Megakaryocytes in chronic myeloproliferative disorders: numerical density correlated between different entities

Clinical and pathological criteria for the diagnosis of essential thrombocythemia, polycythemia vera, and idiopathic myelofibrosis (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.

Polycythemia rubra vera versus secondary polycythemias. A clinicopathological evaluation of distinctive features in 199 patients

To determine parameters of distinctive value in polycythemia rubra vera (PV) versus secondary polycythemias (SP), a clinicopathological study was performed on 199 patients. These presented with a borderline to marked elevation of the hemoglobin level (> 18 g/dl in men and > 16 g/dl in women). Evaluations of clinical features and bone marrow histopathology were carried out independently. According to the results derived from laboratory data and representative pretreatment trephine biopsies, three groups of patients emerged: group I presenting with the concordant clinical and morphological findings of early to manifest PV (136 patients), group II consisting of 55 patients with the congruent signs and symptoms of SP mostly caused by various chronic bronchopulmonal disorders, and finally eight patients (group III) with divergent findings. Between group I and II patients (PV versus SP), a number of clinical parameters proved to be significantly different. With the exception, of the red cell mass, platelet count, leukocyte alkaline phosphatase, LDH, spleen size, and the erythropoietin level had a significantly discriminating impact. Morphological features of distinctive value consisted of a set of specific lesions. Contrasting SP with an only borderline to slight increase in cellularity associated with a moderate enlargement of the erythroblastic islets, PV was always characterized by a significant increase in hematopoiesis, revealing a trilinear proliferation (panmyelosis). Megakaryopoiesis was strikingly different in PV as compared to SP by displaying clustering and a pleomorphous appearance. i.e., very small and giant megakaryocytes with staghorn-like nuclei were neighboring each other. Moreover, conspicuous alterations of the interstitial compartment were recognizable in SP. These consisted of deposits of cell debris in histiocytic reticular cells, iron-laden macrophages, and a plasmacytosis, implying an inflammatory reaction. These changes were only very rarely observed in PV, as opposed to a minimal to slight increase in reticulin fibers in about 12% of patients. In conclusion, a more elaborate evaluation of bone marrow features resulted in a set of diagnostic criteria with discriminating capacity that should be considered in prospective clinical trials.

Molecular detection of c-mpl thrombopoietin receptor gene expression in chronic myeloproliferative disorders

BACKGROUND

Chronic myeloproliferative disorders (CMPD) originate from a pluripotent haematopoietic progenitor cell but show a marked degree of heterogeneity, especially between Philadelphia chromosome positive and negative disease entities. Abnormal megakaryopoiesis is a frequent finding in CMPD, often associated with thrombocythaemic cell counts. Recent experimental data have suggested that the c-Mpl thrombopoietin receptor, together with its ligand thrombopoietin, are not only the major physiological regulators of megakaryopoiesis and platelet production, but also play a crucial role in chronic myeloproliferation.

METHODS

A total of 18 peripheral blood mononuclear cell samples obtained from patients with CMPD (chronic myelocytic leukaemia (CML), n = 10; polycythaemia vera (PV), n = 6; and primary thrombocythaemia (PTH), n = 2) were analysed for c-mpl mRNA using the reverse transcriptase polymerase chain reaction (RTPCR). In another 20 patients (CML, n = 10; chronic megakaryocytic granulocytic myelosis (CMGM), n = 3; PV, n = 3; PTH, n = 4), we compared the number of haematopoietic progenitors expressing c-Mpl, as characterised by coexpression with the CD34 antigen, in the bone marrow using double immunofluorescence staining.

RESULTS

c-mpl mRNA was detected in all samples from patients with CML analysed, whereas only two of six PV and one of two PTH samples were positive (p < or = 0.008; chi 2 test). Expression of the c-mpl receptor gene was absent in healthy subjects used as controls. Similarly, an increase of c-Mpl expressing CD34 positive haematopoietic cells was detected in seven of 10 bone marrow aspirates obtained from patients with CML. Increased numbers of c-Mpl positive CD34 positive cells were found in only one of four patients with PTH, whereas in PV and CMGM the numbers of c-Mpl positive CD34 positive cells did not exceed normal values, despite thrombocythaemic cell counts.

CONCLUSIONS

These data confirm recent findings showing an impaired expression of the c-mpl thrombopoietin receptor gene in Philadelphia chromosome negative CMPD when compared with patients with Philadelphia chromosome positive CML. The relevance of this observation to the functional and morphological characteristics of abnormal megakaryopoiesis remains unclear. Thrombocythaemic cell counts and a mature phenotype in megakaryocytes occur frequently in Philadelphia chromosome negative CMPD but require an intact c-Mpl receptor under physiological conditions. Therefore, further studies are warranted to elucidate the mechanisms contributing to megakaryopoiesis in CMPD disease entities with decreased c-mpl gene expression.

Clinicopathological diagnosis and differential criteria of thrombocythemias in various myeloproliferative disorders by histopathology, histochemistry and immunostaining from bone marrow biopsies

Differentiation of essential thrombocythemia (ET) from thrombocythemias occurring in various subtypes of chronic myeloproliferative disorders (MPDs) is controversial, because of the lack of uniform clinical and morphological criteria. A retrospective clinicopathologic study was performed on 375 patients presenting with a MPD and a platelet count exceeding 500 x 10(9/)l. For comparison 35 patients with reactive thrombocytosis (RT) and five patients with a myelodysplastic syndrome (MDS-5q(-) syndrome) were enrolled into this study. In addition to a complete clinicopathological work-up, procedures included histochemical and immunological staining techniques and morphometry of bone marrow biopsies for proper evaluation of megakaryocytes (CD61) and erythroid precursors (Ret40f). Because of the high patient's age on admission, relative survival rates with corresponding disease-specific loss of life expectancy were calculated. Analysis of clinical and morphological characteristics, in particular megakaryopoiesis revealed features which enabled a clear-cut distinction between thrombocythemias in MPDs and thrombocythemic states in MDS. This rationale proved to be most important for the diagnostic discrimination of the 33 patients with initial (prefibrotic) stages of idiopathic myelofibrosis (IMF) from ET (40 patients). A new set of relevant criteria for the diagnosis of IMF with special regard to early stages and its distinction from ET has been proposed. Hemorrhagic episodes were more frequently observed in ET than in thrombocythemias associated with polycythemia vera (PV). Computation of specific loss of life expectancy revealed two extremes: thrombocythemia in CML (81%) and ET (3%), whereas thrombocythemias in PV and IMF did not show a significantly different life loss (19-22%). The revised criteria for ET, PV and IMF are reliable by taking histopathological features from bone marrow biopsies into consideration, particularly for the diagnosis of ET and its differentiation from thrombocythemias as a presenting symptom accompanying the various subtypes of MPDs.

The histopathology of chronic myeloproliferative diseases

This chapter discusses the histopathology of five groups of chronic myeloproliferative diseases: chronic myeloid leukaemia, polycythaemia vera, essential thrombocythaemia, chronic idiopathic myelofibrosis and unclassifiable myeloproliferation. Histological staging of the four haematologically defined diseases is performed by grading the three most prominent variables: megakaryocytes, fibres and blasts. Histological outcome is correlated to the staging of diagnostic bone marrow biopsies; megakaryocytic involvement is correlated with the risk of myelofibrosis. An excess of blasts is related to the risk of leukaemic transformation. The progression of myelofibrosis depends on the grade of fibre increase at diagnosis. These three statements are highly significant and valid for all types of chronic myeloproliferative disorders. The results of cytogenetics are discussed in relation to the histological classification for these patient groups. Changes in bone marrow histology following myelosuppressive therapy is presented. Prospective studies under standardized protocol therapy are recommended, so that the long-term effects of therapy can be assessed.

Clinicopathological impact of the interaction between megakaryocytes and myeloid stroma in chronic myeloproliferative disorders: a concise update

In this report an attempt has been made to discuss some of the issues pertinent to myelofibrosis complicating chronic myeloproliferative disorders (CMPDs) that are significantly associated with megakaryocyte function. In this context, biochemical, clinical and particularly morphological features were reviewed. Morphological findings based on elaborate techniques were in keeping with the assumption that in chronic myeloid leukemia (1) the number of CD61-positive megakaryocytes, and in particular their precursors were the parameters most closely associated with myelofibrosis (2) an increased content of reticulin fibers in follow-up biopsies significantly correlated with laboratory data indicative of a high tumor burden (anemia, peripheral blasts, hepatosplenomegaly) and thus a more advanced stage of the disease process (3) even a slight increase in reticulin, i.e. doubling of the normal fiber density was associated with a worse prognosis independent of therapeutic regimens given (4) Dynamics of myelofibrosis was significantly influenced by treatment. In this context, calculation of the myelofibrosis progression index (MPI) revealed a higher score following interferon therapy compared with busulfan. In addition, in idiopathic myelofibrosis (5) the evolution of myelofibrosis was unpredictable and according to the MPI, progression occurred at a relatively low rate (6) proliferation and dilatation of sinusoids accompanying intravascular hematopoiesis and collagen type IV deposits were predominant features in later (fibro-osteosclerotic) stages in the course of disease (7) transmural migration of megakaryocytes demonstrated by three dimensional reconstruction revealed a mole-like tunneling through the thickened sinusoidal wall. A very careful assessment of the numerous correlations between bone marrow features and laboratory data will allow clinicians and pathologists to gain a better insight into the mutual relationships between hematological and morphological findings in CMPDs.

A megakaryocyte analysis of the bone marrow in patients with myelodysplastic syndrome, myeloproliferative disorder and allied disorders

A morphometric analysis was performed on aspirate clots of bone marrow to identify the presence of atypical megakaryocytes after immunohistological staining with a monoclonal antibody against Factor VIII. This study included cases of myelodysplastic syndrome (MDS), myeloproliferative disorder (MPD), aplastic anaemia (AA), idiopathic thrombocytopenic purpura (ITP), chronic myelogenous leukaemia (CML), and control cases free from any haematological disease. Quantitative and qualitative abnormalities of megakaryocytes were assessed using an image analyser and a personal computer to perform a morphometric analysis of the number (per mm2), arrangement (microns), nuclear size (microns2), cell size (microns2), nuclear size/cell size (N/C) ratio, and nuclear contour index (NCI). Micromononuclear megakaryocytes were detected in MDS, while in MPD, large over-mature magakaryocytes were observed to increase in number. In AA, the megakaryocytes decreased dramatically in number without showing any morphological abnormality. In CML, the megakaryocytes also increased without any remarkable morphological abnormality. In ITP, only the NCI increased. The above results show that MDS is characterized by the presence of atypical micromegakaryocytes, while MPD is characterized by atypical large over-mature megakaryocytes.

Evidence from molecular genetic and cytogenetic analyses that bone marrow histopathology is reliable in the diagnosis of chronic myeloproliferative disorders

The reliability of histopathological diagnosis in bone marrow specimens from patients with chronic myeloproliferative disorders (CMPD) was evaluated by correlating the histological findings with molecular genetic and cytogenetic analyses of the Ph1-translocation. A rearrangement of m-bcr was detected only in patients (28/30) diagnosed histologically as chronic myeloid leukemia (CML). This finding was supported by the presence of a Ph1-chromosome in 24/26 patients with CML examined. All the patients with other types of CMPD, including polycythemia vera (PV), primary thrombocythemia (PTH) and chronic megakaryocytic-granulocytic myelosis (CMGM), as well as those with unclassifiable CMPD (CMPD.UC) were Ph1-negative (n = 38). The histopathological discrimination of CML from Ph1-negative varieties of CMPD was also reliable for patients with myelofibrosis complicating CML, CMGM and CMPD.UC. The results demonstrate that bone marrow histopathology allows a reliable diagnosis of CML. This is in contrast with hematological data such as high platelet counts which show considerable overlapping in the various forms of CMPD.

Planimetric analysis of megakaryocytes in the four main groups of chronic myeloproliferative disorders

Planimetry of megakaryocytes (MK) was performed in bone marrow biopsies (BMBs) from patients with chronic myeloproliferative disorders (CMPD) to substantiate cytomorphologic differences in this cell lineage between the four main groups of CMPD. The biopsy specimens were classified histologically prior to morphometry, according to the Hannover Classification of CMPD. Five histological groups were investigated, evaluating between 21 and 30 biopsies in each group. The five groups were as follows: (1) Chronic myelocytic leukemia (CML) of common type (CML.CT), (2) CML with megakaryocytic increase (CML.MI), (3) polycythemia vera (P. vera), (4) primary thrombocythemia (PTH), and (5) chronic megakaryocytic-granulocytic myelosis (CMGM). The results of five variables, i.e. the cellular and nuclear size, the cellular and nuclear form factor, and nuclear segmentation, were determined in at least 50 MK per BMB. The results reveal significant differences in MK nuclear and cellular size, as well as in nuclear segmentation between CML and the three other groups in that the nuclear and cellular size of the MK in CML are smaller than in P. vera, PTH, and CMGM. Moreover, the degree of nuclear segmentation or lobulation differs significantly between the three disorders characterized by large MK. Discriminant analysis permits 78-100% reliability of reclassification by morphometry compared with the histologic classification. A reduced reliability of the morphometric classification to around 80% was found between P. vera and PTH, as well as between P. vera and CMGM. In the design of this study, morphometry of MK lends added weight to the subjective classification of these disorders.

The impact of megakaryocyte proliferation of the evolution of myelofibrosis. Histological follow-up study in 186 patients with chronic myeloid leukaemia

A histological study on sequential bone marrow biopsies in patients with chronic myeloid leukaemia (CML) was performed. We wished to answer the question as to whether a different content of megakaryopoiesis in the bone marrow of CML patients has a prognostic significance for the development of myelofibrosis during the course of disease. In addition, the significance of possible changes in the quantity of megakaryopoiesis in this process was assessed. In 186 patients who had no fibre increase at first diagnosis, the rate of subsequent myelofibrosis varied from 19% for the common or granulocytic subtype (CML.CT) to 40% for patients with features of megakaryocytic increase (CML.MI). No significant differences were found either in the rapidity of progression to fibrosis or in the final rate of osteomyelosclerosis. Whereas in CML.MI most patients (75%) showed an increase of fibres only, this was accompanied by an additional increase of megakaryocytes in CML.CT, changing the histological pattern from CML.CT to .MI or .MP, respectively. The data therefore revealed a correlation between fibre increase and subtyping of CML as suggested by the Hannover classification of chronic myeloproliferative diseases. Subtypes of CML with megakaryocytic increase could be shown to present a "pre-myelofibrotic" stage of disease and may therefore be conceived as a particular pathway of acceleration.

Histologic findings in bone marrow biopsies of patients with thrombocythemic cell counts

Histologic diagnoses from bone marrow biopsies were analyzed in a total of 1165 patients presenting with thrombocythemic platelet counts at initial examination. Two cut-off points suggested by the Polycythemia Vera Study Group to define thrombocythemia by platelet counts were compared: the former limiting value of 1000 x 10(9)/l platelets versus the recently proposed value of 600 x 10(9)/l. The percentage of all nonproliferative disorders was 41% under the lower, dropping to 11% under the high cut-off point. The respective figures for myeloproliferative disorders increased from 49% under the lower to 74% under the high limiting value. Primary thrombocythemia was included in 72% by the lower, and in only 40% by the high limiting value when classified by its histologic pattern in bone marrow biopsy. A striking decrease of platelet counts occurs, related to fiber increase, among each of three main groups of myeloproliferative disorders: in CML with megakaryocytic predominance from 40% down to 25%, in megakaryocytic-granulocytic myelosis (primary, i.e., agnogenic myelofibrosis) from 36.6% to 10%, and in primary thrombocythemia from 72.6% to 28.6% in cases with reticulin sclerosis.

Cytogenetics of chronic myelogenous leukemia (CML) correlated to the histopathology of bone marrow biopsies

Cytogenetic findings were correlated to histopathological bone marrow findings evaluated simultaneously in 103 patients with chronic myelogenous leukemia (CML). CML was subtyped histologically according to the number of megakaryocytes and increase of fibers or blasts within the bone marrow. The Philadelphia chromosome (Ph 1) was found in 88.3% of all patients (91/103). Chromosome aberrations additional to the Ph 1-chromosome were noticed in 20 of 91 (22%) cases. The additional karyotype changes occurred significantly more frequently among patients with increase of fibers in the bone marrow compared with patients without increase of fibers or blasts (p less than 0.05). Karyotype changes associated with increase of fibers in Ph 1-positive cases of CML were trisomy 8 and 19, +Ph1, t (1; 11), and i (17q). Ph 1-positive CML patients with additional karyotype changes had a significantly shorter survival (p less than 0.04) than Ph 1-positive patients without additional chromosome aberrations. Our results suggest that histopathological examination of the bone marrow should be considered in the evaluation of cytogenetic markers in chronic myeloproliferative disorders.