the autoimmune inflammatory muscle disorders.
What is Dermatomyositis
Dermatomyositis (DM) is an autoimmune disease formally classified as one of the inflammatory myopathies (inflammatory muscle diseases). The muscle inflammation of dermatomyositis, which affects multiple muscles causing a condition of polymyositis, is accompanied by a rash. The rash of DM often precedes the muscle disorder. In addition to the rash and myopathy, systemic symptoms such as heart and lung involvement or arthritis may also occur.
Who is Affected?
Dermatomyositis affects people of all ages, including children, and females are more likely to be affected than males. The peak ages affected are 50 years and 5-10 years. The incidence of dermatomyositis/polymyositis appears to be increasing.
Symptoms
The rash of dermatomyositis, which is frequently described as a heloiotrope rash, resembles a patchy, bluish-purple to dusky discoloration that tends to appear on the face, particularly around both eyes, and also on the neck, shoulders, upper chest, elbows, knees, knuckles, and back. A splotchy rash may develop over the neck and upper chest and back in the pattern of a shawl (shawl sign). The rash in DM may also be accompanied by calcium deposits that occur as hard lumps beneath the skin known as Gottron papules.
Gottron papules, which occur in up to 40 percent of adolescents and are seen less often in adults, are frequently found on bony prominenences such as those found on the knuckles, elbow, knees, toes, and feet. The rash in DM may itch (urticaria), appear scaly, appear as white plaques on the insides of the cheeks, or appear as thickening on the palms of the hands (mechanic's hands). At the time of disease onset, the skin manifestations may be the sole complaint.
Symptom severity varies. Most patients survive although death may occur if the muscle weakness is severe or affects the lungs or heart. Children with severe DM may develop muscle contractures, and calcinosis may cause vascular complications. Malignancy may occur in patients with DM, particularly those older than 60 years.
Disease Course
The onset of DM is often severe, and the muscle weakness targets the muscles closest to the trunk of the body. Eventually, patients with DM experience difficulty rising from a seated position, climbing stairs, lifting objects, or reaching overhead. Later in the course of the illness, the muscles distant from the trunk of the body may also be affected. Difficulty in swallowing (dysphagia) may occur, and the muscles may become tender to the touch.
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