BK nephropathy in pediatric hematopoietic stem cell transplant recipients.

BK nephropathy is a known cause of renal insufficiency in kidney transplant recipients. Activation of the polyoma virus may also occur in the native kidneys of non-renal allograft recipients. BK nephropathy has only been reported in a few patients after hematopoetic stem cell transplantation (HCT), most being adult patients, and the single reported pediatric case had evidence of hemorrhagic cystitis. The response to anti-viral therapy also seems to differ widely. Here, we describe two cases of BK nephropathy in the native kidneys of HCT recipients exposed to high levels of immunosuppression due to graft-versus-host-disease. Neither of our patients had any evidence of hemorrhagic cystitis. We present definitive renal pathology and detailed chronological evidence of the rising serum creatinine with simultaneous serum and urine BK PCR titers. In one of our cases, anti-viral therapy did not seem beneficial as documented by continued renal dysfunction and serum/urine BK PCR titers. Based on our report, intense immunosuppression in pediatric HCT recipients seems to be involved in the activation of BK virus and BK nephropathy should be suspected even in the absence of hematuria in HCT recipients with unexplained renal dysfunction.