A 66-year-old Chinese man was referred for a hematological opinion in 2002 following the incidental discovery of a platelet count of 845 × 109/1 with a normal hemoglobin concentration and white cell count and no splenomegaly. Following bone marrow aspiration and trephine biopsy, a diagnosis of essential thrombocythemia was made. Cytogenetic analysis was normal. JAK2 V617F was detected. The patient was managed with hydroxycarbamide and aspirin. His clinical course was generally uneventful apart from a gastrointestinal hemorrhage in 2010. In 2012, following a period of poor compliance with therapy, he was hospitalized with severe community acquired pneumonia, a cerebral infarct and a platelet count ranging between 415 and 511 × 109 /1.
A blood film showed dysplasia of all granulocyte lineages. Neutrophils were hypogranular and had hypolobated and abnormally shaped nuclei; some had cytoplasmic vacuolation (top left and bottom right). In addition, there were some macropolycytes and these showed dysplastic features such as hypogranularity (top right) and abnormal nuclear forms. All eosinophils were nonlobulated and showed a variable degree of hypogranularity (top left and bottom right). Basophils had reduced granule numbers, giant granules, and irregularly disposed granules (bottom left and right). During the episode of pneumonia, left shift was present (myelocytes, promyelocytes, and blast cells). Following recovery the dysplasia persisted but immature cells were no longer present.
Granulocytic dysplasia is most often recognized in the neutrophil lineage. Eosinophil dysplasia as a feature of a myeloid neoplasm can be difficult to distinguish from the often striking cytological abnormalities in reactive eosinophilia. However, in this patient the uniform lack of lobulation in addition to the variable granule deficiency gave clear evidence of dysplasia. Because of their relative infrequency and the tendency of their granules to dissolve, basophils are not often recognized as dysplastic. However, in this patient all basophils were strikingly abnormal.
The patient now has a platelet count well controlled by hydroxycarbamide but is mildly anemic (Hb 118 g/l). Myelodysplastic evolution in essential thrombocythemia may be prognostically adverse and may be the forerunner of leukemic transformation [1, 2].