Purpose: BK polyoma nephropathy (BKPyN) is a well-recognized cause of allograft dysfunction and loss after kidney transplant. Despite increased recognition, it is unclear if changes on histopathology associate with BK viral load, degree of allograft dysfunction, or eventual allograft loss.

Methods: We performed a single-center retrospective analysis of all biopsy proven BKPyN cases in kidney transplant recipients (KTRs) transplanted between 2002 and 2014. Outcome variables of time from transplant to diagnosis, BK viral load at biopsy, change in estimated glomerular filtration rate (eGFR) (MDRD) from post-transplant nadir to biopsy, and allograft loss from BKPyN were recorded. Biopsies were re-evaluated by a single pathologist blinded to clinical data and classified into grades A (early), B (florid), and C (late sclerosing) using the criteria set by the Banff Working Group on Polyomavirus nephropathy. The association between the histologic grade of nephropathy and the above outcome variables was determined using the Fisher's exact test and Kruskall –Wallis H test as appropriate.

Results: We identified 20 cases of biopsy proven BKPyN out of 1031 KTRs (1.9% BKPyN). Of these 20 cases, 5 were early, 10 were florid and 5 were late sclerosing. The change in eGFR (p=0.02) and BK viral load (p=0.03) were associated overall with histologic grade while time from transplant and allograft loss were not. On subgroup analysis of grades of BKPyN, recipients with grade B histology were more likely to have a significant decrease in eGFR compared to those with grade A (p=0.03) while the change from grade B to C was not significant. Although it did not reach statistical significance, grade B and C trended towards having higher BK viral loads at biopsy compared to grade A (p=0.05 and 0.07, respectively).

Conclusion: In our single-center analysis, the histologic severity noted in biopsy-proven BKPyN between grades A and B was significantly associated with an overall worsening of eGFR. Higher BK viral loads trended towards having a worse histologic grade. Interestingly, histologic grade was not associated with eventual graft loss due to BKPyN. The limitations of our study include small sample size and single-center experience. Further studies are needed to confirm our findings and to better optimize BKPyN management to improve overall graft outcomes in KTRs.

CITATION INFORMATION: Swee M, Kuppachi S, Fraer M, Rastogi P, Ten Eyck P, Sanders M. Does Histologic Grade in BK Polyoma Nephropathy Associate with Viral Load, Allograft Dysfunction or Allograft Loss? A Single Center Experience. Am J Transplant. 2017;17 (suppl 3).

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