Isolated IgG4-related lung disease: a case report.

BACKGROUND: IgG4-related disease (IgG4-RD) represents a chronic, immune-driven fibroinflammatory condition capable of affecting diverse organ systems; within this spectrum, pulmonary involvement (IgG4-RLD) remains comparatively uncommon. This case report outlines the clinical, imaging and pathological features of a patient with IgG4-related lung disease. CASE DESCRIPTION: We report a 60-year-old male patient with recurrent fever, chest pain, and cough with hemoptysis. Chest computed tomography (CT) initially showed right upper lobe lesions suggestive of pneumonia, but the patient failed to respond to multiple courses of antibiotics including levofloxacin, nemonoxacin malate, ceftizoxime, and amoxicillin. Further investigations revealed significantly elevated serum IgG4 level (266 mg/dL). Endobronchial ultrasound-guided transbronchial lung cryobiopsy (EBUS-GS-TBLC) confirmed dense lymphoplasmacytic infiltration in the lung tissue, with IgG4-positive plasma cells >50 per high powered field (HPF) and IgG4-positive/IgG-positive cell ratio >50%, consistent with the diagnosis of IgG4-related interstitial lung disease. The patient was treated with oral cyclosporine and mycophenolate mofetil, resulting in significant clinical and radiological improvement. CONCLUSIONS: IgG4-RLD should be considered in the differential diagnosis of patients with pulmonary lesions unresponsive to antibiotic therapy. Comprehensive evaluation including serum IgG4 measurement and targeted pathological biopsy is essential for accurate diagnosis. Early initiation of immunosuppressive therapy can effectively improve outcomes and prevent disease progression.