*Purpose: Patients with non-renal organ transplantation may suffer BK-viral nephropathy (BKVN) of their orthotopic kidneys by reactivation of their own viral population living in latency of urothelial cells. We aimed to know if these patients with BKVN after non-renal organ transplantation differ from renal transplant (TX) patients with BKVN.

*Methods: We followed retrospectively the clinical course of non-renal transplant patients with BKVN.

*Results: During the last 14 years we have seen 10 patients with biopsy-proven and 2 with highly suggestive BKVN after non-renal organ transplantation (9 lung TX patients, 2 heart TX patients, 1 HSCT patient) and 1 other biopsy-proven patient without being transplanted at all (altogether n=13). Eleven of the patiemts were men (85%). Six patients had end stage renal disease (ESRD, 46%), and 6 had progressive renal insufficiency with eGFR <30mL/min (46%). Diagnosis was established 74+/-67 months after transplantation in 12 patients. Maximum viremia was 3.3+/-5.6 million and maximum viruria 4.4+/-6.7 billion cop/mL. Two patients after lung transplantation received a renal TX 49 and 8 months respectively after ESRD, when viremia was down to 0 and 1500 cop/mL respectively; however, both lost their renal graft 7 and 22 months respectively after renal transplantation because of recurrent BKVN. In one of these 2 patients the BKV subtype of the recurrent BK virus was known and was identic with the subtype seen after non-renal organ transplantation before renal transplantation. One patient after heart transplantation with high viruria over 6 and high viremia over 2 years deveoped urothelial carcinoma with SV40 positive tumor cells.

*Conclusions: BKVN of the orthotopic kidneys is seen preferentially after lung transplantation. In patients with BKVN after non-renal organ transplantation diagnosis is established late and with high viral load of long persistence. The patients develop severe renal insufficiency and often ESRD. Both patients with renal transplantation lost their renal graft early because of recurrent BKVN despite low viremia at the time of renal transplantation. One other patient developed BKV-induced urothelial carcinoma. – The course of BKVN of orthotopic kidneys after non-renal transplantation seems to be more malignant than BKVN after renal transplantation.

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