RESUMEN

Myeloproliferative neoplasms (MPN), which include primary myelofibrosis (PMF) and essential thrombocytopenia (ET), are characterized by the clonal proliferation of mature blood cells as a result of the overactivation of the JAK/STAT pathway. Extramedullary hematopoiesis (EMH), a common complication of PMF, occurs due to the dysregulation of the bone marrow microenvironment. We report an interesting case of a 73-year-old female with a working diagnosis of ET who was found to have EMH in the liver on biopsy after she had newly onset elevated liver enzymes and her ET had progressed to secondary myelofibrosis. We conclude that in patients with MPN who have rising liver enzymes, EMH in the liver should be part of the differential diagnosis. In addition, we believe that EMH is a sign of progression from MPN to secondary myelofibrosis and that it is imperative for performing bone marrow aspiration and biopsy in order to reassess hematopoiesis and to look for bone marrow fibrosis as well as evidence of progression.