Diagnosis and management of BK polyomavirus interstitial nephritis in renal transplant recipients

Background. Interstitial nephritis caused by BK polyomavirus is a recognized complication of renal transplantation. A study of renal transplant recipients at Duke University Medical Center was undertaken to evaluate diagnostic modalities and assess clinical outcomes in transplant polyomavirus infections. Methods Polyomavirus nephritis was identified in 6 of 240 patients who received renal transplants between January 1996 and June 1998 and an additional patient who underwent transplantation in 1995. The clinical records of these seven patients were reviewed, as were all renal biopsy and nephrectomy specimens. Electron microscopy (EM) was performed on negatively stained urine samples from 6 patients with polyomavirus infection and 23 patients with other diagnoses. Results. Patients with polyomavirus infection shared several clinical features, including ureteral obstruction (5/7 patients), lymphocele (3/7), bacterial urinary tract infection (3/7), hematuria (3/7), cytomegalovirus infection (3/7), and immunosuppression with mycophenolate mofetil (6/7). All patients experienced elevations in serum creatinine, which stabilized or decreased in four patients with altered or decreased immunosuppression. The diagnosis of polyomavirus infection was established by renal biopsy and EM of urine in five patients, by biopsy alone in one, and by EM alone in one. Sequential examinations of urine by EM were used to monitor the course of infection in six patients. Conclusions. Interstitial nephritis due to BK polyomavirus occurred in 2.5% of patients receiving renal transplants at our center since 1996. Polyomavirus infection can cause transplant dysfunction and graft loss, but progression of the infection can frequently be abrogated with alterations in immunosuppressive therapy. Both renal biopsy and EM of urine samples are useful in the diagnosis and monitoring of polyomavirus infections.