Two Cases of BK Polyoma Virus Nephropathy in Patients with Isolated Heart Transplantation: Clinical Usefulness of Urinary Cytology

Abstract

<h3>Introduction</h3> BK polyoma virus (BKpV) nephropathy (BKpVN) has been often reported in patients with kidney transplantation, whereas reports regarding BKpVN in patients with heart transplantation (HTx) is still sparse. <h3>Case Report</h3> We recently encountered two patients who developed BKpVN after HTx. Both patients (Case 1 and 2) coincidentally received HTx at the age of 56. A standard triple-drug regimen consisting of tacrolimus, mycophenolate mofetil (MMF), and a corticosteroid was started after surgery and the regimen was converted to everolimus (EVL) with reduced tacrolimus within 6 months after HTx because of donor transmitted atherosclerosis in both patients. Case 1 further underwent percutaneous coronary intervention 3.5 years after HTx. Despite renal-sparing immunosuppresion, values of creatinine begun to increase after HTx in both patients and they were diagnosed with BKpVN through high viral DNA copy number in the urine and blood. Regarding case 1, pathological analysis of kidney biopsy specimens disclosed interstitial infiltrate with lymphocytes associated with tubular injury which also lead to the diagnosis of BKpVN. Retrospectively, both patients were positive for decoy cell within 1 year after HTx therefore, these patients should have been recognized as high risk for BKpVN. After the diagnosis of BKpVN, immunosuppressive regimen of them was further changed to minimum dose of EVL (a trough concentration of 6-7 ng/ml) and MMF (500 mg daily) respectively under the guidance of myocardial biopsy and they have been uneventful for over a year after the diagnosis of BKpVN despite severe chronic kidney disease. <h3>Summary</h3> We presented two rare cases of BKpVN after HTx. In our institution, urinary cytology is regularly examined if there are decoy cells which we think are the sign of over immunosuppression. However, decoy cells detected by urinary cytology also suggest that there is subclinical BKpV infection. Urinary cytology, a noninvasive and cost-effective examination, should be routinely performed for the risk assessment of BKpVN even in HTx patients, since detecting decoy cell would be helpful for the early diagnosis of BKpVN.