Isolated pulmonary and renal IgG4-related disease: a rare dual-organ presentation diagnosed via video-assisted thoracoscopic surgery.

IgG4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder that typically presents with multiorgan involvement. Herein, we report a rare phenotype in which the disease was confined solely to the kidneys and lungs. A man in his 60s presented with a 6-month history of cough and exertional dyspnoea. Imaging revealed bilateral renal enlargement with decreased enhancement, compatible with IgG4-related kidney disease, whereas the pulmonary findings were atypical for IgG4-related lung disease and radiologically mimicked non-specific interstitial pneumonia, making it difficult to determine whether the pulmonary lesions represented part of the same disease process or a separate interstitial lung disease. Serological findings indicated IgG4-RD. To clarify whether both organs were affected by a single systemic process, a thoracoscopic surgical lung biopsy was performed. The histopathological examination confirmed IgG4-positive plasma cell-rich inflammation establishing the diagnosis of IgG4-RD. Corticosteroid therapy resulted in radiological and clinical improvements of both organs. Histopathological evaluation of the lung lesions enabled a unified diagnosis of both the renal and pulmonary manifestations. A stepwise diagnostic approach using lung biopsy facilitated accurate diagnosis and effective treatment.