Chapter 103. Polycythemia Vera and Other Myeloproliferative Diseases (Part 6)

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This marrow section shows the marrow cavity replaced by fibrous tissue composed of reticulin fibers and collagen. When this fibrosis is due to a primary hematologic process, it is called myelofibrosis. When the fibrosis is secondary to a tumor or a granulomatous process, it is called myelophthisis. Diagnosis While the clinical picture described above is characteristic of chronic IMF, all of the clinical features described can also be observed in PV or CML. Massive splenomegaly commonly masks erythrocytosis in PV, and reports of intraabdominal thromboses in chronic IMF most likely represent instances of unrecognized PV. ...

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Nội dung Text: Chapter 103. Polycythemia Vera and Other Myeloproliferative Diseases (Part 6)

Chapter 103. Polycythemia Vera and Other Myeloproliferative Diseases (Part 6) Figure 103-2
This marrow section shows the marrow cavity replaced by fibrous tissue composed of reticulin fibers and collagen. When this fibrosis is due to a primary hematologic process, it is called myelofibrosis. When the fibrosis is secondary to a tumor or a granulomatous process, it is called myelophthisis. Diagnosis While the clinical picture described above is characteristic of chronic IMF, all of the clinical features described can also be observed in PV or CML. Massive splenomegaly commonly masks erythrocytosis in PV, and reports of intraabdominal thromboses in chronic IMF most likely represent instances of unrecognized PV. In some patients with chronic IMF, erythrocytosis has developed during the course of the disease. Furthermore, since many other disorders have features that overlap with chronic IMF but respond to distinctly different therapies, the diagnosis of chronic IMF is one of exclusion, which requires that the disorders listed in Table 103-3 be ruled out. A diagnostic algorithm has been proposed but does not distinguish one disease causing myeloid metaplasia from another. The presence of teardrop-shaped red cells, nucleated red cells, myelocytes, and promyelocytes establishes the presence of extramedullary hematopoiesis,
while the presence of leukocytosis, thrombocytosis with large and bizarre platelets, and circulating myelocytes suggests the presence of a myeloproliferative disorder as opposed to a secondary form of myelofibrosis (Table 103-3). Marrow is usually not aspirable due to increased marrow reticulin, but marrow biopsy will reveal a hypercellular marrow with trilineage hyperplasia and, in particular, increased numbers of megakaryocytes in clusters and with large, dysplastic nuclei However, there are no characteristic morphologic abnormalities that distinguish IMF from the other chronic myeloproliferative disorders. Splenomegaly due to extramedullary hematopoiesis may be sufficiently massive to cause portal hypertension and variceal formation. In some patients, exuberant extramedullary hematopoiesis can dominate the clinical picture. An intriguing feature of chronic IMF is the occurrence of autoimmune abnormalities such as immune complexes, antinuclear antibodies, rheumatoid factor, or a positive Coombs' test. Whether these represent a host reaction to the disorder or are involved in its pathogenesis is unknown. Cytogenetic analysis of blood is useful both to exclude CML and for prognostic purposes, because complex karyotype abnormalities portend a poor prognosis in chronic IMF. For unknown reasons, the number of circulating CD34+ cells is markedly increased in chronic IMF (>15,000/µL) compared to the other chronic myeloproliferative disorders, unless they too develop myeloid metaplasia.
Importantly, approximately 45% of chronic IMF patients, like patients with its companion myeloproliferative disorders PV and ET, express the JAK2 V617F mutation, often as homozygotes. Such patients had a poorer survival in one retrospective study but not in another, where they were found to be older and to have higher hematocrits than those patients who were JAK2 V617F-negative. Complications Survival in chronic IMF varies according to specific clinical features (Table 103-4) but is shorter than in patients with PV or ET. The natural history of chronic IMF is one of increasing marrow failure with transfusion-dependent anemia and increasing organomegaly due to extramedullary hematopoiesis. As with CML, chronic IMF can evolve from a chronic phase to an accelerated phase with constitutional symptoms and increasing marrow failure. About 10% of patients develop an aggressive form of acute leukemia for which therapy is usually ineffective. Important prognostic factors for disease acceleration include anemia, leukocytosis, thrombocytopenia, the presence of circulating myeloblasts, older
age, the presence of complex cytogenetic abnormalities, and constitutional symptoms such as unexplained fever, night sweats, or weight loss.