Extreme essential thrombocytosis in a healthy asymptomatic 6-month-old child

In healthy child essential thrombocytosis is always an incidental finding during routine check. Essential thrombocytosis (primary thrombocythemia) is a non-reactive, chronic myeloproliferative disorder in which sustained megakaryocyte proliferation leads to an increase in the number of circulating platelets, on the other hand reactive or secondary thrombocytosis is the more common form, with infectious diseases being the most common cause. Mutations in Janus kinase 2 (JAK2), calreticulin (CALR), or myeloproliferative leukemia (MPL) are found in approximately 90% of patients with essential thrombocytosis. We describe a case of extreme thrombocytosis in a healthy 6-month child. She required admission for workup (maximum number of platelets 1900,000/mm3). With this case, we reviewed the different causes of thrombocytosis in childhood, differential diagnosis, World Health Organization (WHO) criteria for diagnosis of essential thrombocytosis, and the available treatments in case of extreme thrombocytosis.