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

DiagnosisWhen 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) 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 presentwith an elevated hemoglobin or hematocrit alone, or with thrombocytosis alone,the diagnostic evaluation is more complex because of the many diagnosticpossibilities (Table 103-2). Furthermore, unless the hemoglobin level is ≥20 gm%(hematocrit ≥60%), it is not possible to distinguish PV from disorders causingplasma volume contraction. Uniquely in PV, an expanded plasma volume canmask an elevated red cell mass; thus, red cell mass and plasma volumedeterminations are mandatory to establish the presence of an absoluteerythrocytosis and to distinguish this from relative erythrocytosis due to areduction in plasma volume alone (also known as stress or spurious erythrocytosisor Gaisböcks syndrome). This is true even in with the discovery of the JAK2V617F mutation, because not very patient with PV expresses this mutation, whilepatients without PV do. Figure 58-18 illustrates a diagnostic algorithm for theevaluation 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 diseaseRenal disease Renal artery stenosis Focal sclerosing or membranous glomerulonephritis Renal transplantationTumors Hypernephroma Hepatoma Cerebellar hemangioblastoma Uterine fibromyoma Adrenal tumors Meningioma PheochromocytomaDrugs Androgens Recombinant erythropoietin Familial (with normal hemoglobin function, Chuvash, erythropoietinreceptor mutations) Polycythemia vera Once absolute erythrocytosis has been established, its cause must bedetermined. An elevated plasma erythropoietin level suggests either a hypoxiccause for erythrocytosis or autonomous erythropoietin production, in which caseassessment of pulmonary function and an abdominal CT scan to evaluate renal andhepatic anatomy are appropriate. A normal erythropoietin level does not exclude ahypoxic cause for erythrocytosis. In PV, in contrast to hypoxic erythrocytosis, thearterial oxygen saturation is normal. However, a normal oxygen saturation doesnot 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 cellcount, mean corpuscular volume, and red cell distribution width (RDW). Onlythree situations cause microcytic erythrocytosis: β-thalassemia trait, hypoxicerythrocytosis, and PV. With β-thalassemia trait the RDW is normal, whereas withhypoxic erythrocytosis and PV, the RDW is usually elevated due to irondeficiency. In many patients, the LAP level is also increased, as is the uric acidlevel. Elevated serum vitamin B12 or B12-binding capacity may be present. Inpatients with associated acid-peptic disease, occult gastrointestinal bleeding maylead to presentation with hypochromic, microcytic anemia. A bone marrow aspirate and biopsy provide no specific diagnosticinformation since these may be normal or indistinguishable from ET or IMF, andunless there is a need to establish the presence of myelofibrosis or exclude someother disorder, these procedures need not be done. Although the presence of acytogenetic abnormality such as trisomy 8 or 9 or 20q– in the setting of anexpanded red cell mass supports a clonal etiology, no specific cytogeneticabnormality is associated with PV, and the absence of a cytogenetic marker doesnot exclude the diagnosis.