Megakaryopoiesis in chronic myeloproliferative diseases. A morphometric evaluation with special emphasis on primary thrombocythemia.

Morphometry was employed on different entities of chronic myeloproliferative diseases (CMPD) and reactive lesions in addition to normal control specimens. The entities studied included: (1) inflammatory reactions of the bone marrow (so-called myelitis in chronic rheumatoid arthritis), (2) chronic granulocytic leukemia (CGL), (3) agnogenic myeloid metaplasia in an early hypercellular stage (so-called chronic megakaryocytic-granulocytic myelosis, CMGM), (4) agnogenic myeloid metaplasia in an advanced fibrosclerotic stage or osteomyelofibrosis/sclerosis (MF/OMS), (5) polycythemia vera (P. vera), (6) reactive thrombocytosis (TH, as a sequel of miscellaneous conditions) and (7) primary (idiopathic, essential) thrombocythemia (PTH). Evaluation was done on plastic-embedded semithin sections with a constant thickness of 3 micron in approximately 20 cases of each group of CMPD. The following parameters were determined: (1) density distributions of the megakaryocyte and non-megakaryocyte compartments, (2) arrangement of megakaryopoiesis in the bone marrow space (i.e., inhomogeneity or clustering) and (3) the fine structure of megakaryocytes in PTH, with a quantitative analysis of the nuclear morphology by circular deviation and contour factors. The megakaryocyte morphology was closely related to a facultative or obligatory increase of the platelet count in these various entities of CMPD and was separable into two major categories: (1) controls, CGL and myelitis versus (2) CMGM, MF/OMS, P. vera, TH and PTH. These two categories were distinguishable by the prominence of megakaryopoiesis in the bone marrow as well as the elevated platelet counts in the periphery. Moreover, in comparison with CMGM and MF/OMS, PTH was characterized by an apparently normal maturation and a conspicuous polyploidization of megakaryocytes according to the nuclear morphology, which was similar to that of P. vera. Our results suggest that PTH presents a monolinear growth of the megakaryopoiesis in the same way as CGL exhibits a monolinear proliferation of the neutrophilic granulopoiesis. This is in contrast to the mixed cellularity of both the megakaryocyte and granulocyte lineage in CMGM and MF/OMS.