Influenza-associated thrombotic microangiopathy with unbalanced von Willebrand factor and a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 levels in a heterozygous protein S-deficient boy.

Influenza infections often cause pneumonia, but there is limited information on thrombotic microangiopathy (TMA) in these circumstances. We report the case of an 11-year-old boy who developed TMA during the acute phase of H1N1 influenza. Plasma von Willebrand factor (VWF) was elevated, whereas a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13 (ADAMTS13) activity was mildly reduced in the absence of ADAMTS13-neutralizing autoantibody, resulting in low ratio of ADAMTS13 to VWF. The patient was treated intensively, including plasma exchange, and he recovered from the TMA. He developed pulmonary embolism (PE), however, after removal of the central venous catheter. The findings suggested that influenza-associated cytokines enhanced the release of unusually large VWF multimers from vascular endothelial cells and promoted the formation of platelet thrombi and TMA. Subsequent analysis further indicated the presence of familial protein S deficiency, and it seemed likely that the PE was more related to this heterozygous protein S defect.