Essential thrombocythemia in children and adolescents — analysis of 31 cases

Introduction. Essential thrombocythemia is an extremely rare disorder in childhood. This disease is characterized by a persistent increase in the peripheral blood platelet count, associated with a proliferation of atypical megakaryocytes in the bone marrow.Aim — to analyze the clinical features of the course of essential thrombocythemia (ET) and the response to therapy in pediatric and adolescent patientsMaterials and methods. Thirty-one patients with ET under the age of 21 years were analyzed. All patients were diagnosed with ET in accordance with WHO criteria on the basis of an examination, including assessment of clinical data, laboratory tests (general clinical tests; morphological, genetic, and histological examinations of bone marrow), instrumental studies, and an assessment of response to treatment.Results. The average age of disease onset was 9 years 9 months, with a median of 9 years 6 months. Organomegaly was recorded in 16 (52 %) patients, of whom 6 (37.5 %) had isolated splenomegaly and 6 (37.5 %) had hepatosplenomegaly. Bleeding was noted in 6 (19.4 %) patients with a deep decrease in vWF:RCo (no more than 15 %) and an extreme increase in platelets (PLT) (more than 2000 × 109 /L). Twelve (38.7 %) patients suffered from microcirculation disorders (headaches, dizziness, melalgia), half of them had a platelet count of 1000–2000 × 109 /L, which is comparable to asymptomatic patients. No thrombosis was registered in our group. The JAK2V617F mutation was detected in 3 (9.7 %) patients, a mutation in the CALR gene was found in 9 (29.0 %) of patients, there was a mutation in the MPL gene in one (3.2 %) patient, and in the remaining cases (18 (58.1 %) patients), there was no damage to typical driver genes. Translocation t(12;12) was revealed in 1 (3.2 %) patient. The response to one-component cytoreductive therapy (CR+PR) was found to be quite high in young patients and constituted about 70–80 %. The complete response rate (CR) was as follows, respectively: 42.9 % (3) — to anagrelide therapy (ANA), 47.4 % (9) — to interferon therapy (INF), and 0 % — to hydroxycarbamide (HU). However, HU was not used in the fi rst line of therapy for the children in our group.Conclusion. In the pediatric population, ET patients are dominated by the group of “triple-negative” disease, which somewhat complicates the differential diagnosis with secondary thrombocytosis. Compared to the adult population, the risk of bleeding is higher for pediatric patients, which is associated with the large number of patients with extremely high levels of platelets. In the case of hemorrhagic syndrome development or microcirculatory disorders that cannot be stopped by taking antiplatelet agents, we recommend giving preference to INF and HU as fi rst-line therapy, due to the peculiarities of pharmacokinetics and the potential risk of progression of myelofi brosis during ANA therapy.