Essential thrombocythemia (ET) is a chronic myeloproliferative neoplasm that involves primarily the megakaryocytic lineage. After many years, a few patients with ET may develop bone marrow (BM) fibrosis and rarely develop osteosclerosis. A 60-yr-old female was admitted due to severe left upper quadrant abdominal discomfort. She had been diagnosed as ET 19 yrs ago. On liver computed tomography severe splenomegaly was shown. Laboratory tests revealed WBC 24.3×10⁹/L, hemoglobin 13.4 g/dL, platelets 432×10⁹/L, lactate dehydrogenase 4,065 IU/L (reference range; 240-480). Blood smear demonstrated leukoerythroblastosis, teardrop cells, and giant and hypogranular platelets. BM study revealed inadequate aspirate due to dry tap. BM biopsy showed clusters of dysplastic megakaryocytes, grade 3 fibrosis, and severe osteosclerosis. Major/minor BCR-ABL1 rearrangement and JAK2 V617F mutation were not detected. Cytogenetic studies revealed normal karyotype. According to the 2008 WHO diagnostic criteria, the patient was diagnosed as having post-essential thrombocythemia myelofibrosis with severe osteosclerosis.

Keywords: Essential thrombocythemia, Myelofibrosis, Osteosclerosis