Warfarin-related nephropathy in a patient with renal pelvic cancer

An 83-year-old Japanese man had a history of chronic heart failure due to bradycardia-tachycardia syndrome. He was admitted to our hospital because of macrohematuria and acute kidney injury (AKI), which were detected by an urologist at an outpatient visit. He had a history of recurrent macrohematuria and transurethral resection of bladder tumors twice in the preceding 2 years. He had been on warfarin for 12 years, with a stable international normalized ratio (INR) that was usually less than 2.1. Urinalysis revealed numerous red blood cells (RBCs) and mild proteinuria without RBC casts. His serum creatinine level was elevated to 2.41 mg/dL from 0.96 mg/dL at 3 weeks before admission. INR was 1.44. Hydronephrosis was not observed. Ureteroscopy detected invasive urothelial carcinoma of the renal pelvis, and right laparoscopic nephroureterectomy was performed at 41 days after diagnosis of AKI. The background renal parenchyma displayed tubular obstruction by red blood cell casts and acute tubular injury, which were changes compatible with warfarin-related nephropathy (WRN). Warfarin was discontinued, and the serum creatinine level recovered to 1.66 mg/dL after 3 months. In the present patient with nephrosclerosis, WRN occurred at a therapeutic INR level after 12 years of uneventful warfarin therapy, and the coexisting urothelial malignancy was a unique feature.