Thoracoscopic resection for a pulmonary nodule with the infiltrate of IgG4-positive plasma cells.

This report describes a rare case of IgG4-related lung disease that was difficult to distinguish from lung cancer. CT revealed a well-demarcated round tumor in S10 of the right lung of a 56-year-old man suspected of having lung cancer. PET revealed high fluorodeoxyglucose uptake with a maximum standardized uptake value of 14.0. Because primary lung cancer was strongly suspected, lower lobectomy was performed via the thoracoscopic approach without mini-thoracotomy. Histopathology showed lymphoplasmacytic infiltration. Immunostaining revealed numerous IgG4-positive plasma cells diffusely infiltrating the tumor. Serum IgG4 levels increased, thereby confirming the diagnosis of IgG4-related lung disease.