Temporal serum creatinine increase and exacerbation of tubulointerstitial inflammation during the first two months in resolving polyomavirus BK nephropathy.

Aim: Polyomavirus BK nephropathy (BKVN) is an important complication in kidney transplantation. After immunosuppressive agents are reduced, some patients experience a temporal increase in serum creatinine (sCr) before viral clearance. The histological characteristics of re-biopsies were therefore investigated to evaluate the time course of remission.

Methods: sCr was measured and urinary cytology evaluated periodically in 14 patients with biopsy-proven BKVN. Remission of BKVN was defined as re-biopsies negative for SV40 large T antigen (SV40-TAg) or for decoy cells on at least three consecutive cytology tests. Early changes in sCr were correlated with re-biopsy findings.

Results: Mean sCr was 1.6 ± 0.6 mg/dL at diagnosis, increasing during the first 2 months to 2.6 ± 2.0 mg/dL, and decreasing thereafter, to 2.3 ± 1.2 mg/dL at 3-4 months. Two patients who experienced further increases in sCr at 3 months showed early graft loss, while the others showed clinical or histological remission. Nineteen re-biopsies were obtained from eight patients over 4 months. Banff i-scores were higher in re-biopsies obtained during the first 2 months than the index biopsies and re-biopsies at 2-4 months (P = 0.02). SV40-TAg positivity was common in re-biopsies during the first 2 months (10/11 biopsies), but rarer at 2-4 months (2/8 biopsies, P = 0.001).

Conclusions: Temporal graft dysfunction and increased inflammation, called immune reconstitution, were observed at 2 months. Later sCr reversal is associated with remission.