Rapid Progression of Acute Interstitial Pneumonia in a Patient with Low MDA-5 Antibody Titer.

BACKGROUND Melanoma differentiation associated gene-5 antibody (MDA-5 Ab) is one of the diagnostic autoantibodies that appears in idiopathic inflammatory myopathies (IIMs). Unlike when other autoantibodies are positive, when this antibody is positive, there is less characteristic muscle involvement. However, this MDA-5 Ab-positive myopathy presents extremely rapid progression of interstitial lung disease, resulting in a high mortality rate. Previous studies reported that the prognosis of this lung disease will be determined by the titer and suggest that low titers of MDA-5 antibody can indicate a good prognosis in associated interstitial lung disease. CASE REPORT Our case describes a 55-year-old woman who presented with acute respiratory symptoms and dyspnea. After hospitalization, symptoms and chest imaging worsened rapidly, and the radiology image of lung disease featured interstitial changes not seen in typical infections. We treated the patient with a high-flow oxygen nasal cannula, empirical antibiotics, and a systemic steroid. While treatment for a disease of unknown cause was continued, low titer of MDA-5 antibody was identified. CONCLUSIONS This case suggests 2 points to consider about non-infectious interstitial changes with acute respiratory distress syndrome. First, when treating rapidly progressing interstitial pneumonia of an unknown cause, it is recommended to consider lung involvement of MDA-5 Ab dermatomyositis. Second, a low titer of MDA-5 Ab can be associated with better prognosis in this MDA-5 Ab dermatomyositis-related lung disease.