Acute ST-segment Elevation Myocardial Infarction as the First Manifestation of Essential Thrombocytosis.

A 36-year-old female with no significant past medical history presented with sudden onset of crushing substernal chest pain. When the emergency medical services (EMS) arrived, she had a cardiac arrest requiring defibrillation two times in the field prior to arriving at the hospital. In the emergency department (ED), the electrocardiogram (ECG) was significant for ST-elevation that suggested acute anterolateral infarct. Her laboratory evaluation also showed a platelet count of 1095 x 103/ul. Also, her troponin levels were at 0.16 ng/ml at the time of arrival and peaked at 42.8 ng/ml. She immediately underwent a cardiac catheterization which showed 100% occlusion of her left anterior descending (LAD) artery by a thrombus, which was then treated with a thrombectomy and a single drug-eluting stent was placed. Upon further work-up of her thrombocytosis, the patient had a bone marrow biopsy showing megakaryocytic hyperplasia which no evidence of fibrosis. She was tested for Janus kinase 2 (JAK2) mutation which was positive. The patient was diagnosed with essential thrombocytosis (ET) and was started on cytoreduction therapy with hydroxyurea. Her platelet counts responded appropriately and dropped to less than 500 x 103 at the time of discharge.