Thrombotic thrombocytopenic purpura: Results of the patients with thrombotic microangiopathies across Japan by ADAMTS13 analysis during 1998–2008

Abstract

Background Thrombotic microangiopathies (TMAs) are pathological conditions, characterized by generalized microvascular occlusion by platelet thrombi, thrombocytopenia, and microangiopathic hemolytic anemia. Two typical phenotypes of TMAs are hemolytic‐uremic syndrome (HUS) and thrombotic thrombocytopenic purpura (TTP). Severe deficiency of plasma ADAMTS13 activity (ADAMTS13:AC) is more specific for TTP but not for HUS.Materials & Methods Since 1998, our laboratory has functioned as a nationwide referral center for TMAs by analyzing ADAMTS13. Of 1564 tested patients from 426 hospitals, 919 were positive for TMAs. Levels of ADAMTS13:AC and the ADAMTS13‐neutralizing autoantibodies (ADAMTS13:INH) in these patients were determined by chromogenic act‐ELISA and/or by classic von Willebrand factor multimer assay.Results TMA patients consisted of two groups, those with severe (less than 3% of normal control) and those with non‐severe deficiency of ADAMTS13:AC. Additionally, both groups were divided into congenital (n = 65) and acquired (n = 854) TMAs. Of the congenital TMA patients, 41 had ADAMTS13:AC deficiency due to gene mutations, while the remaining 24 had the disease of unknown etiology. The 854 patients with acquired TMAs could be largely grouped into three categories: idiopathic TTP (n = 284), idiopathic HUS (n = 106), and secondary TMAs (n = 464). The secondary TMAs were observed in heterogeneous patient groups and were associated with drugs, connective tissue diseases, malignancies, transplantation, pregnancy, E. coli O157:H7 infection, and other factors. All of the patients with acquired severe ADAMTS13:AC deficiency were positive for ADAMTS13:INH.Conclusion Although TMAs are highly heterogeneous pathological conditions, one third of TMA patients have severe deficiency of ADAMTS13:AC. Platelet transfusions to such patients are contraindicated. Thus, rapid ADAMTS13:AC assays will be prerequisite in medical facilities where TMA patients are treated.