Polycythemia Vera Erythremic Polycythemia and Erythrocytosis

Increases in erythrocytes, hemoglobin, and hematocrit above the normal range due to causes unrelated to hematopoiesis (i.e., the majority of cases) are referred to as secondary erythrocytosis or secondary polycythemia. However, it should be remembered that the "normal" range of values is quite wide, especially for men, in whom the normal range can be as much as 55% of the hematocrit!

Table 28 Causes of secondary erythrocytosis

Reduced O2 transport capacity

- Carboxyhemoglobin formation in chronic

smokers

- High altitude hypoxia, COPD

- Heart defect (right-left shunt)

- Hypoventilation (e. g., obesity hypoventilation)

Reduced O2 release from hemoglobin

- Congenital 2,3-diphosphoglycerate deficiency

Renal hypoxia

- Hydronephrosis, renal cyst

- Renal artery stenosis

Autonomous erythropoietin biosynthesis

- Renal carcinoma

- Adenoma

COPD = Chronic obstructive pulmonary disease

COPD = Chronic obstructive pulmonary disease

An autonomous increase in erythropoiesis, i.e., polycythemia vera, represents a very different situation. Polycythemia vera—which one might call a "primary erythrocytosis"—is a malignant stem cell abnormality of unknown origin and is a myeloproliferative syndrome (p. 112). Leukocyte counts (with increased basophils) and thrombocyte counts often rise simultaneously, and a transition to osteomyelosclerosis often occurs in the later stages.

Revised Criteria for the Diagnosis of Polycythemia Vera (according to Pearson and Messinezy, 1996)

— A1 elevated erythrocyte numbers

— A2 absence of any trigger of secondary polycythemia

— A3 palpable splenomegaly

— A4 clonality test, e.g., PRV-1 marker (polycythemia rubra vera 1 )

— B3 splenomegaly (sonogram)

— B4 endogenous erythrocytic colonies

Diagnosis in the presence of: A1 + A2 + A3/A4 or A1 + A2 + 2 x B

Bone marrow cytology shows increased erythropoiesis in both poly-cythemia vera and secondary polycythemia. Polycythemia vera is the more likely diagnosis when megakaryocytes, granulopoiesis, basophils, and eosinophils are also increased.

I Bone marrow analysis contributes to the differential diagnosis between secondary erythrocytosis and polycythemia vera

Polycythemia Vera

Fig. 58 Polycythemia vera and secondary erythrocytosis. a In reactive secondary erythrocytosis there is usually only an increase in erythropoiesis. b In polycythemia vera megakaryopoiesis (and often granulopoiesis) are also increased. c Bone marrow smear at low magnification in polycythemia vera, with a hyperlobulated megakaryocyte (arrow). d Bone marrow smear at low magnification in polycythemia vera, showing increased cell density and proliferation of megakaryocytes. e In polycythemia vera, iron staining shows no iron storage particles.

Fig. 58 Polycythemia vera and secondary erythrocytosis. a In reactive secondary erythrocytosis there is usually only an increase in erythropoiesis. b In polycythemia vera megakaryopoiesis (and often granulopoiesis) are also increased. c Bone marrow smear at low magnification in polycythemia vera, with a hyperlobulated megakaryocyte (arrow). d Bone marrow smear at low magnification in polycythemia vera, showing increased cell density and proliferation of megakaryocytes. e In polycythemia vera, iron staining shows no iron storage particles.

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