DIAGNOSTIC-CRITERIA OF THE MYELOPROLIFERATIVE DISORDERS (MPD) - ESSENTIAL THROMBOCYTHEMIA, POLYCYTHEMIA-VERA AND CHRONIC MEGAKARYOCYTIC GRANULOCYTIC METAPLASIA

Philadelphia chromosome-positive essential thrombocythaemia (Ph+-ET) a nd chronic granulocytic leukaemia (Ph+-CGL) constitute a separate mali gnant disease entity, whereas essential thrombocythaemia (ET), polycyt haemia vera (PV) and chronic megakaryocytic granulocytic metaplasia (C MGM) belong to the Philadelphia chromosome-negative (Ph-) myeloprolife rative disorders. The megakaryocytes in Ph+-ET and Ph+-CGL are abnorma l and small with round nuclei, showing little lobulation. Both the num ber and size of megakaryocytes in Ph-ET, -PV and -CMGM are typically i ncreased. Enlarged megakaryocytes with mature cytoplasm and multilobul ated nuclei and their tendency to cluster in a normal or slightly incr eased cellular bone marrow represent the hallmark of ET. In reactive t hrombocytosis the size and morphology of increased megakaryocytes are normal. The characteristic increase and clustering of enlarged mature and pleomorphic megakaryocytes with multilobulated nuclei and prolifer ation of erythropoiesis in a moderate to marked hypercellular bone mar row with hyperplasia of dilated sinuses is the diagnostic hallmark of untreated PV. In secondary polycythaemia, in which increased cellulari ty of the erythroid cell line may be present, the number, size and mor phology of megakaryocytes remain small and normal. CMGM, including ear ly stages without myelofibrosis and advanced myelofibrotic stages of a gnogenic myeloid metaplasia, appears to be a distinct neoplastic proli feration of neutrophilic granulopoiesis and megakaryopoiesis. The hist opathology of the bone marrow in CMGM is dominated by atypical, enlarg ed and immature megakaryocytes with cloud-like nuclei:which are not se en in ET and PV. Myelofibrosis in ET, PV and CMGM is graded in no reti culin fibrosis (MF0), early reticulin fibrosis (MF1), advanced reticul in sclerosis with minor collagen fibrosis (MF2) and advanced collagen fibrosis with or without osteosclerosis (MF3). Myelofibrosis is not a feature of ET, may occur in PV, and constitutes a prominent feature of CMGM during the natural history of the disease. (C) 1997 Elsevier Sci ence B.V.