What happened, in summary

This 31-year-old East Asian woman was admitted in July 2021 after 1 month of fever, reduced appetite, and fatigue. She had developed a high fever of 39 °C, gross hematuria, and an episode of fainting. Laboratory testing showed severe kidney involvement: proteinuria of 851 mg/24 hours, serum creatinine of 609 μmol/L, hemoglobin 76 g/L, anti-MPO-ANCA 138 AU/mL, and anti-GBM antibody 147 AU/mL. At the same time, chest CT found pulmonary nodules with heterogeneous enhancement, raising concern for lung cancer. Whole-body PET-CT favored an inflammatory lung nodule rather than cancer, and surgery was not recommended because of the nodule's small size and location. Kidney biopsy consultation showed crescents of varying stages, supporting ANCA-associated small-vessel vasculitis kidney damage, also described as type III crescentic glomerulonephritis. She was diagnosed with ANCA-associated vasculitis affecting the kidneys and lungs. Treatment was intensive: 2 cycles of methylprednisolone pulse therapy for 3 days, followed by oral steroids, cyclophosphamide, plasma exchange, and hemodialysis. Her renal function gradually improved, and she eventually became independent from dialysis. Hemoglobin normalized, proteinuria resolved, and both ANCA and GBM antibodies turned negative. Oral steroids were tapered and then replaced with azathioprine 100 mg daily for maintenance. At follow-up on 20 November 2023, serum creatinine was 93 μmol/L, urine protein was negative, ANCA and GBM antibodies remained negative, and CT showed significant improvement in the pulmonary nodules. Her story is a lung-cancer mimic rather than confirmed lung cancer, with lung findings improving after immune-directed treatment rather than surgery or cancer therapy.