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

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 p

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