Agnogenic Myeloid Metaplasia

A set of clinical and pathological criteria for the diagnosis and staging of Philadelphia chromosome-negative myeloproliferative disorders (Ph(1-)-MPDs) is presented by including bone marrow histopathology as a significant tool to identify the early, manifest, and advanced stages of essential thrombocythemia (ET), polycythemia vera (PV), and idiopathic myelofibrosis/agnogenic myeloid metaplasia (IMF/AMM). This combined approach provides a pathognomonic clue to each of the different subtypes of Ph(1-)-MPDs and further enables recognition of the various steps in the evolution of the myeloproliferative process Increase and clustering of giant to large megakaryocytes with mature cytoplasm and multilobulated staghorn-like nuclei in a normal or only slightly increased cellular bone marrow represent major hallmarks of ET. Loose assemblies of small to giant pleiomorphic megakaryocytes containing deeply lobulated nuclei together with a proliferation of erythro- and granulopoiesis (panmyelosis) are the specific lesions of PV. The initial prefibrotic and the overt and more advanced myelofibrotic stages of IMF/AMM show a pronounced proliferation of an abnormal megakaryo- and granulopoiesis dominated by clustered atypical medium-sized to giant megakaryocytes with cloud-like, bulbous, and often hyperchromatic nuclei, which are not seen in allied subtypes of MPDs including chronic myeloid leukemia (Ph(1+)-CML) and myelodysplastic syndromes (MDS). The presented clinical and pathological criteria modify the Polycythemia Vera Study Group (PVSG) proposals for the Ph(1-)-MPDs by including bone marrow histopathology and are in keeping with features outlined in the new World Health Organization classification. The latter allows the differentiation of true ET from reactive thrombocytosis and from thrombocythemias as an eventually presenting finding in PV, IMF/AMM, MDS, and Ph(1+)-CML. Moreover, these diagnostic guidelines are able to separate latent and early PV from secondary erythrocytosis and to detect the prefibrotic and early stages of IMF/AMM. Myelofibrosis is not a feature of ET and is rarely observed in PV at time of diagnosis, but it becomes apparent during long-term follow-up and constitutes a prominent lesion during the course of IMF/ AMM. Life expectancy is almost normal in ET and is also not significantly altered during the first, but compromised during the second, decade of follow-up in PV. On the other hand, survival is substantially shortened in IMF/AMM, even for patients with thrombocythemia as a frequent finding of prefibrotic and early stage IMF/AMM.

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Clinical and morphological criteria for the diagnosis of prefibrotic idiopathic (primary) myelofibrosis

Thiele

Kvasnicka

Zankovich

et al. 2001

Ann Hematol

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A clinicopathological study was performed to define initial-prefibrotic precursor stages of idiopathic (primary) myelofibrosis (IMF) by presenting laboratory and histological bone marrow features. Contrary to the usually accepted diagnostic requirements for IMF, including bone marrow fibrosis and a leukoerythroblastic blood picture, we found that 80 patients did not completely comply with these criteria. In particular, this cohort displayed no increase in the reticulin-collagen fiber content of the bone marrow at onset. Therefore, these cases were occasionally regarded as unclassifiable chronic myeloproliferative disorders (MPDs), or presumptively as essential thrombocythemia (ET). Patients were characterized by a certain set of clinical parameters comprising a borderline to slight leukocytosis and therapy-refractory anemia, minimal to modest splenomegaly, and often an elevated platelet count. Peripheral blood films revealed, only very sparsely, tear drop cells and a few erythroid and myeloid precursors, but no definite leukoerythroblastic reaction. Bone marrow histopathology was consistent with an increase in cellularity and a prominent left-shifted neutrophil granulopoiesis. Erythropoiesis disclosed a slight reduction with small to medium-sized islets. Megakaryopoiesis was the most prominent diagnostic hallmark to distinguish initial-prefibrotic IMF from the allied subtypes of MPDs. This cell lineage was not only characterized by a conspicuous growth and abnormal clustering, but also by a pronounced deviation from nuclear-cytoplasmic differentiation (dysplastic appearance). Cytological anomalies were compatible with a large variety of size and shape, ranging from giant- to atypical micromegakaryocytes with compact and bulky, cloud-like nuclei, due to a coarse lobulation and a frequent occurrence of naked (denuded) nuclei. Follow-up examinations, including sequential trephine biopsies in 22 patients, revealed a transition into myelofibrosis accompanied by laboratory findings in keeping with manifest IMF. In conclusion, morphological and clinical parameters have been validated by this study, which are consistent with a set of diagnostic criteria to recognize initial or prefibrotic precursor stages of IMF.

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Agnogenic Myeloid Metaplasia

Cited by 10 publications

References 27 publications

Myeloproliferative Syndromes and Thrombocythemia

Myeloproliferative Syndromes and Thrombocythemia

Clinical and Pathological Criteria for the Diagnosis of Essential Thrombocythemia, Polycythemia Vera, and Idiopathic Myelofibrosis (Agnogenic Myeloid Metaplasia)

Clinical and morphological criteria for the diagnosis of prefibrotic idiopathic (primary) myelofibrosis

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