皮膚科医が診る筋炎

Myositis and the Skin: Cutaneous Manifestations of Dermatomyositis

はじめに

　筋炎患者が皮膚科を受診する場合，そのほとんどが皮膚筋炎もしくは皮膚筋炎疑いであろうと思われる。自ら皮膚科を訪れる場合もあるが，神経内科や膠原病内科あるいは小児科などから皮膚筋炎疑いの筋炎患者を紹介されることや，呼吸器内科から間質性肺炎を有する患者でやはり皮膚筋炎の可能性について相談されることがある。加えて，皮膚科では筋症状を伴わない無筋症性皮膚筋炎（amyopathic dermatomyositis）患者が他の診療科より多くみられる。

　本稿では，筋炎の中でも特に皮膚筋炎に焦点を絞って，皮膚科医が診断のために重視している臨床所見・病理所見について概説した。さらに他科との連携の必要性や今後の課題についてまとめた。

Abstract

　Idiopathic inflammatory myopathies include dermatomyositis, polymyositis, and inclusion body myositis. Among them, cutaneous manifestations are observed most frequently in dermatomyositis. While dermatomyositis commonly affects the skin and muscles, it can also affect the lungs and other organs. Dermatomyositis presenting clinically and histopathologically with typical cutaneous lesions, but without myositis, is called amyopathic dermatomyositis. Given that the Bohan and Peter criteria cannot distinguish amyopathic dermatomyositis, understanding the characteristic skin manifestations may be essential for diagnosing this condition. The cutaneous manifestations of dermatomyositis are thought to be the result of the Koebner phenomenon, vasculopathy, or photosensitivity; manifestations include various eruptions, such as heliotrope rush, Gottron's sign, Gottron's papules, mechanic's hand, nail-fold bleeding, skin ulcer, vasculitis, flagellate erythema, V-sign, and Shawl sign. The presence of multiple types of eruptions can help diagnose the disease. Several skin diseases, including adult Still's disease, contact dermatitis, and sarcoidosis, can mimic the cutaneous manifestations of dermatomyositis. Skin biopsy is useful for differential diagnoses. Histopathologically, dermatomyositis of the skin is characterized by liquefaction degeneration, vacuolar degeneration, edema, and mucin deposition.

　Dermatologists, neurologists, and rheumatologists are responsible for the diagnosis and management of dermatomyositis, in cooperation with pulmonologists, pediatricians, and pathologists. This review aims to provide clinicians with recent findings regarding skin involvement in dermatomyositis.