A Rare Cause of Kidney Failure: Native Kidney BK Polyomavirus Nephropathy after Lung Transplant

Introduction: BK polyomavirus nephropathy (BKVN) is a common complication of kidney transplantation, affecting 1-10% of renal transplant patients. It is rare in the native kidneys and is most often reported following hematopoietic stem cell transplantation. We present a case of native kidney BKVN leading to end-stage kidney disease (ESKD) in a lung transplant recipient. Case Description: A 71-year-old woman with history of obliterative bronchiolitis who received a bilateral lung transplant in 2021 (on everolimus, mycophenolate mofetil, and prednisone) with course complicated by ischemic stroke, intermittent hypotension, and frequent urinary tract infections was referred to the renal clinic with progressive renal failure in 2023. At the time of referral her serum creatinine had risen from 1 to 2 mg/dl over 12 months. Workup was remarkable for pyuria with positive urine culture. Kidney ultrasound was without obstruction and serologies were negative. She underwent a kidney biopsy which revealed BK polyomavirus nephropathy with 40% interstitial fibrosis and tubular atrophy. Despite minimizing immunosuppression, her kidney function continued to worsen. She was started on cidofovir and, though her BK serum viral load improved, her renal function deteriorated and she developed ESKD. She is now on peritoneal dialysis undergoing evaluation for kidney transplant. Discussion: BK nephropathy of the native kidneys in non-kidney solid organ transplant recipients is gaining recognition as an important cause of renal failure and progression to ESKD. Patients with unexplained renal failure after non-renal solid organ transplant may benefit from screening for BK virus to facilitate early diagnosis of BK polyomavirus nephropathy.Viral inclusions within the tubuler epithelial cells.Postive SV40 staining of tubular epithelial cells.