筋炎特異的自己抗体の臨床的意義と有用性

抄録

Idiopathic inflammatory myopathy (IIM) is a heterogenous autoimmune disorder and its subclassification is important in management of the patients. To date, a variety of myositis–specific autoantibodies (MSAs) have been identified and their clinical significance has been elucidated. MSAs can help us not only to diagnose and classify IIMs but also to predict clinical course and prognosis. Among MSAs, anti–aminoacyl–tRNA synthetase (ARS) antibody and anti–melanoma differentiation–associated gene 5 (MDA5) antibody have the strongest association with interstitial lung disease (ILD). ILD with anti–ARS tends to show chronic disease course and respond well to initial glucocorticoid (GC) therapy but often recur. On the other hand, anti–MDA5–positive patients often show acute/ subacute ILD which is resistant to treatment, showing rapidly progressive respiratory distress. For these patients, combined immunosuppressive therapy including high–dose GC, calcineurin inhibitor and intravenous cyclophosphamide pulse in early stage of the disease has been widely used in Japan with increasing evidences for its effectiveness. Anti– transcriptional intermediary factor 1–γ (TIF1–γ), anti–Mi–2, anti–nuclear matrix protein 2 (NXP2) and anti– SUMO–1 activating enzyme (SAE) are associated with dermatomyositis. Moreover, anti–TIF1–γ and anti–NXP2 are associated with malignancy in adult IIM, the latter of which is associated with subcutaneous calcinosis especially in pediatric patients. Anti–signal recognition particle (SRP) and anti–3–hydroxy–3–methylglutaryl–coenzyme A reductase (HMGCR) are associated with immune mediated necrotizing myopathy. Anti–SRP–positive patients tend to show severe muscle weakness, dysphasia and high creatine kinase (CK) level, and anti–HMGCR–positive patients often have episode of statin exposure.

Thus, MSAs can be useful in prediction of clinical course and early determination of treatment strategy for IIM patients.