An immunoglobulin G4-related disease mimicking postoperative lung cancer recurrence.

A postoperative lung cancer patient presented with lymphadenopathy, pleural thickening, and 18F-fluorodeoxyglucose (FDG) uptake on a positron emission tomography-computed tomography (PET-CT) scan. Lung cancer recurrence was initially suspected, but bilateral submandibular masses with 18F-FDG uptake indicated the possibility of a systemic disease, such as Mikulicz's disease. High serum immunoglobulin G4 (IgG4) and IgG4-positive plasma cell infiltration in the submandibular glands led to the diagnosis of IgG4-related disease. After systemic steroid therapy, 18F-FDG uptake decreased in both the submandibular glands and the suspected recurrent lesions.