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.