IgG4-Related Disease (IgG4-RD) By Cory Perugino, DO, Harvard Medical School Reviewed / Revised Jun 2022 | Modified Sep 2022 View Patient Education Pathophysiology Etiology Pathology Symptoms and Signs Diagnosis Prognosis Treatment Key Points Immunoglobulin G4-related disease (IgG4-RD) is a chronic immune-mediated fibroinflammatory disorder that often manifests with tumor-like masses and / or painless enlargement of multiple organs.