IgG4-related disease of the lung: a rare differential diagnosis to lung cancer after positive positron emission tomography and biopsy.

Immunoglobulin G4-related disease is a rare immune-mediated condition that often causes serious diagnostic problems. Symptoms are unspecific, and several organs can be involved. To date, IgG4-related lung disease has seldom been reported in literature. Nevertheless, a variety of pulmonary involvement has been described, which can mimic malignancy. The gold standard for the diagnosis is the identification of typical histopathological features, even if diagnostic biomarker such as serum IgG4 concentration can be an indicator for a more aggressive course of the disease