IgG4-Related Lung Disease Presenting as an Indeterminate Pulmonary Mass in a Young Woman With Prior Tuberculosis: A Case Report.

IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder that may rarely involve the lungs. Its pulmonary manifestations are variable and can present as an indeterminate mass, posing a significant diagnostic challenge. We report a 32-year-old woman with prior pulmonary tuberculosis and tuberculosis-related cervical myelopathy who was found to have a right upper lobe lesion during re-evaluation for persistent cough. Two image-guided biopsies were inconclusive, showing inflammatory tissue only, and the lesion was initially treated as a tuberculoma. However, the lesion persisted and enlarged despite completion of anti-tuberculous therapy, while positron emission tomography-computed tomography (PET-CT) demonstrated fluorodeoxyglucose avidity, raising suspicion for malignancy. She underwent uniportal video-assisted thoracoscopic right upper lobectomy with lymphadenectomy. Histopathological examination showed dense lymphoplasmacytic infiltration, storiform fibrosis, and obliterative phlebitis, with immunohistochemistry demonstrating an IgG4/IgG plasma cell ratio of 40%, consistent with IgG4-related lung disease. She recovered well postoperatively and remained well on follow-up. This case emphasizes that IgG4-related lung disease should be considered in the differential diagnosis of persistent pulmonary masses, especially when biopsies are inconclusive and prior granulomatous infection confounds the clinical picture.