IgG4-related sclerosing disease involving the superior vena cava and the atrial septum of the heart.

A 55-year-old woman presented with frequent episodes of syncope due to sinus pauses. During ambulatory Holter monitoring, atrial fibrillation and first-degree atrioventricular nodal block were observed. Magnetic resonance imaging and CT scans showed a tumor-like mass from the superior vena cava to the right atrial septum. Open chest cardiac biopsy was performed. The tumor was composed of proliferating IgG4-positive plasma cells and lymphocytes with surrounding sclerosis. The patient was diagnosed with IgG4-related sclerosing disease. Because of frequent sinus pauses and syncope, a permanent pacemaker was implanted. The cardiac mass was inoperable, but it did not progress during the one-year follow-up.