IgG4 disease mimicking lung cancer.

PRESENTATION: A 49-year-old was referred for lobectomy for an incidental finding of a spiculated lung nodule presumed to be primary lung malignancy.

DIAGNOSIS: Histopathological analysis of the resected lung nodule demonstrated the presence of dense lympho-cytoplastic tissue infiltration by immunoglobulin G4 and fibrosis, consistent with IgG4 disease.

TREATMENT: The patient was managed conservatively, with ongoing radiographic surveillance for evidence of extra-thoracic involvement.

DISCUSSION: Immunoglobulin G4 related disease (IgG4-RD) is a rare and poorly understood multi-system inflammatory condition that may mimic malignancy in the lung.