Thoracic Hyper-IgG4-Related Disease Mimicking Malignant Pleural Mesothelioma.

We report a rare case of a IgG4-related disease presenting with recurrent pleural effusion, pleural thickness and multiple mediastinal lymphadenopathies and no involvement of other extrathoracic organs. A 65-year-old man with a previous asbestos exposure presented with cough and pain discomfort. A large right pleural effusion was detected and evacuated (siero-haematic liquid). With the suspicious of a pleural mesothelioma, a CT-scan before and a 18F-FDG PET/CT-scan later were performed revealing multiple pleural thickenings and multiple mediastinal lymphadenopathies with radiotracer uptake. EBUS-TBNA EBUS-TBNA did not result in a formal pathological diagnosis; thus, multiple pleural biopsy were performed via right thoracoscopy. At pathology the pleura was markedly thickened by a chronic fibroinflammatory process with scattered lymphoid follicles and a large number of mature plasma cells. Immunohistochemistry shows a mixed B (CD20+) and T (CD3+) population of lymphocytes, without light chain restriction and an increased number of IgG4-positive plasma cells. A presumptive diagnosis of IgG4-related disease was formulated. Total body CT-scan excluded other organ involvement. Blood test showed elevated serum IgG4 concentrations (253 mg/dL) and mild elevation of acute-phase reactants (C-reactive protein 10.7 mg/L). Autoimmune profile was negative. A diagnosis of definite IgG4-related disease was made, and treatment with prednisone 50 mg/day was started.