IgG4-related pulmonary pseudotumor and pleuritis mimicking lung cancer and asbestos plaque: A case report

We report the case of a 70-year-old man who presented with a two-month history of cough. He had a history of asbestos exposure. Chest imaging revealed a mass on the right upper lobe, bilateral hilar and mediastinal lymphadenopathies, bilateral pleural thickening, and partial calcification of the right pleura. Lung cancer and asbestos-related pleural disease were suspected initially. However, neither transbronchial lung biopsy nor computed tomography-guided percutaneous needle lung biopsy demonstrated evidence of malignancy. Subsequent video-assisted thoracoscopic surgery revealed storiform fibrosis, dense lymphoplasmacytic infiltration, and numerous IgG4-positive plasma cells in the lung mass along with asbestos bodies. The pleura exhibited similar histopathological features. The patient's elevated serum IgG4 levels, in combination with these histological features, fulfilled both the 2019 ACR/EULAR classification criteria and the Japanese comprehensive diagnostic criteria for IgG4-related disease (IgG4-RD). The patient was treated with oral prednisolone, resulting in resolution of the lung mass, symptom improvement, and a decline in serum IgG4 levels. IgG4-RD is an immune-mediated condition characterised by T helper type 2 cell activation, elevated serum IgE levels, and regulatory T cell (Treg) dysfunction. The development of Treg dysfunction after asbestos exposure suggests a potential mechanistic link between asbestos and the pathogenesis of IgG4-RD. This case highlights the diagnostic challenges posed by IgG4-related lung disease, which can mimic malignancy and asbestos-related pathology, underscoring the importance of biopsy for accurate diagnosis. It also suggests a possible association between asbestos exposure and IgG4-RD development.