Immunoglobulin G4-related lung disease presenting with a mediastinal mass

Immunoglobulin G4-related disease (IgG4-RD) is a recently identified systemic disease characterized by increased IgG4 level in serum and plasma cell infiltration resulting in “storiform fibrosis”. Although lung involvement is rare, clinical presentation is highly variable, including mediastinal lymphadenopathy, interstitial pneumonia, and pleural effusion. Glucocorticoid therapy is accepted as the mainstay treatment in IgG4-RD. Here, we present an IgG4-related lung disease (IgG4-RLD) case who was admitted to the hospital with chest pain; found out to have a mediastinal mass. IgG4-RLD was diagnosed based on histopathological features and a high blood IgG4 level. The patient’s steroid therapy was effective and there were no steroid-related side effects.