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Polycythemia  or Erythrocytosis                  Relative Polycythemia  |  Polycythemia Vera                     

Polycythemia ("many cells") describes an increase in the total quantity or volume (mass) of red blood cells in the body, without any implication regarding leukocytes or platelets.

Erythrocytosis refers to an increase in the concentration of erythrocytes, however, whether measured as number of cells, hemoglobin, or packed cell volume (hematocrit). Erythrocytosis may be the result of

• an increase in the red cell volume or mass (polycythemia, also called absolute erythrocytosis), or
• a reduced plasma volume (called relative or spurious polycythemia or erythrocytosis), which produces an increase in red cell concentration that does not reflect an increase in the quantity of red cells in the body.

Polycythemia (rubra) vera is a myeloproliferative disorder associated with trilineage marrow hyperplasia and characterized by an increased red cell mass, usually in association with leukocytosis and thrombocytosis.

SX:

• thrombosis in patients with polycythemia vera [2] and
• hypertension in relative polycythemia
• the "ruddy cyanosis"
• Headache, dizziness, tinnitus, a full feeling in the head, and a bleeding tendency
• These symptoms usually are relieved by normalization of the hematocrit.

Classification of Erythrocytosis

1. Relative erythrocytosis or polycythemia (pseudoerythrocytosis)

• Hemoconcentration
• Spurious polycythemia (Gaisbock syndrome)

2. Polycythemia (absolute erythrocytosis)

3. Polycythemia vera

4. Secondary polycythemia

5. Secondary to decreased tissue oxygenation (physiologically appropriate polycythemia or hypoxic erythrocytosis)

• High-altitude erythrocytosis (Monge disease)
• Pulmonary disease: Chronic cor pulmonale, Ayerza syndrome, Cyanotic congenital heart disease
• Hypoventilation syndromes:
  • Primary alveolar hypoventilation
  • Pickwickian syndrome, Ondine curse
  • Positional desaturation
  • Sleep apnea
• Abnormal hemoglobins
  • Inherited
  • Acquired: drugs and chemicals, carboxyhemoglobin

6. Secondary to aberrant erythropoietin production or response

• (Physiologically inappropriate polycythemia)
• Tumors, cysts, hemangiomas
• emsp; Androgen abuse
• Erythropoietin abuse

7. Familial polycythemia

8. Idiopathic polycythemia

Treatment:
Phlebotomy can bring about a significant clinical benefit.  When phlebotomy treatments are administered, however, blood volume should not be reduced too greatly at any one time, especially in patients with known arteriosclerotic symptoms (angina pectoris, transient ischemic attacks). This caution is particularly appropriate early in the course of therapy, when hematocrit (and consequent viscosity) are highest. Rather, time should be allowed for hemodilution to occur between phlebotomies; in emergencies, the blood volume should be maintained by infusing saline or some other plasma expander.

Diagnostic Approach to "Suspected Polycythemia Vera" - Mayo Clinic 2-1999

Hgb > 18.5 gm/dL, or a borderline elevated Hgb with any PV related feature, or an interim Hgb increase of > 2 gm/dL

• If No - recheck Hgb in 3 months.
• If Yes - check serum Erythropoietin level
  1. If low serum EPO is confirmed --> Polycythemia Vera
  2. If normal serum EPO:
     •   With PV related features --> obtained bone marrow biopsy.  
          If positive --> Polycythemia Vera 
          If nondiagnostic --> obtain endogenous erythroid colony.  
                 If positive --> Polycythemia Vera.   If negative -- evaluate for secondary erythrocytosis.
     •    Without PV related features --> evaluated for secondary erythrocytosis.  
           If positive --> secondary erythrocytosis.
           If negative --> obtain endogenous erythroid colony.
                 If positive --> Polycythemia Vera.  If negative -- repeat Hgb in 3 months.
  3. If elevated serum EPO --> evaluated for secondary erythrocytosis.

Ref: Mayo Clin Proc, Feb 1999, 74: 159 - Ayalew Refferi

Relative Polycythemia (No elevated red cell mass)        

Approach to erythrocytosis

• No elevated red cell mass --> Relative Polycythemia.
• With elevated red cell mass:
  1. With evidence of myeloprolif. disorder as splenomegaly, leukocytosis, thrombocytosis:
     • If O2 Sat > 92% --> Polycythemia Vera.
     • If O2 Sat < 92% - check BM for hypercellular trilineage hyperplasia.
          If present --> PV.  If nondiagnostic --> check for secondary erythrocytosis.
  2. Without evidence of myeloprolif. disorder as plenomegaly, leukocytosis, thrombocytosisl:
     • If O2 Sat > 92%, and with elevated carboxyhemoglobin --> seondary polycythemia.
       if without elevated carboxyhemoglobin  --> check for family history of erythrocytosis.
       check for Hgb electrophoresis & erythropoietin level studies.  If abnormal - secondary polycythemia.
     • If O2 Sat < 92% --> Secondary polycythemia.

A decrease in plasma volume may produce relative erythrocytosis. The decrease in plasma volume may result from any cause of intravascular fluid loss--insensible fluid loss, persistent vomiting, severe diarrhea, copious sweating, postoperative complications, or shift of fluid into the extravascular space ("third-spacing") or it may be an effect of high altitude. In severe burns, plasma loss leads to hemoconcentration.

Chronic relative polycythemia or erythrocytosis has been variously called Gaisbock syndrome, stress erythrocytosis , benign polycythemia or erythrocytosis, benign erythrocytosis, spurious polycythemia, pseudopolycythemia , or apparent polycythemia. The last three terms are the most accurate: In the absence of an increased red cell mass, there is no polycythemia.
Features reported to be strongly associated with relative polycythemia are stress, obesity, hypertension and smoking ; associations with alcohol abuse and renal disease are occasionally reported. It is probable that this syndrome is not a true clinical entity. The red cell mass values generally accepted as normal at sea level, or at any given altitude, represent the mean ± 2 standard deviations. Thus, on the basis of the normal frequency distribution curve for this physiologic parameter, the values in 2.3% of the population are above this range. The individuals in this group should not be regarded as necessarily abnormal.

The optimum management of relative polycythemia is unknown.
As noted previously, phlebotomy increases cerebral blood flow even in patients with relative polycythemia; whether it is of symptomatic benefit is less clear. It should probably be avoided.

Satisfactory control of hematocrit can be obtained in at least two-thirds of patients by reduction of excess weight, improved hypertension control, avoidance of diuretics, and reduction or cessation of smoking [54] .

Potentially leukemogenic cytoreductive therapy, such as radioactive phosphorus or oral chemotherapeutic agents, is probably never indicated.

See Polycythemia Vera

Ref:
Lee: Wintrobe's Clinical Hematology, 10th ed., Copyright © 1999

12132000