What is the most likely diagnosis?

C. Peripheral blood smear reveals severe thrombocytopenia, with no abnormalities in leu kocytes and RBCs. Failue ofiTP to respond to corticosteroid therapy is usually considered an indica tion to perform bone marrow evaluation to rule out other pathology. Bone marrow aspirate and biopsy reveal absence of megakaryocytes, a finding not consistent with the diagnosis ofiTP. This presentation is most consistent with acquired AMT, a condition characterized by the presence of pathologic auto antibodies directed at thrombopoietin receptor. Acquired AMT has been associated with other auto immune conditions and large granular lymphocyte leukemia (LGL). Bone marrow biopsy and otherwise normal peripheral blood counts do not support the diagnosis of AA. There is no peripheral blood features or any evidence of marrow fibrosis that would be expected in cases of MF or AMKL. Treatment includes immunosuppression with cyclosporine, antithymocyte globulin, rituximab, or the use of thrombopoietin (TPO) agonist. Allogeneic hematopoietic stem cell transplantation has been used in few cases with durable responses (Arthritis Rheum. 2002;46(8):2148, Arthritis Rheum 2003;48(6):1647, Am l Hematol. 1999;62(2):115, Am J Hematol. 2007;82(7):650, Clin Adv Hematol Oneal. 2010;8(11):806, Bone Marrow Transplant. 1999;24(12):1337).