57. Polycythemias, polyglobulias

The condition where the number of RBCs in the blood is increased has two names, depending on whether it’s primary or secondary. It’s called polycythaemia if it’s primary and polyglobulia if it’s secondary. At least according to POTE. In the international literature, the term polyglobulia is a seldom-used synonym for polycythaemia.

Polycythaemia vera

Polycythaemia vera is a benign myeloproliferative neoplasm in the bone marrow which causes the number of RBC precursors to proliferate wildly. The haematopoietic stem cells have increased sensitivity to EPO, but the EPO levels are low. The characteristics are these:

• RBC count 9 – 10 T/L
• Haematocrit 70%
• Blood viscosity extremely high
• Hypertension
• Capillaries become clogged because of the increased viscosity, decreasing capillary perfusion.
• The sluggish blood flow through the microcirculation gives the tissues more time to extract oxygen. This increases levels of deoxyhaemoglobin, giving cyanosis
• Hepatosplenomegaly
• High risk of thrombosis
• Hyperuricaemia and gout may occur

The treatment involves regular phlebotomy and oral chemotherapy.

Polyglobulia

Polyglobulia is any increase in RBC number due to increased EPO levels in the blood. It’s usually caused by some kind of hypoxia. The increased EPO can either be appropriate for the situation (hypoxia) or inappropriate (normoxia):

• Appropriate EPO release
  • Chronic lung disease
  • Heavy smoking
  • High altitude
  • Congenital cyanotic heart disease
• Inappropriate EPO release
  • Polycystic kidney disease
  • Cushing syndrome (cortisol stimulates EPO)
  • Androgen hyperfunction (androgens stimulate EPO)
  • Paraneoplastic syndromes

The underlying disease should be treated.