Chapter 103. Polycythemia Vera and Other Myeloproliferative Diseases (Part 3)

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Diagnosis When PV presents with erythrocytosis in combination with leukocytosis, thrombocytosis, or both, the diagnosis is apparent. However, when patients present with an elevated hemoglobin or hematocrit alone, or with thrombocytosis alone, the diagnostic evaluation is more complex because of the many diagnostic possibilities (Table 103-2). Furthermore, unless the hemoglobin level is ≥20 gm% (hematocrit ≥60%), it is not possible to distinguish PV from disorders causing plasma volume contraction. Uniquely in PV, an expanded plasma volume can mask an elevated red cell mass; thus, red cell mass and plasma volume determinations are mandatory to establish the presence of an absolute...

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Chapter 103. Polycythemia Vera and Other Myeloproliferative Diseases (Part 3) Diagnosis When PV presents with erythrocytosis in combination with leukocytosis, thrombocytosis, or both, the diagnosis is apparent. However, when patients present with an elevated hemoglobin or hematocrit alone, or with thrombocytosis alone, the diagnostic evaluation is more complex because of the many diagnostic possibilities (Table 103-2). Furthermore, unless the hemoglobin level is ≥20 gm% (hematocrit ≥60%), it is not possible to distinguish PV from disorders causing plasma volume contraction. Uniquely in PV, an expanded plasma volume can mask an elevated red cell mass; thus, red cell mass and plasma volume determinations are mandatory to establish the presence of an absolute erythrocytosis and to distinguish this from relative erythrocytosis due to a reduction in plasma volume alone (also known as stress or spurious erythrocytosis or Gaisböck's syndrome). This is true even in with the discovery of the JAK2
V617F mutation, because not very patient with PV expresses this mutation, while patients without PV do. Figure 58-18 illustrates a diagnostic algorithm for the evaluation of suspected erythrocytosis. Table 103-2 Causes of Erythrocytosis Relative erythrocytosis: Hemoconcentration secondary to dehydration, androgens, or tobacco abuse Absolute erythrocytosis Hypoxia Carbon monoxide intoxication High affinity hemoglobin High altitude Pulmonary disease Right-to-left shunts Sleep-apnea syndrome
Neurologic disease Renal disease Renal artery stenosis Focal sclerosing or membranous glomerulonephritis Renal transplantation Tumors Hypernephroma Hepatoma Cerebellar hemangioblastoma Uterine fibromyoma Adrenal tumors Meningioma Pheochromocytoma Drugs
Androgens Recombinant erythropoietin Familial (with normal hemoglobin function, Chuvash, erythropoietin receptor mutations) Polycythemia vera Once absolute erythrocytosis has been established, its cause must be determined. An elevated plasma erythropoietin level suggests either a hypoxic cause for erythrocytosis or autonomous erythropoietin production, in which case assessment of pulmonary function and an abdominal CT scan to evaluate renal and hepatic anatomy are appropriate. A normal erythropoietin level does not exclude a hypoxic cause for erythrocytosis. In PV, in contrast to hypoxic erythrocytosis, the arterial oxygen saturation is normal. However, a normal oxygen saturation does not exclude a high-affinity hemoglobin as a cause for erythrocytosis; documentation of previous hemoglobin levels and a family study are important. Other laboratory studies that may aid in diagnosis include the red cell count, mean corpuscular volume, and red cell distribution width (RDW). Only three situations cause microcytic erythrocytosis: β-thalassemia trait, hypoxic erythrocytosis, and PV. With β-thalassemia trait the RDW is normal, whereas with hypoxic erythrocytosis and PV, the RDW is usually elevated due to iron
deficiency. In many patients, the LAP level is also increased, as is the uric acid level. Elevated serum vitamin B12 or B12-binding capacity may be present. In patients with associated acid-peptic disease, occult gastrointestinal bleeding may lead to presentation with hypochromic, microcytic anemia. A bone marrow aspirate and biopsy provide no specific diagnostic information since these may be normal or indistinguishable from ET or IMF, and unless there is a need to establish the presence of myelofibrosis or exclude some other disorder, these procedures need not be done. Although the presence of a cytogenetic abnormality such as trisomy 8 or 9 or 20q– in the setting of an expanded red cell mass supports a clonal etiology, no specific cytogenetic abnormality is associated with PV, and the absence of a cytogenetic marker does not exclude the diagnosis.