Coombs-positive refractory acquired thrombotic thrombocytopenic purpura in a patient with chronic myelomonocytic leukemia successfully treated with rituximab.

Acquired thrombotic thrombocytopenic purpura (aTTP) is a rare autoimmune disorder characterized by auto-antibodies to Willebrand factor (vWF) cleaving enzyme (ADAMTS13), resulting in unusually large vWF multimers that lead to platelet aggregation, microthrombi formation and microangiopathic hemolytic anemia. Hemolysis in aTTP is mechanical; thus, direct antiglobulin test (Coombs test) is usually negative. Multiple autoimmune conditions and various auto-antibodies have been described in the context of chronic myelomonocytic leukemia (CMML). In this paper, we describe the first case of CMML with auto-antibodies to ADAMTS13, presenting initially as plasmapheresis-refractory Coombs-positive aTTP. Although our patient was not treated for CMML, a complete remission of aTTP was eventually achieved with rituximab. Conclusion; We propose that aTTP should be in the differential diagnosis of CMML patients with thrombocytopenia and anemia (Coombs positive or not) who develop signs of thrombotic microangiopathy. Further studies are much needed to decipher the immune-mediated processes in CMML.