Polycythaemia

Definition | Aetiology | Pathophysiology | Risk Factors | Signs and Symptoms | Investigations | Management

Definition

Polycythaemia refers to an increased red blood cell mass, leading to raised haematocrit and haemoglobin levels. It is classified into primary polycythaemia (polycythaemia vera) and secondary polycythaemia.

Aetiology

  • Primary polycythaemia: polycythaemia vera, a myeloproliferative disorder caused by JAK2 mutation.
  • Secondary polycythaemia: chronic hypoxia (e.g., chronic lung disease, high altitude, congenital heart disease).
  • Erythropoietin-driven: renal tumours, hepatocellular carcinoma, exogenous erythropoietin use.
  • Relative polycythaemia: due to plasma volume contraction in dehydration or diuretic use.

Pathophysiology

  • In polycythaemia vera, uncontrolled erythropoiesis occurs due to JAK2 mutation, leading to increased red cell mass.
  • In secondary polycythaemia, chronic hypoxia stimulates erythropoietin production, promoting erythropoiesis.
  • Increased blood viscosity contributes to thrombotic complications.

Risk Factors

  • Chronic lung disease.
  • Obstructive sleep apnoea.
  • Congenital heart disease.
  • High altitude exposure.
  • JAK2 gene mutation (in polycythaemia vera).
  • Smoking.

Signs and Symptoms

  • Headaches, dizziness.
  • Pruritus, especially after hot showers (histamine release).
  • Facial plethora (ruddy complexion).
  • Erythromelalgia (burning pain in hands and feet).
  • Splenomegaly (common in polycythaemia vera).
  • Increased risk of thrombosis (DVT, stroke, MI).

Investigations

  • Full blood count (FBC): raised haemoglobin and haematocrit.
  • JAK2 mutation analysis: confirms polycythaemia vera.
  • Erythropoietin levels: low in polycythaemia vera, high in secondary polycythaemia.
  • Arterial blood gas (ABG): checks for hypoxia in secondary polycythaemia.
  • Renal ultrasound: assesses for erythropoietin-secreting tumours.

Management

1. General Measures:

  • Address underlying cause (e.g., oxygen therapy for hypoxia-related polycythaemia).
  • Avoid dehydration.
  • Smoking cessation.

2. Specific Treatment:

  • Polycythaemia vera: regular venesection to maintain haematocrit <45%.
  • Low-dose aspirin: reduces thrombotic risk.
  • Hydroxycarbamide: cytoreductive therapy for high-risk patients.
  • Ruxolitinib: JAK2 inhibitor for refractory cases.

3. Referral:

  • Haematology: for suspected polycythaemia vera or unexplained polycythaemia.
  • Respiratory: if secondary polycythaemia is due to chronic hypoxia.
  • Nephrology: if renal pathology is suspected.
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