IntroductionThis month we have an interesting case kindly submitted by Sarla Naran , from Wellington Hospital. |
A 39 year old male with history of renal transplant due to end stage renal failure secondary to mesangiocapillary glomerulonephritis presented with the persistent rise in the serum creatinine. The urine sample from this patient was sent for cytologic examination.
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The papanicolou stained filter preparation showed a large number of dissociate cells with enlarged hyperchromatic nuclei of variable size. Some had degenerative changes. Some had large pale basophilic inclusion that occupied almost the entire volume of the enlarged nucleus surrounded by rim of chromatin and had a ground glass appearance. In addition, some inflammatory cells and considerable cell debris were seen in the background.
The characteristic morphologic features of decoy cells along with history of renal transplant in the patient, the diagnosis of human polyoma virus (BKV) infection was made and supported by positive serum test.
A renal allograft biopsy showed tubular cells with inclusions consistent with Polyoma Virus infection. BK virus infection was confirmed by PCR (Polymerase Chain Reaction) and serum test.
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Polyoma Virus (PV) infection is frequent in renal transplant patients. BK virus and JC virus are human polyoma virus that infect a large number of people after primary exposure, the virus become latent and their genomic sequences can be detected only by PCR in kidney and urinary tract tissue and brain tissue (JCV).
BK virus reactivation in the renal parenchyma cause tubulointerstitial nephropathy almost exclusively in renal allograft recipients (immunosuppresed). The diagnostic gold standard for PVN (polyoma virus nephropathy) is the morphologic and immuno histochemical demonstration of PV infection and damage to epithelial cells in renal biopsy.
When BKV is reactivated under immunosuppression, it proliferates within the nuclei of urothelial and tubular cells, produces characteristic viral inclusion bodies. These cells in voided urine are called “Decoy cell”.
Periodical assessment of urine and serum sample from renal transplant patients by PCR and morphologic (cytologic) method is mandatory for follow up. The presence of decoy cells in urine sample represent active PV infection which is associated with the severity of immunosuppression.
The morphology of the BK viral inclusion is typical however in rare cases the Adeno virus, the Herpes Simplex virus, JC virus may cause similar changes which can be distinguished on PCR. It is important to distinguish malignant cells from decoy cells in urine, the former having nuclei with coarse chromatin which contrast with the structureless nuclei of the decoy cells. Cytologic analysis of the urine is an important diagnostic tool for screening and follow up of renal transplant patients at risk of PVN. It is simple and safe method to identify viral nephropathy.
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Thanks to Sarla for submitting this case