In DM, complement-mediated damage to endomysial vessels and to microvasculature of the dermis is present. Patients with advanced age, cardiac or pulmonary involvement, or dysphagia have a higher mortality. In one study, the incidence of the disease among the Bantu in South Africa was 10 times incidence in whites. Dermatomyositis, although primarily an adult disease, also is seen in children, usually aged 5-14 years. Muscle pain may be reported at rest or with use.
Symptoms develop over weeks to months.
Arthralgias often are reported. In dermatomyositis, a characteristic heliotrope rash may precede or accompany muscle weakness. The heliotrope rash is a confluent, purplish-red, edematous periorbital eruption. Associated findings include conduction defects, arrhythmias, myocarditis, interstitial lung disease, and aspiration pneumonia. The etiology is unknown.