Biopsy-Proven BK Virus-Associated Nephropathy: Clinico-Pathologic Correlations

Objectives: Our objective was to study the clinicopathologic correlations in BK virus nephropathy. Materials and Methods: We conducted a retrospective study of all patients with biopsy-proven polyoma (BK) virus infection. We compared their survival and renal outcomes versus BK virus-negative patients with biopsyproven graft rejection. Histopathologic charac terization by a blinded nephropathologist was performed. Results: BK nephropathy was found in 10 patients biopsied for graft dysfunction. All virus-positive patients received antithymocyte globulin induction therapy compared with only 59.3% of the BK-negative group (P =.06). The percentage of patients in the BK-negative group who received acyclovir was significantly higher than that in the BK-positive group (P =.01). After a mean observation period of 6.8 +/- 3.2 years, 70% of the BK group had functioning grafts compared with 68% in the BK-negative group (P =.9) with similar 3- year graft survival in the 2 groups (80% and 90%; P =.8). Within the BK group, graft survival was better in the older group (P =.005) and in those with deceased donor kidney grafts (P =.016). Patients in the BK-negative group were heavier (mean weight of 64.3 +/- 12.1 vs 46.7 +/- 20.6 kg; P =.003). None of the histopathologic features studied had any effect on renal prognosis. Conclusions: The risk factors for developing BK neph ropathy were use of antithymocyte globulin, lower weight, and not using acyclovir as early prophylaxis. Within the BK nephropathy group, better graft survival was observed in deceased donor kidney recipients and in older patients. The viral load and polyoma virus nephropathy stage did not affect graft survival in this small sample study.