Cytologic appearance of ureteral stenosis caused by polyomavirus

Polyomavirus, BK type (BKV), has emerged as an important cause of allograft failure in renal transplant recipients. It was first described in a renal transplant recipient with an ureteral stricture in 1971.1,2 The use of new immunosuppressive drugs, such as tacrolimus and mycophenolate mofetil, has been associated with a higher risk of reactivation of BKV.3 Viral replication in the urinary tract can be assessed by the presence of \u93decoy cells\u94 on Papanicolaou smears of urinary sediment.4,5 Urinary cytology is thus a rapid method of detecting BK viruria in urine samples. These decoy cells may come from the renal tubular epithelium or from the superficial urothelium.5,6 We report the case of a renal transplant patient who, 1 month after transplantation, had atypical cells in urine, suggesting bladder cancer. A 64-year-old woman underwent renal transplantation after renal failure secondary to chronic renal nephropathy. Five weeks later, urine cytology revealed atypical urothelial cells suggesting malignancy and leading to cystoscopy, which revealed a normal bladder urothelium. When the patient entered the transplantation unit, the antirejection treatment included tacrolimus, prednisolone and mycophenolate mofetil. Cytologic examination of urine in our laboratory (Papanicolaou-stained cytospins) revealed 2 distinct populations of cells within an inflammatory background. There were numerous atypical urothelial cells, sometimes in clusters. Their nuclear/cytoplasmic ratio was increased; the nuclei were irregularly shaped and showed marked hyperchromasia hiding the chromatin pattern (Figure 1). Typical decoy cells were also present (Figure 2). They displayed large, round, homogeneous, basophilic nuclear inclusions occupying nearly the entire nucleus. The inclusions seemed to \u93get out\u94 of the cell. As there was a previous report of atypical cells in the urine, a weekly cytologic examination was recommende