Native kidney BK nephropathy: A case report

Historically, BK virus nephropathy was thought to be a disease of kidney allografts that only affected renal transplant recipients. BKN is getting more frequently diagnosed as a cause of kidney disease in immunosuppressed patients. Here, we describe a biopsy‐proven native kidney BKN in an allogeneic stem cell transplant patient. The BK virus was first isolated in 1971 from the urine of a renal transplant patient,1 but it was not until early 80s when Polyomavirus (BK and JC viruses) infections were described in renal transplant recipients.2, 3 At that time, native kidney BKN was considered to occur sporadically with few reports in lymphoma patients and solid organ transplant recipients. More cases of native kidney BKN have been reported in the new millennium with thoughts of under diagnoses of this entity.4 In the general population, 70%‐90% of individuals carry anti‐bodies to BK virus.5 The primary infection occurs as either a mild respiratory illness or asymptomatic infection during childhood, followed by viral latency usually in the urothelium and renal tubular epithelial cells.6, 7 Reactivation of BK infection may occur under conditions of immunosuppression, with usual manifestation being hematuria when it is limited to the urothelium.8, 9 Tissue diagnosis by a kidney biopsy is needed for detection of intrarenal Polyomavirus (PV) using SV40 stain.