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Clinical and histological characteristics of livedo racemosa in essential thrombocythemia: A report of two cases and review of the published works

Essential thrombocythemia (ET) is a rare clonal myeloproliferative disorder with a prevalence rate of approximately 1–3 cases per 100 000 individuals per year. ET is characterized by a persistent increase in the platelet count with hyperplasia of bone marrow megakaryocytes. It is difficult to make a diagnosis of ET, because most thrombocythemia are reactive to certain disease conditions including iron deficiency anemia, infection, collagen diseases and malignant tumors. Mutation in the Janus kinase (JAK)2 gene is present in approximately 50–70% of ET patients, and somatic mutations in the calreticulin (CALR) gene were recently discovered in approximately 20–25% of sporadic patients with ET or primary myelofibrosis. Various cutaneous manifestations of ET often occur by microvascular thrombosis and precede severe arterial and venous thromboembolic events in other organs. Therefore, in order to prevent such severe events, it is important to make an early diagnosis of ET based on a number of cutaneous manifestations. Here, we report two cases of ET diagnosed based on livedo racemosa on feet with gene mutations in JAK2 and CALR, respectively, and show the pathological and immunohistological findings of the livedo resulting from platelet thrombosis rather than vasculitis. We also review the cutaneous manifestations in current published reports of Japanese ET patients. Our patients were successfully treated with low‐dose aspirin, a vasodepressor and hydroxyurea, following regressed livedo and reduced platelet counts.