Anti-c-Mpl (thrombopoietin receptor) autoantibody-induced amegakaryocytic thrombocytopenia in a patient with systemic sclerosis

Amegakaryocytic thrombocytopenia (AMT) associated with systemic sclerosis (SSc) has been described in several case reports, but the underlying mechanisms have not been identified. Here we describe a rare case of SSc accompanied by thrombocytopenia and megakaryocytic hypoplasia, in which autoantibody against thrombopoietin receptor (c-Mpl) was detected. A 61-year-old woman with limited SSc was admitted to our hospital because of severe thrombocytopenia (platelet count 0.2 × 10⁴/mm³) with gingival bleeding. Her bone marrow was hypocellular with absent megakaryocytes, consistent with AMT. Treatment with corticosteroids and intravenous immunoglobulin infusions resulted in an increased platelet count, and she sustained a remission over a 1-year period, with a platelet count averaging 10.0 × 10⁴/mm³. Her serum was strongly positive for antic-Mpl antibody, and IgG fraction purified from her serum inhibited thrombopoietin-dependent cell proliferation in vitro. Our case report suggests that AMT in patients with SSc could be mediated by the anti-c-Mpl antibody, which functionally blocks an interaction between thrombopoietin and c-Mpl.