Acute splenic infarction presenting as an unusual manifestation of essential thrombocythaemia with normal platelet count.

Essential thrombocythaemia (ET) is characterised by elevated platelet count by a clonal stem cell disorder of megakaryocytes. Although thrombosis is a common complication of ET, splenic infarction (SI) is extremely rare. Here, we present the case of a 31-year-old Japanese man who presented with sudden-onset severe pain at the left hypochondrium on the day before admission. Enhanced abdominal CT revealed SI. The laboratory test results revealed a normal platelet count (439×109/L). Subsequently, the patient was diagnosed with ET because the platelet count gradually increased to 50.0×104/µL, and JAK2 V617F mutation was identified. Accordingly, low-dose aspirin was initiated, and no thrombotic episode occurred. Nevertheless, 6 months postdischarge, the platelet count gradually increased to >650 × 109/L, and anagrelide was initiated. This case demonstrates an unusual complication of acute SI due to ET under the rare situation of the normal platelet count.