Brière Jean
Hématologie, Hôpital d'Argenteuil, 97105 cedex.
Bull Acad Natl Med. 2007 Mar;191(3):535-48.
An increased platelet number in blood depends on a limited spectrum of causes, which aren't always simple to identify. Secondary thrombocytosis is a reactive process in relation with acute or chronic inflammatory diseases, or asplenia. The infrequent inherited thrombocytoses disorders are suspected when similar cases are observed in the same family. However, the most frequent causes of chronic thrombocytosis in adults are the so-called chronic myeloproliferative syndromes (chronic myelocytic leukaemia, polycythemia vera, primary myelofibrosis, essential thrombocytemia), and to a lesser extent, myelodysplastic syndromes. In the course of these disorders, thrombocytosis is often the first recognized abnormality. Chronic myelocytic leukaemia is easily diagnosed owing to the presence of either the Philadelphia chromosome or the BCR-ABL fusion gene product. The next step still relies upon a distinction according to the PVSG or the WHO criteria of Polycythemia Vera (PV) and Idiopathic myelo fibrosis (IMF) to finally confirm genuine Essential Thrombocythemia (ET). The recent description of the V617F mutation of JAK2 in 90% of PV patients, 43 to 67% with IMF and 50% of ET diagnosed according to either the PVSG or the WHO criteria is a definite characteristic of clonality now accessible in haematology practice. However, this mutation is neither specific nor constant in any of the Philadelphia negative myeloproliferative disorders, which outlines the importance of the WHO criteria of megakaryocytic abnormalities on bone marrow biopsy as the hallmark of Ph negative MPDs. The exclusion of PV and of IMF, including pre fibrotic and early fibrotic forms is still required for the diagnosis of "true" ET. Disease stratification and treatment strategy are targeted on the evaluation and prevention of vascular complications. Acute leukaemia or myelodysplasia, and other clonal progressions like myelofibrotic transformation, are infrequent and delayed events. However, according to the present data, the risk of fibrotic progression or of leukaemic transformation is not related to the mutation status of ET patients.
血液中血小板数量增加的原因有限，且并不总是易于识别。继发性血小板增多症是一种与急性或慢性炎症性疾病或无脾症相关的反应性过程。当在同一家族中观察到类似病例时，怀疑存在罕见的遗传性血小板增多症。然而，成人慢性血小板增多症最常见的原因是所谓的慢性骨髓增殖性综合征（慢性粒细胞白血病、真性红细胞增多症、原发性骨髓纤维化、原发性血小板增多症），其次是骨髓增生异常综合征。在这些疾病过程中，血小板增多症往往是首先被识别的异常情况。由于存在费城染色体或BCR-ABL融合基因产物，慢性粒细胞白血病很容易诊断。下一步仍需根据真性红细胞增多症（PV）和特发性骨髓纤维化（IMF）的PVSG或WHO标准进行区分，以最终确诊真正的原发性血小板增多症（ET）。最近在90%的PV患者、43%至67%的IMF患者以及根据PVSG或WHO标准诊断的50%的ET患者中发现了JAK2的V617F突变，这是血液学实践中目前可检测到的克隆性的明确特征。然而，这种突变在任何费城阴性骨髓增殖性疾病中都既不特异也不恒定，这凸显了WHO关于骨髓活检中巨核细胞异常标准作为费城阴性MPD标志的重要性。诊断“真正的”ET仍需排除PV和IMF，包括纤维化前期和早期纤维化形式。疾病分层和治疗策略旨在评估和预防血管并发症。急性白血病或骨髓发育异常以及其他克隆进展，如骨髓纤维化转化，并不常见且发生较晚。然而，根据目前的数据，纤维化进展或白血病转化的风险与ET患者的突变状态无关。
