Optimal management of interstitial lung disease associated with dermatomyositis/polymyositis: lessons from the Japanese experience

Interstitial lung disease (ILD) is a serious complication in dermatomyositis (DM) and polymyositis (PM). In Japan, patients with DM/PM develop acute life-threatening ILD with high frequency. Physicians in Japan have shown the following: refractory acute/subacute (A/S)-ILD is not a rare complication in DM and amyopathic DM (ADM); anti-anti-melanoma differentiation-associated gene 5 (anti-MDA5) antibody (Ab) is closely related to A/S-ILD with poor outcomes in DM/ADM; and poor prognostic factors in A/S-ILD in DM/PM are ADM, DM with low creatine kinase elevation, positivity for anti-MDA5 Ab, serum ferritin elevation, and consolidation with ground-glass opacities on high-resolution computed tomography. There are subtypes in DM/PM-ILD: refractory DM/ADM A/S-ILD positive for anti-MDA5 Ab with poor prognosis; DM A/S-ILD with glucocorticoid (GC) resistance; PM A/S-ILD with GC sensitivity; chronic ILD positive for anti-aminoacyl-tRNA-synthetases (anti-ARS) Abs with GC responsiveness; and C-ILD negative for anti-ARS Abs. For patients with A/S-ILD with poor prognosis, initial combination therapy with cyclosporine and cyclophosphamide in addition to GC has been developed, which rescues 50%–80% of the patients, although elucidation of the efficacy of the combination therapy is required. A/S-ILD with potentially fatal outcomes is found worldwide, not only in Japan. Clinicians caring for patients with DM/PM should be cautious when dealing with A/S-ILD and treat the patients based on clinical subtypes.