Abstract
A14-year-old girl with idiopathic nephrotic syndrome showed decoy cells in urine sediments. BK virus is a human polyomavirus that infects nearly 80% of the general population. BK virus is associated with interstitial nephritis and ureteral stenosis in renal allograft recipients. The virus affects tubular epithelial cells that show characteristic intranuclear inclusion bodies. Latent BK virus infection of the renal epithelium is reactivated by immunosuppression, leading to viruria. Inclusion bearing cells sloughed into the urine can be detected in urine cytology. Those cells were named ‘decoy cells’. The detection of decoy cells estimates the likelihood of BK viruria. At the time of the detection of abundant decoy cells, the patient was on prednisolone and cyclophosphamide. We detected BK virus DNA in the urine from this patient by quantitative real-time polymerase chain reaction methods. BK virus DNA excretion disappeared three weeks later without the reduction of immunosuppressive therapy. The results showed that the patient was diagnosed with BK viruria. It is suggested that we need to monitor BK virus nephropathy in pediatric patients receiving immunosuppressive therapy.
