BK Virus Associated Nephropathy (BKVAN) in a Lung Transplant Recipient in the Setting of Augmented Immunosuppression

Introduction Acute kidney injury (AKI) and chronic kidney disease (CKD) are common amongst lung transplant recipients due to calcineurin inhibitor (CNI) use. We describe a case of acute BK virus associated nephropathy (BKVAN) in a lung transplant recipient with baseline CKD stage 4. Case Report A 73-year-old male status post right single lung transplant eight years prior for tobacco-induced emphysema presented for admission for acute cellular rejection (ACR). He was treated with methylprednisolone 10 mg/kg x three days per protocol. His renal function was within normal range pre-transplant, but had gradually progressed to CKD 4 with a new baseline creatinine of 2.4 at time of admission. Progressive CKD was attributed to CNIs. He had been placed on a CNI sparing regimen with everolimus more than one year prior to index admission with continued progression of renal dysfunction. Upon initiation of methylprednisolone, creatinine began to rise and eventually peaked to 4.3. UA showed trace protein but was otherwise bland, urine microscopy with muddy brown granular casts and renal tubular epithelial (RTE) cells. Renal ultrasound was poor quality showing possible small right kidney, left kidney not imaged. As part of his work-up, a BK virus PCR from his urine was sent and positive, with greater than 162 million IU/mL: serum BK PCR returned at 146,000 IU/mL. Microscopic urine analysis demonstrated RTE cells consistent with decoy cells, supportive of viral injury. A kidney biopsy was considered, however not performed because of chronic anticoagulation for a recent history of venous thromboembolism. Over the next several days, creatinine decreased minimally to 3.76. Patient was discharged home with outpatient nephrology follow up and had serial serum BK PCR tests for disease monitoring.In the setting of declining pulmonary function testing and ACR, we were unable to decrease immunosuppression without risking further deterioration of the lung allograft. Summary To our knowledge, this is the ninth reported case of BKVAN after lung transplant. BK viremia and BKVAN are likely an under-diagnosed etiology of CKD and AKI in the lung transplant population. We speculate that our patient had undiagnosed low level BK viremia that was affecting his renal function chronically, but when treated with high dose steroids, led to an acute BK nephropathy.