MEDizzy - A 67-year-old woman with a 5-year history of hypertension

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Blood and Immune Systems

A 67-year-old woman with a 5-year history of hypertension has suffered from palmar erythema and facial flushing associated with pruritus (itching) for several years. She has undergone phlebotomy for erythrocytosis on multiple occasions; however, erythrocytosis persists (red blood cells 7 million/μL, hemoglobin 18.9 g/dL, hemocrit 57.7%). She was transferred to the hematology department. Splenomegaly, low plasma erythropoietin (EPO), and a positive genetic test for the JAK2 mutation confirmed a diagnosis of polycythemia vera. A bone marrow biopsy would most likely reveal which of the following findings?

ExplanationIn polycythemia vera, a mutation in the JAK2 gene causes uncontrolled proliferation of the myeloid stem cells, resulting in hyperplasia of the erythroid (red blood cell), granulocytic (white blood cell), and megakaryocytic (platelet) cell lines. This results in increased red blood cell mass, leading to a variety of problems, including hypertension and flushing. The high RBC mass also inhibits erythropoietin (EPO) release, because oxygen delivery is adequate. The myeloid stem cells also stimulate production of mast cells, which release histamine; this is responsible for the patient’s pruritus.