Acquired Amegakaryocytic Thrombocytopenia Presenting as Pancytopenia in a Patient With Chronic Lymphocytic Leukemia: A Case Report.

Acquired amegakaryocytic thrombocytopenia (AAMT) is a rare hematologic disorder characterized by severe thrombocytopenia due to an isolated absence of megakaryocytes in the bone marrow, with preservation of other hematopoietic lineages. We present an 84-year-old man with IgHV-mutated chronic lymphocytic leukemia (CLL), diagnosed in 1997 and managed with observation until initiation of ibrutinib for treatment-naïve CLL in 2024. He presented acutely with pancytopenia, for which a bone marrow biopsy showed marked absence of megakaryocytes. While platelet increments with transfusion were minimal and transient, additional treatments included dexamethasone, IVIG, cyclosporine, thrombopoietin receptor agonists, and reinitiation of ibrutinib. The patient eventually succumbed to gastrointestinal bleeding secondary to severe thrombocytopenia. This case underscores the diagnostic importance of early marrow evaluation in CLL patients with unexplained cytopenia. The pathogenesis of AAMT in CLL is likely multifactorial, involving immune dysregulation and impaired megakaryopoiesis. Management remains challenging due to lack of standardized guidelines and unpredictable treatment responses.