Decoy cells

Polyoma BK viral disease, in which decoy cells are detectable, was first described in 1971 in a kidney transplant patient. The name of the disease is derived from the first letters of the patient's name, in which the virus could be detected at that time (Hahn 2009).

Decoy cells are the occurrence of urothelial and/or tubule cells in urine that are infected with the Polyoma virus (Neuendorf 2018).

Decoy cells occur in the context of a polyoma viral disease caused by BK or JC viruses.

Between 75 % - 100 % of the world population have antibodies against BK and JC viruses (Hahn 2009).

Only in immunocompromised persons, e.g. after a (kidney) transplantation, in HIV patients, patients with systemic lupus erythematosus, malignant tumours etc. the Polyoma virus leads to a disease in which the virus can be detected in urine (Doer 2010).

Decoy cells occur, for example, in 4 % - 8 % of kidney transplant patients (Doer 2010). I do not have any figures on other transplanted or immunocompromised patients.

The disease usually progresses subclinically. However, the following symptoms may also exist, such as:

• slight infections of the respiratory tract
• Nephritis
• hemorrhagic cystitis (mainly in bone marrow transplant recipients)
• Cystitis (mainly in children)
• very rare are a
  • subacute meningitis
  • interstitial pneumonia (Hahn 2009)

The detection of decoy cells is only possible in specialized laboratories, otherwise the high sensitivity cannot be achieved (Kuhlmann 2015). The prerequisite for the detection is a fresh (< 2 h old) urine sample (Rathert 2018).

A kidney biopsy may be required for further diagnosis (Herold 2020).

Microscopically, the decoy cells are:

• Epithelial cells with
  • enlarged nuclei
  • intranuclear virus inclusions (Herold 2020)

Decoy cells can easily be confused with atypical cells (hence the name "decoy").

Likewise, confusion with old leukocytes / renal epithelia in non fresh urine is possible (Neuendorf 2018).

Any existing immunosuppression in patients with decoy cells should be reduced as far as reasonable.

In non-immunosuppressed patients or after unsuccessful reduction of the immunosuppressive drugs administered so far, treatment with the immunosuppressive drug Leflunomide can be attempted (Doer 2010).

Dosage recommendation: Leflunomid is usually used for rheumatic diseases. In this case 100 mg are given initially over 3 days, followed by 10 mg - 20 mg / d (Rietbrock 2013).

An effective antiviral treatment is not yet known (Herold 2020), in older writings a treatment attempt with the antiviral drug cidofovir (Cave: nephrotoxic) is recommended (Doerr 2010).

Kidney transplanted patients with polyoma virus nephropathy lose the transplant in up to 80% of cases (Herold 2020).

1. Doer H W et al. (2010) Medical Virology: Basics, Diagnosis, Prevention and Therapy of Viral Diseases.Georg Thieme Verlag 248
2. Hahn H et al (2009) Medical Microbiology and Infectiology Springer Verlag 546
3. Herold G et al (2020) Internal medicine. Herold Publishing House 648
4. Kuhlmann U et al (2015) Nephrology: Pathophysiology - Clinic - Kidney replacement procedure. Thieme Publishing House 794
5. Neuendorf J (2018) The urine sediment: microscopy, pre-analysis, evaluation and reporting. Springer publishing house 35
6. Rathert P et al (2018) Urine Cytology and Sediment Analysis: Practice and Atlas. Springer publishing house 196
7. Rietbrock N et al (2013) Clinical pharmacology: drug therapy. Steinkopff Publishing House Darmstadt 544