Hemorrhagic cystitis (HC) is a serious complication after hematopoietic stem cell transplantation (HSCT). The pathogenesis of HC in adults is not fully understood and may be influenced by BK virus infection, type of transplant, conditioning regimen, stem cell source, and graft-versus-host disease. Little is known about the development of HC in children after HCST, especially about the association with BK virus infection. Therefore, we retrospectively analyzed the incidence, risk factors and BK virus association of HC in 165 consecutive children (median age, 12 years) who underwent peripheral blood stem cell (n=97; T-cell depleted: n=48) or bone marrow transplantation (n=68) between 1/2000 and 12/2006 in a single center. Fifty nine patients received autologous HSCT and 106 patients underwent allogeneic HSCT. Nineteen of the 165 patients (11.5%) developed HC after a median of 33 days (range, 1–98 days). All 19 patients with HC underwent allogeneic HSCT and showed BK viruria after transplantation. An acute graft-versus-host disease was significantly more frequent in children with HC (P < .001). Significant risk factors in univariate binary logistic analyses were age > 12 years (OR, 3.275; P < .031), use of busulfan (OR, 3.514; P < .013), use of busulfan and cyclophosphamide in combination (OR, 4.935; P < .002), and an unrelated donor (OR, 3.309; P < .043). Independent risk factors in multivariate binary logistic analyses were age > 12 years and the combination of busulfan and cyclophosphamide. We suggest that cyclophosphamide is toxic to the urinary bladder and busulfan enhances this effect. Furthermore, we analyzed the BK virus load in urine by real-time polymerase chain reaction. We found in patients without HC a significantly increased number of BK virus copies in urine in children older than 12 years (P < .009) and in children who received antithymocyte globulin (P < .001). In addition, BK virus load in urine was significantly increased in children who suffered from HC. Thirteen of 14 children with HC had a BK virus load in urine >107 copies/mL (P < .001). We observed in individual BK virus profiles an increase of BK virus copies in urine before the onset of HC. We conclude that HC in children is a disease of multiple etiologies. Allogeneic HSCT, the combination of busulfan and cyclophosphamide, age > 12 years, and an unrelated donor are risk factors for the development of HC in childhood. Increased BK virus load in urine of more than 107 copies/mL may lead to HC. Therefore, it is useful to quantify BK virus in urine in those children with above mentioned risk factors to initiate early treatment or to prevent the development of HC.

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