[Latent essential thrombocythemia becoming perceptible after splenectomy]

A 47-year-old male was admitted to our hospital because of left hypochondrium part pain and was diagnosed with splenomegaly with splenic infarctions in May 2016. His complete blood cell count was almost within normal limits, and a bone marrow biopsy revealed normal cellularity with no fibrosis. In addition, no abnormal uptake was noted on FDG PET/CT. In August 2016, he underwent splenectomy for splenomegaly. The histological examination revealed fibrotic stenosis of the blood vessels in the spleen. After splenectomy, his platelet count elevated and remained at >1,000×10⁹/l 3 months later. Finally, he was diagnosed with latent essential thrombocythemia (ET) because the JAK2V617F mutation was positive. Accordingly, oral hydroxyurea was initiated. Thrombosis could be a complication in myeloproliferative neoplasms (MPN). In our case, ET was masked, perhaps, because of hypersplenism and splenomegaly because of splenic vein thrombosis. Hence, examination of the JAK2V617F mutation in patients with splanchnic vein thrombosis is recommended because of the possibility of latent MPN.