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.
Muscle inflammation is immune mediated.
In practice, usually only the CPK and aldolase are tested. CPK is the most sensitive and specific and is usually 5-50 times above normal. MRI has shown signal abnormalities of muscle due to inflammation, edema, or scarring. However, the biopsy occasionally may be normal due to patchy involvement. Generally, the disease is insidious with gradual progression.