Chapter 103. Polycythemia Vera and Other Myeloproliferative Diseases (Part 8)

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Chronic Idiopathic Myelofibrosis: Treatment No specific therapy exists for chronic IMF. Anemia may be due to gastrointestinal blood loss and exacerbated by folic acid deficiency, and in rare instances, pyridoxine therapy has been effective. However, anemia is more often due to ineffective erythropoiesis uncompensated by extramedullary hematopoiesis in the spleen and liver. Neither recombinant erythropoietin nor androgens, such as Danazol, have proved consistently effective as therapy for anemia. Erythropoietin may worsen splenomegaly and will be ineffective if the serum erythropoietin level is 125 mU/L. A red cell splenic sequestration study can establish the presence of hypersplenism, for which splenectomy is...

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Chapter 103. Polycythemia Vera and Other Myeloproliferative Diseases (Part 8) Chronic Idiopathic Myelofibrosis: Treatment No specific therapy exists for chronic IMF. Anemia may be due to gastrointestinal blood loss and exacerbated by folic acid deficiency, and in rare instances, pyridoxine therapy has been effective. However, anemia is more often due to ineffective erythropoiesis uncompensated by extramedullary hematopoiesis in the spleen and liver. Neither recombinant erythropoietin nor androgens, such as Danazol, have proved consistently effective as therapy for anemia. Erythropoietin may worsen splenomegaly and will be ineffective if the serum erythropoietin level is >125 mU/L. A red cell splenic sequestration study can establish the presence of hypersplenism, for which splenectomy is indicated. Splenectomy may also be necessary if splenomegaly impairs alimentation and should be performed before cachexia sets in. In this situation, splenectomy should not be avoided because of concern over rebound thrombocytosis, loss of hematopoietic capacity, or
compensatory hepatomegaly. However, for unexplained reasons, splenectomy increases the risk of blastic transformation. Splenic irradiation is, at best, temporarily palliative and associated with a significant risk of neutropenia and infection. Allopurinol can control significant hyperuricemia, and hydroxyurea has proved useful for controlling organomegaly in some patients. The role of IFN-α is still undefined and its side effects are more pronounced in the older individuals who are usually afflicted with this disorder. Glucocorticoids have been used to control constitutional symptoms and autoimmune complications and may ameliorate anemia alone or in combination with low dose thalidomide (50–100 mg/d). Allogeneic bone marrow transplantation is the only curative treatment and should be considered in younger patients; reduced-intensity conditioning regimens may permit hematopoietic cell transplantation to be extended to older individuals. Essential Thrombocytosis Essential thrombocytosis (other designations include essential thrombocythemia, idiopathic thrombocytosis, primary thrombocytosis, hemorrhagic thrombocythemia) is a clonal disorder of unknown etiology involving a multipotent hematopoietic progenitor cell manifested clinically by overproduction of platelets without a definable cause. ET is an uncommon
disorder, with an incidence of 1–2/100,000 and a distinct female predominance, in contrast to the other chronic myeloproliferative disorders. No clonal marker is available to consistently distinguish ET from the more common nonclonal, reactive forms of thrombocytosis (Table 103-5), making its diagnosis difficult. Once considered a disease of the elderly and responsible for significant morbidity due to hemorrhage or thrombosis, with the widespread use of electronic cell counters, it is now clear that ET can occur at any age in adults and often without symptoms or disturbances of hemostasis. There is an unexplained female predominance in contrast to the other chronic myeloproliferative disorders or the reactive forms of thrombocytosis where no sex difference exists. Because no specific clonal marker is available, clinical criteria have been proposed to distinguish ET from the other chronic myeloproliferative disorders, which may also present with thrombocytosis but have differing prognoses and therapy (Table 103-5). These criteria do not establish clonality; therefore, they are truly useful only in identifying disorders such as CML, PV, or myelodysplasia, which can masquerade as ET, as opposed to actually establishing the presence of ET. Furthermore, as with "idiopathic" erythrocytosis, nonclonal benign forms of thrombocytosis exist (such as hereditary overproduction of thrombopoietin) that are not widely recognized because we currently lack adequate diagnostic tools.
Table 103-5 Causes of Thrombocytosis Malignancy Infection Myeloproliferative disorders: polycythemia vera, idiopathic myelofibrosis, essential thrombocytosis, chronic myelogenous leukemia Myelodysplastic disorders: 5q-syndrome, idiopathic refractory sideroblastic anemia Postsplenectomy or hyposplenism Hemorrhage Iron deficiency anemia Surgery Rebound: Correction of vitamin B12 or folate deficiency, post-ethanol abuse
Hemolysis