Microscopic polyangiitis masquerading as a pancreatic neoplasm with multiple lung metastases

A 71-year-old man was admitted to our hospital with right lower abdominal pain. Blood analysis indicated severe inflammation, and abdominal CT revealed a pancreatic head tumour and multiple lung nodules. The level of a tumour marker was high. Pancreatic cancer with multiple lung metastases was suspected; however, because the mass was not detected via endoscopic ultrasonography, it was not biopsied. The serum creatinine level increased rapidly with a urine disorder, and myeloperoxidase-antineutrophil cytoplasmic antibody staining was positive. Severe rapidly progressive glomerulonephritis (RPGN) and microscopic polyangiitis were diagnosed, and high-dose glucocorticoid treatment was started. The patient's high fever returned to normal, and the serum creatinine level declined. Because the RPGN was severe, cyclophosphamide was administrated, and the glucocorticoid was tapered. The pancreatic tumour regressed, the lung nodules disappeared, and the tumour marker level normalised during the treatment. Renal function improved, and maintenance haemodialysis was avoided.