Abstract
Thrombocytosis, defined as platelet counts >450 × 10⁹/L, is frequent in the pediatric population and usually secondary to inflammatory conditions or iron deficiency. Essential thrombocythemia (ET), a Philadelphia chromosome-negative myeloproliferative neoplasm, is exceptionally rare in childhood. Pediatric ET often follows an indolent course but carries risks of thrombotic and hemorrhagic events, as well as late progression to myelofibrosis or leukemia. We report the case of a 14-year-old girl presenting with recurrent acral edema, erythema alternating with cyanosis, burning pain, paresthesia, and headaches. Physical examination was unremarkable. Initial suspicion of Raynaud's phenomenon was excluded by nailfold capillaroscopy. Laboratory studies revealed persistent thrombocytosis with platelets over 1,092 × 10⁹/L. Secondary causes were excluded. Bone marrow biopsy revealed megakaryocytic hyperplasia with hyperlobulated megakaryocytes, abdominal ultrasound revealed hepatosplenomegaly, and molecular testing identified a JAK2 V617F mutation, confirming ET. She was initially treated with low-dose acetylsalicylic acid, with partial improvement, but microvascular symptoms persisted, and platelet counts remained >1,000 × 10⁹/L. Hydroxyurea was initiated, leading to progressive platelet reduction and marked clinical benefit. Over three years of follow-up, the patient remained clinically stable, without adverse effects or leukemic transformation. This case illustrates the rarity and diagnostic complexity of pediatric ET, which requires exclusion of reactive causes, bone marrow evaluation, and molecular testing. Management remains particularly challenging due to the absence of pediatric-specific guidelines, with current approaches being largely derived from adult protocols. Cytoreductive therapy may be indicated in cases with extreme thrombocytosis or refractory symptoms, and long-term follow-up is crucial to monitor disease evolution and treatment outcomes. This case highlights the need for multicenter studies and international registries to have pediatric-specific evidence that can better inform diagnostic and therapeutic strategies.