Case Of The Month -June 2006

POLYOMAVIRUS IN A URINE

Contents

• Clinical Details
• Cytological Findings
• Histology
• Discussion
• References

Clinical Details

Mr G is a 45-year old male who had a renal transplant twenty-two months previously. His creatinine had increased from 0.08mM to 0.18mM over the preceding six months with decreasing immunosuppression. A fresh voided urine was received comprising 40mls of clear yellow fluid

Cytological Findings

There are occasional epithelial cells showing enlarged nuclei with homogenous intranuclear inclusions and thickened nuclear membranes consistent with decoy cells. Many cells also show non-specific eosinophilic cytoplasmic inclusions.

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Histology

Approximately 50% of the renal tubules showed variable nuclear viral cytopathic effects including granular chromatin with eosinophilic nucleoli, ground glass intranuclear inclusions, and epithelial necrosis with sloughing off. The cells did not stain with HSV or CMV immunostains. PCR was performed and there was significant BK virus DNA present. BK virus has also been detected by PCR in the urine and serum.

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Discussion

Decoy cells were first noted in the 1950’s but only confirmed as having an underlying viral cause in the early 1970’s. The virus was identified as a polyomavirus and the BK strain was first identified in a renal transplant patient in 1971. Polyomavirus is acquired in childhood by the majority of the population. Polyomavirus reactivation occurs following immunosuppression, in AIDS patients, and in diabetics. However, virus reactivation can occur in subjects with no underlying medical condition and virus-infected epithelial cells can be shed for weeks from the urinary tract with the patient remaining clinically well. In the case of renal transplants, BK virus can cause severe renal allograft dysfunction as occurred in this case.

Leopold Koss and Myron Melamed in their text (see reference) describe two stages of recognisable viral infection in the urinary sediment: inclusion and post-inclusion stages. Basophilic inclusions and pale inclusions have been described in the inclusion stage, the former typically a single dense basophilic homogenous intranuclear inclusion, and the latter are inclusions with a transplant clear space within the nucleus. The post-inclusion stage is where there has been leaching of the virus and the nucleus appears empty with a residual network of chromatin filaments

Reference

1. L.D.G. Koss and M.R. Melamed, Koss’s Diagnostic Cytology and its histopathological basis, 5th edn, Lippincott Williams & Wilkins.

Thanks to Judy and the team for submitting this case