IgG4-related disease in the differential diagnosis of lung nodules.

IgG4-related disease is an evolving entity of immune-mediated origin. We report a case of IgG4-related disease mimicking lung cancer with pleural dissemination. A 76-year-old male non-smoker was admitted to our hospital because of chest X-ray abnormality. Chest computed tomography scan showed a lung nodule measuring 26 × 14 mm with tiny nodules on the adjacent pleural surface. Wedge resection by video-assisted thoracoscopic surgery (VATS) was performed to aid diagnosis. Pathological findings of the nodule consisted of lymphoid follicular hyperplasia with lymphoplasmacytic infiltrate, fibrosis, and obstructive vasculitis. Focal and scattered thickening of the pleura with lymphoplasmacytic infiltrate was also observed. The IgG4/IgG ratio in the most prominent area exceeded 80%. Thus, we made a diagnosis of IgG4-related lung and pleural disease. To our knowledge, there has been no report of IgG4-related lung disease mimicking lung cancer with pleural dissemination.