[Morphology of megakaryocytes in hematologic diseases]

Ultrastructural Alterations of Megakaryocytes in Some Hematologic Disorders

Bone marrow and peripheral blood samples of patients affected by hematologic disorders involving the megakaryocytic line were examined at the electron microscope. While in idiopathic thrombocytopenic purpura the megakaryocytes appeared almost normal, in primary thrombocythemia there were various ultrastructural alterations interpreted as a counterpart of ineffective thrombocytopoiesis. In one patient with blastic chronic myeloid leukemia and in another with acute megakaryoblastic leukemia, the electron microscope study was very useful in the identification of immature megakaryocytes. In fact, analysis of various ultrastructural parameters allowed some blast cells to be attributed to the megakaryocytic series. Furthermore, platelet demarcation system abnormalities and alterations of the circulating thrombocytes confirm the hypothesis that there is a block in megakaryocytic maturation.

Atypical micromegakaryocytes, promegakaryoblasts and megakaryoblasts: a critical evaluation by immunohistochemistry, cytochemistry and morphometry of bone marrow trephines in chronic myeloid leukemia and myelodysplastic syndromes

A morphometric analysis of bone marrow trephine biopsies has been performed to study the frequency and planimetric characteristics of so-called atypical micromegakaryocytes in chronic myeloid leukemia (CML) and myelodysplastic syndromes (MDS). In addition, an attempt was made to discriminate this particular cell population from small immature elements of megakaryocytopoiesis, such as promegakaryoblasts and megakaryoblasts. The staining reactions employed included periodic acid-Schiff (PAS), alpha-naphthyl acetate esterase (ANAE) and immunohistochemistry with a monoclonal antibody against platelet glycoprotein IIIa (Y2/51-CD61). Comparison of the various staining reactions applied to the different megakaryocytic elements together with morphometric measurements resulted in a clearcut identification of promegakaryoblasts. These were defined as the earliest immature and exclusively CD61-positive precursors. Atypical micromegakaryocytes were characterized by their dysplastic features and strong ANAE reactivity in addition to their positive CD61 staining. When stringent diagnostic criteria (diameter ranging between 10 to 15 microns, mean size about 12 microns) were applied, this abnormal cell population comprised less than 10% of total megakaryocytopoiesis in CML and MDS. It may be assumed that dysmegakaryocytic features in the latter disorders are partially generated by small to medium-sized megakaryocytes (diameter less than 30 microns). In conclusion, the relative frequency of promegakaryoblasts in the normal bone marrow (range 6-8%) is confirmed by evaluation of the immunohistochemical and cytochemical staining methods (CD61 and ANAE). Furthermore, the ANAE reaction facilitates the recognition of atypical micromegakaryocytes as well as small megakaryocytes. Thus cytochemistry provides a better insight into alterations of these cell lineages in various pathological conditions.

An immunomorphometric study on megakaryocyte precursor cells in bone marrow tissue from patients with chronic myeloid leukemia (CML)

An immunomorphometric study was performed on trephine biopsies of the bone marrow in 41 patients with chronic myeloid leukemia (CML) to determine number and size of megakaryocytic precursor cells (pro- and megakaryoblasts). For specific staining, a monoclonal antibody against platelet glycoprotein IIIa (Y2/51) was employed which is applicable on routinely fixed and paraffin embedded tissue. In comparison with control specimens from 15 patients, in CML morphometric analysis revealed an increase in the total amount of megakaryocytes per square and cubic millimeter marrow tissue, but particularly in patients with thrombocythemia. Moreover, a non-disorderly expansion of the megakaryocyte precursor pool was recognizable by showing a relative frequency of pro- and megakaryoblasts in congruence with the normal value. In this context a significant correlation between the counts for Y2/51-positive megakaryocytic elements and promegakaryoblasts with the corresponding platelet values was encountered. The more mature stages of megakaryopoiesis (pro- end megakaryocytes) disclosed a relevant shift to smaller cell forms with rounded cell perimeters and a more compact aspect of their nuclei. Additionally, in 6 patients with CML, evolution into a subacute and manifest (micro)-megakaryoblastic transformation accompanied by myelofibrosis could be demonstrated by a retrospective review of file material.

Histomorphometry of bone marrow biopsies in chronic myeloproliferative disorders with associated thrombocytosis--features of significance for the diagnosis of primary (essential) thrombocythaemia

A histomorphometric analysis was performed on trephine biopsies of the bone marrow in 55 patients with chronic myeloproliferative disorders (CMPDs) and marked thrombocytosis (platelet count exceeding 600 x 10(9)/l). This study aimed at discriminating primary (essential) thrombocythaemia (PTH) from the various other subtypes of CMPDs presenting with thrombocytosis. Following the diagnostic requirements postulated by the Polycythemia-vera-Study-Group for PTH and polycythaemia vera rubra (P.vera) and the generally accepted criteria for the establishment of chronic myeloid leukaemia (CML) and agnogenic myeloid metaplasia (AMM), our cohort of 55 patients was divided into the following subgroups: CML (16 cases), P.vera (11 cases), AMM (13 cases) and finally PTH (15 cases). Histomorphometric measurements revealed that PTH was distinguishable from the other subtypes of CMPDs with respect to several histological variables: patients with PTH had a normal amount of neutrophilic granulo- and erythrocytopoiesis as well as a non-increased content of reticulin (argyrophilic) fibers in contrast to the findings in CML, P.vera and of course AMM. Moreover, sizes of megakaryocytes and their nuclei were significantly greater in PTH and internalization of haematopoietic cells (emperipolesis) was more frequently encountered in comparison with the other subtypes of CMPDs. Deviation of the circular perimeter of megakaryocyte shape was most prominently expressed in CML and AMM, and consequently generated an increased number of a-nuclear cytoplasmic fragments. In contrast to this feature aberration of the nuclei from a circular outline occurred in a less pronounced way in CML, but was excessive in P.vera, AMM and PTH. Our morphometric evaluation demonstrates that certain histological features may serve as a valuable aid in discriminating PTH from the other occasionally thrombocythaemic subtypes of CMPDs.

Chronic myeloproliferative disorders (CMPD)

The wide clinical range of CMPD can be understood as leukaemia of pluripotent stem cells according to the pathogenic concepts reviewed above. Blastic metamorphoses of CMPD are regressions to a more primitive level of cellular differentiation. The predominant proliferative cell line characterizes the classical entities of PV, PT and CML, and their different prognoses. Pure erythrocytic and megakaryocytic proliferations are more compatible with sustained physiologic bone marrow functions than granulocytic proliferations. The combinations of granulocytic and megakaryocytic growth are especially prone to develop MF/OMS, in which participation of immune reactions, of granulocytic and of platelet factors is probable. An etiologic role for ineffective thrombocytopoiesis is supported by experimental as well as by histologic evidence. Myelofibrosis and osteomyelosclerosis may have similar causes, but develop independently. The prevalence of the female sex among thrombocythaemic patients was proven statistically also for the increase of giant type megakaryocytes in the form of clusters in the bone marrow, and for longer median survival of females in CMPD, especially when there is megakaryocytosis in the bone marrow. It is assumed that females may be better protected against the detrimentous effects of abnormal platelet production. An arbitrary classification according to haematologic and histologic criteria was applied to PV, PT and CML, and groups with typical and atypical haematologic and histologic signs were distinguished. The latter cannot be separated from each other by their various haematologic manifestations, but by histology and their different propensity to progress into more immature and/or fibrotic stages. Three major groups are characterized by histology: mixed granulocytic-megakaryocytic myelosis with giant megakaryocytic clusters, a similar variant with diffuse distribution of giant megakaryocytes, and immature and/or pleomorphic megakaryocytic myelosis. Transitions from each of these groups have been observed as well as transitions from each of the typical CMPD-entities into these less typical forms. CML, frequently accompanied by dwarf-megakaryocytes, often develops into pleomorphic megakaryocytic or blastic myelosis. Blastic dedifferentiation and myelofibrosis manifest themselves as closely related end stages, to which principally all groups proceed after a longer or shorter period of time, modified by the proliferating cell lines in each group. Clinical, experimental and histologic evidence of this natural history has been reviewed, with special emphasis on the re-evaluation of technically optimal bone marrow biopsies of untreated patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of circulating micromegakaryocytes in a case of erythroleukemia

A 26-year-old man with erythroleukemia was found to have circulating micromegakaryocytes . Megakaryocytic features were defined by morphologic and cytochemical studies using light and electron microscopy with platelet-megakaryocyte peroxidase staining. This appears to be the first reported instance of erythroleukemia with circulating micromegakaryocytes .

Density distribution and size of megakaryocytes in inflammatory reactions of the bone marrow (myelitis) and chronic myeloproliferative diseases

Morphometric evaluation was performed on semi-thin sections of core biopsies of the bone marrow and included 20 cases of each group of diseases besides control specimens. (i) Hyperergic myelitis of rheumatic origin. (ii) Chronic granulocytic leukaemia (CGL). (iii) Polycythaemia vera (P. vera). (iv) Chronic megakaryocytic-granulocytic myelosis (CMGM). (v) Myelofibrosis or osteomyelosclerosis (MF/OMS). The following classification of megakaryopoiesis was applied: normal megakaryocytes; giant forms; microforms; intussusceptions; cytoplasmic fragments; naked nuclei. The density distribution shows an increase of megakaryocyte number in those 5 different marrow disorders, ranging from about 13/mm2 in the normal sample up to 65 cells/mm2 in MF/OMS. Microforms are most frequently encountered in CGL, whereas giant megakaryocytes, intussusceptions and many cytoplasmic fragments characterize P. vera, CMGM and MF/OMS. Our measurements suggests 3 distinct categories of bone marrow lesions with corresponding alterations of the megakaryopoiesis: (i) myelitis and CGL; (ii) P. vera; (iii) CMGM and MF/OMS.

Megakaryocytes in cubital venous blood in patients with chronic myeloproliferative diseases

33 patients with chronic myelo-proliferative disease were investigated for megakaryocytes in cubital venous blood. 6 Patients had chronic myeloid leukaemia, 11 polycythaemia vera and 16 myelofibrosis. In all patients, a significantly higher number of megakaryocytes than in normal adult humans was found. In patients with chronic myeloid leukaemia and myelofibrosis, an increased number of intact megakaryocytes was found, indicating thrombopoiesis in the peripheral part of the upper extremity. 2 patients with myelofibrosis showed a % of intact megakaryocytes greater than 25, as found in blood from the inferior vena cava in normal adults. In patients with chronic myeloid leukaemia, some of the megakaryocytes were smaller than normal, whereas in myelofibrosis, some of the megakaryocytes were larger than normal, with increased lobulation of nuclei. Active thrombopoiesis in the peripheral part of the extremities can be of great importance, when splenectomy is considered in treatment of myelofibrosis.

Abnormalities of megakaryocytes in myelitis and chronic myeloproliferative diseases

A planimetric study of megakaryopoiesis in various chronic myeloproliferative diseases (CMPD) was performed and the results compared with those from controls and myelitis of rheumatic origin. Morphometric measurements included at least 200 megakaryocytes in each case observed in Giemsa-stained semithin sections of resin-embedded core biopsies. Twenty specimens were evaluated from the controls and inflammatory disorders and from each of the following CMPD: 1, chronic granulocytic leukaemia (CGL); 2, polycythaemia vera (P. vera); 3, chronic megakaryocytic-granulocytic myelosis without or with minimal increase in reticulin fibre content (CMGM); 4, myelofibrosis or osteomyelosclerosis (MF/OMS). Megakaryocytes were classified as follows: 1, normal megakaryocytes at all stages of maturation; 2, giant forms; 3, microforms; 4, intussusceptions; 5, a-nuclear cytoplasmic fragments; 6, naked nuclei or necrotic forms. The results of this study demonstrate obvious abnormalities of megakaryopoiesis in addition to the increase in absolute numbers of megakaryocytes per marrow area and their different sizes as reported earlier (Thiele et al. 1982). Aberrations are particularly conspicuous when pure granulocytic proliferation or neoplasia of CGL is compared with the so-called mixed cellularity of megakaryocytes and granulocytes in CMGM including MF/OMS. Abnormalities of the giant forms of megakaryocytes are especially evident and comprise irregular cellular and nuclear perimeters (as calculated by a modified shape factor) in the two latter entities (CMGM-MF/OMS). This remarkable feature is associated with a disorganization of nuclear development and/or a disproportionate nuclear-cytoplasmic ratio which has never been observed in CGL previously. In combination with this striking cellular anomaly, which is compatible with an extreme amoeboid shape of giant forms in CMGM and MF, intussuceptions and a-nuclear cytoplasmic fragments are frequently encountered. The final stage of megakaryopoiesis, i.e. naked nuclei, are increased in number in all CMPD, probably because of enhanced proliferation and platelet shedding. Naked nuclei are often small in CGL (as remnants of the frequent micromegakaryocytes) and large in P. vera and CMGM/MF (depending on the high incidence of giant megakaryocytes in these latter disorders).

Polycythemia vera: electron microscopy of the bone marrow in 10 non-treated patients. A thin section and freeze-fracture study

Electron microscopy (thin sections and freeze-fracture replicas) was performed on the bone marrow of ten patients with Polycythemia vera prior to any treatment. In addition to a hyperplasia of all three cell lineages and the sinuses, atypias were observed in the maturing erythroblasts. These aberrations of normal development consisted mainly of deep invaginations of the nuclear envelope in proerythroblasts and conspicuous nuclear clefts in erythro- and normoblasts. In comparison with similar changes in dyserythropoietic and aplastic anemia as well as leukemia these alterations are discussed in connection with disturbances of DNA synthesis. Further atypias involved megakaryopoiesis which displayed microforms probably as an evidence for maturation arrest. These ultrastructural abnormalities and their morphological features of a neoplastic proliferation of all three cell lineages in Polycythemia vera are in good agreement with the new concept of a transformation of a pluripotent stem cell with clonal character.

The blast crisis of chronic granulocytic leukaemia: megakaryoblastic nature of cells as revealed by the presence of platelet-peroxidase--a cytochemical ultrastructural study

The origin of cells in the blast crisis of some cases of chronic granulocytic leukaemia (CGL) remains controversial. Difficulties arise from the lack of cytochemical characteristics of differentiation. This report concerns the nature of cells in the blast crisis of a case of CGL in which blast cells exhibited an undifferentiated or lymphoid appearance by light and electron microscopy. The majority (90%) of such cells contained a peroxidase in the endoplasmic reticulum distinct from myeloperoxidase. In addition, some micromegakaryocytes could be recognized among the peroxidase reactive cells, by the presence of typical granules and demarcation membranes. Since this peroxidase exhibited identical characteristics to that of normal megakaryocytic precursors, these blast cells could be identified as megakaryoblasts. These data emphasize the possible megakaryoblastic nature of cells occurring in other cases of CGL blast crisis.

Chronic megakaryocytic-granulocytic myelosis--an electron microscopic study. I. Megakaryocytes and thrombocytes

The fine structure of the bone marrow in chronic megakaryocytic-granulocytic myelosis (CMGM) was studied in 5 nontreated patients to investigate possible malignant proliferation of megakaryocytes and the role of megakaryopoiesis in fibrillogenesis, terminating in osteomyelofibrosis. In comparison with normal megakaryopoiesis there is an enormous increase of the megakaryocytic cell line and many immature and atypical forms are seen. Most conspicuous are microforms, nuclear-cytoplasmic disorganization and nuclear inclusions. Asynchrony of maturation causes abnormal thrombocytogenesis with premature detachment of platelets resulting in immature and peculiar giant forms of thrombocytes. Besides megakaryocytes appearing superficially normal the maturation anarchy of many cells is so severe that by analogy with observations in other leukaemic cells these abnormalities are thought to be representative of a malignant growth. Moreover, there is a striking accumulation of microfibrils and single collagen fibres around megakaryoblasts. Since these cells contain all those organelles commonly associated with fibre production the initial step for fibrillogenesis may therefore arise from the megakaryoblasts prior to platelet release, or any fibroblast proliferation.