Clinically amyopathic dermatomyositis

Purpose of review Clinically amyopathic dermatomyositis (CADM) is a unique subset of dermatomyositis, with typical skin manifestations of dermatomyositis but little or no evidence of myositis. This review focuses on updates on epidemiology, clinical manifestations, and autoantibody profiles in patients with CADM. Recent findings A population-based survey of dermatomyositis conducted in the United States revealed that overall age-adjusted and sex-adjusted incidence of CADM was 2.08 per 1 million persons. CADM consisted of approximately 20% of dermatomyositis. In general, late-onset myositis was infrequent. There was no apparent difference in frequency of internal malignancy or interstitial lung disease between CADM and classic dermatomyositis. However, anecdotal and retrospective case reports from eastern Asia showed a relatively high incidence of rapidly progressive interstitial lung disease, which is often fatal, in patients with adult-onset and juvenile-onset CADM. Finally, RNA helicase encoded by melanoma differentiation-associated gene 5 was identified as an autoantigen recognized by anti-CADM-140 antibody, which is associated with CADM and rapidly progressive interstitial lung disease. Summary CADM is a distinct clinical entity with unique clinical features and autoantibody profiles different from classic dermatomyositis.