A case of immunoglobulin G4-Related disease with pleural effusion, requiring exclusion of tuberculous pleurisy

Immunoglobulin G4 (IgG4)-related pleurisy is a rare type of IgG4-related disease. We present the case of a 69-year-old woman with left pleural effusion and elevated adenosine deaminase levels. Initially, tuberculous pleuritis was suspected; however, the bacterial cultures and polymerase chain reaction test results for tuberculosis were negative. Thoracoscopic pleural biopsy revealed dense lymphocytic infiltrates with large numbers of IgG4-positive plasma cells. The ratio of IgG4-positive to IgG-positive plasma cells exceeded 40%. The patient was diagnosed with IgG4-related disease.