A single-center experience with BK virus nephropathy.

BACKGROUND: BK virus nephropathy has an increasing role in renal transplant dysfunction, since new, highly potent immunosuppressive drugs have been introduced into therapy following renal transplantation. Diagnosis of acute impairment of renal transplant function is complicated by difficulty in differentiating BK virus nephropathy from acute rejection.

PATIENTS AND METHODS: We retrospectively described the findings and therapeutic approaches of 6 consecutive patients with BK virus nephropathy in our transplantation center (75 - 80 transplantations/ year). BK virus nephropathy was classified according to Drachenberg et al. [2004].

RESULTS: We observed an incidence rate of < 1% for BK nephropathy in our center. Four patients had a pattern B whereas 2 patients revealed a pattern C of BK virus nephropathy. Focal C4d-positive staining of peritubular capillaries were found in 2 of the 6 cases. For earlier detection of BK nephropathy, a diagnostic algorithm for each patient after renal transplantation was established. Urine was continuously monitored by cytology for decoy cells and PCR for BK virus DNA. If PCR was also positive for the BK virus in plasma, biopsy of the renal allograft was performed. Thereby diagnosis could be confirmed sooner. For treatment of BK nephropathy in our center, we reduced immunosuppressive agents and initiated a virustatic treatment with cidofovir in the first 3 cases. However, results were not satisfactory and two allografts were lost. We then reconsidered our therapeutic approach and switched the immunosuppressive treatment to leflunomide with consistent low dose steroids. We use therapeutic drug monitoring for leflunomide and aim at a target level of 40 - 100 microg/ml. We lost no allograft with BK nephropathy since using this therapeutic approach.

CONCLUSION: In our center, leflunomide therapy, but not cidofovir, was effective in patients with BK virus nephropathy of the renal allograft.