Clinicopathological Features of Myositis and Necrotizing Myopathy: How to Distinguish between Myositis and Muscular Dystrophy on Muscle Pathology Yoshihiko Saito 1 , Ichizo Nishino 1 1Department of Neuromuscular Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry Keyword: 皮膚筋炎 , 抗合成酵素症候群 , 封入体筋炎 , 免疫介在性壊死性ミオパチー , 筋病理 , dermatomyositis , anti-synthetase syndrome , inclusion body myositis , immune-mediated necrotizing myopathy , muscle pathology pp.147-159
Published Date 2021/2/1
DOI https://doi.org/10.11477/mf.1416201727
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In the field of neurology, idiopathic inflammatory myopathy has been classified into four sub-categories, namely, dermatomyositis, anti-synthetase syndrome, inclusion body myositis, and immune-mediated necrotizing myopathy (IMNM), based upon histological and serological findings. Among them, IMNM has features similar to muscular dystrophy, and it may thus be difficult to differentiate between these two conditions, not only clinically but also pathologically, especially in chronic cases and pediatric patients. This is partly because the main pathological feature of both IMNM and muscular dystrophy is myofiber necrosis and regeneration. Furthermore, IMNM patients with anti-SRP antibodies tend to have more prominent muscle atrophy, especially in the shoulder girdle, which mimics the muscle involvement pattern in facioscapulohumeral muscular dystrophy. Some IMNM patients with anti-HMGCR antibodies have onset in their childhood or even in infancy, and may be misdiagnosed with muscular dystrophy. On the other hand, some muscular dystrophies have been reported to show more prominent lymphocyte infiltration than others, which may also mislead muscle pathologists. Nevertheless, these conditions can be distinguished using the relevant histological evaluations, including muscle immunohistochemistry for the MHC and C5b-9 antigens, in addition to appropriate clinical and laboratory examinations including muscle MRI and autoantibody testing.

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