BK virus

  • After renal transplantation, patients are at risk of allograft dysfunction from a wide variety of mechanisms.
  • The biopsy findings here of basophilic intranuclear inclusions are characteristic of BK-virus induced nephropathy.
  • The BK virus is a polyomavirus that is well-known to cause nephritis in renal transplant recipients who are immunosuppressed, with a prevalence of about 5%.
  • Urinalysis in patients with BK-nephritis is consistent with interstitial nephritis, and urine cytology often shows infected cells with an enlarged nucleus and a single basophilic intranuclear inclusion. PCR can be used to identify BK viral DNA in the plasma of patients suspected of having this infection. Diagnosis should be confirmed with an allograft biopsy.
  • Patients may have polyoma BK virus on polymerase chain reaction of the urine or serum or may have polyoma BK virus inclusion-bearing epithelial cells called “decoy cells.”
  • Treatment consists of decreasing the immunosuppression and, in some, antiviral therapy.

A 46-year-old male undergoes a cadaveric kidney transplant for rapidly progressive glomerulonephritis. His past medical history is significant for hepatitis C, hypertension, and type 2 diabetes mellitus. The surgery is uncomplicated, and when he is discharged, his BUN is 12 mg/dL and creatinine is 1.2 mg/dL. His immunosuppression regimen includes cyclosporine, mycophenolate, and low-dose prednisone. Five weeks after the procedure, he complains of malaise. His BUN is 28 mg/dL and creatinine is 2.1 mg/dL. A renal allograft biopsy shows evidence of renal tubular damage with prominent basophilic intranuclear inclusions. Which of the following is the most likely cause of his decreased renal function?