In one study, the incidence of the disease among the Bantu in South Africa was 10 times the incidence in whites. DM, although primarily a disease of adults, also is seen in children, usually those aged 5-14 years. The heliotrope rash is a confluent, purple-red, edematous periorbital eruption. Associated findings include conduction defects, arrhythmias, myocarditis, interstitial lung disease, and aspiration pneumonia. The etiology is unknown.
Muscle inflammation is immune mediated.
Creatine kinase, aldolase, myoglobin, lactate dehydrogenase, aspartate aminotransferase, and alanine aminotransferase levels may be elevated. In practice, usually only the creatine kinase and aldolase levels are determined. The erythrocyte sedimentation rate usually is elevated. Myoglobinuria may be present. MRI examination MRIs show signal intensity abnormalities of muscle due to inflammation, edema, or scarring.