Hematopoietic stem cell transplantation-associated thrombotic microangiopathy accompanied by renal arteriolar C4d deposition.

HSCT-associated thrombotic microangiopathy (TA-TMA) is a severe complication with a poor prognosis. Recently, it has been reported that complement system dysregulation, such as CFH autoantibodies and deletions CFH-related genes 3 and 1, induced TA-TMA. In addition, C4d-positive renal arterioles are both a good marker of complement system activation and a useful diagnostic tool for TA-TMA. Because dysregulation of the complement system is associated with TA-TMA, the complement system might be a therapeutic target, such as eculizumab, a terminal complement inhibitor. Herein, we describe an eight-yr-old boy who developed TA-TMA accompanied by severe renal dysfunction. His renal specimen showed diffuse C4d deposition in the renal arterioles, which is consistent with TA-TMA. Although the patient gradually improved without eculizumab, renal arteriolar C4d staining in sample with TA-TMA shows the complement system activation and may guide the target therapy using the eculizumab.