Abstract:

OBJECTIVE: To evaluate the diagnostic value of myxovirus resistance A (MxA) expression in the cytoplasm of myofibers in the diagnosis of dermatomyositis (DM).
METHODS: We assessed the sensitivity and specificity of the sarcoplasmic expression of MxA in muscles with DM by immunohistochemistry in consecutive cases of DM (n = 34) and other idiopathic inflammatory myopathies (n = 120: 8 with polymyositis, 16 with anti-tRNA-synthetase antibody-associated myositis, 46 with immune-mediated necrotizing myopathy, and 50 with inclusion body myositis) and compared them with conventional pathologic hallmarks of DM, including perifascicular atrophy (PFA) and membrane attack complex (MAC) deposition on endomysial capillaries.
RESULTS: The sensitivity and specificity of sarcoplasmic MxA expression were 71% and 98%, respectively. While the specificity was almost comparable to that of PFA and capillary MAC deposition, the sensitivity was higher, with PFA showing 47% sensitivity and 98% specificity and capillary MAC deposition showing 35% sensitivity and 93% specificity. Of note, in patients with DM with typical skin rash but no PFA, 44% of the samples showed sarcoplasmic MxA expression, which was higher than the 17% sensitivity of capillary MAC deposition in the population.
CONCLUSIONS: Sarcoplasmic MxA expression detected by immunohistochemistry is a more sensitive marker of DM than the conventional hallmarks, indicating its practical utility in the diagnosis of DM. It may well be included in the routine immunohistochemistry panel for myositis.
CLASSIFICATION OF EVIDENCE: This study provides Class II evidence that immunohistochemistry-detected sarcoplasmic MxA expression accurately identifies patients with dermatomyositis.

日本語要旨:

厚生労働省指定難病の一つである皮膚筋炎の診断において、筋細胞上に発現するMxA(ミクソウイルス抵抗蛋白質A)が、従来のものと比較して最も優れた診断バイオマーカーになることを明らかにしました。 皮膚筋炎は筋肉と皮膚に炎症をきたし、筋力低下や皮膚の発疹を起こす疾患です。間質性肺炎やがんといった生命に関わる合併症を伴うこともあることから、より早期からの正確な診断が求められます。研究グループは、皮膚筋炎患者の筋細胞上に発現するMxAを検出することで、従来の診断方法に比べて高感度で診断できることを発見しました。この研究成果は、今後の皮膚筋炎の診断精度の向上に大きく貢献するものと期待されます。 本論文は当該号の表紙を飾りました。