Isolated Pulmonary IgG4-related Disease Presenting as Cavitary Lung Lesions and Mass Formation, Treated with Rituximab Monotherapy

IgG4-related disease (IgG4-RD) is a rare immune-mediated condition characterized by tumefactive and fibroinflammatory lesions that can affect nearly any anatomical site.Isolated pulmonary involvement is uncommon, as the disease typically presents with systemic manifestations.We report the case of a 50-year-old male, a heavy smoker, who presented with chest pain, hemoptysis, and intermittent fever.An extensive workup ruled out malignancy, infections, and other systemic diseases, ultimately leading to the diagnosis of IgG4-related disease, presenting as an inflammatory myofibroblastic tumor.Imaging revealed a unique presentation with cavitations and cavitary consolidation, along with more commonly reported features such as a mass, mild pleural effusion, and mediastinal lymphadenopathy.Given the potential for irreversible organ damage, the patient was treated with rituximab monotherapy, resulting in significant improvement and near-resolution of the lung lesions on follow-up.This case highlights the importance of maintaining a high index of suspicion for IgG4-related disease when other diagnoses have been ruled out in lung lesions, particularly when lymphoplasmacytic infiltration is present in the affected tissues.