[Immunoglobulin G4-related lung disease: Case report and literature review].

We report the case of a 61-year-old man with a pulmonary nodule discovered while staging the metastasis of a squamous cell carcinoma. No primary cancer was found. Histological examination of the resected specimen (lingula) was in favor of IgG4-related inflammatory pseudotumor. Histological criteria were described in 2012, combining a dense lymphoplasmacitic infiltrate rich in IgG4-positive plasma cell, storiform fibrosis and obliterative phlebitis. IgG4/IgG plama cell ratio>40 % is mandatory for histological diagnosis of IgG4-related disease. This is a rare and often underdiagnosed disease. Diagnostic criteria are now defined and consensual, combining clinical signs, biology and histology.