High serum immunoglobulin G4-related retrosternal fibrosclerosis.

A 65-year-old man with a history of exposure to asbestos complained of left leg edema. Computed tomography showed a flat, symmetrical, and longitudinal retrosternal thickening in addition to a presacral tumor. Retroperitoneal fibrosis was suspected. Serum immunoglobulin G4 (IgG4) levels were elevated (213 mg/dL). Thoracoscopic biopsy was performed. Histopathologic findings showed fibrotic tissue accompanied by proliferation of IgG4-positive plasma cells (proportion of IgG4/IgG-positive plasma cells ≥70%) indicative of multifocal fibrosclerosis.