Polycythaemia

Specialties > Haematology

Background knowledge 🧠

Definition

Polycythaemia refers to an increased red blood cell mass in the body.
It is generally defined as a haemoglobin concentration >185 g/L in men and >165 g/L in women.
It can be primary (due to bone marrow pathology) or secondary (due to external factors).

Epidemiology

Polycythaemia is relatively rare, with an incidence of about 2-3 per 100,000 people annually.
More common in men than women.
Primary polycythaemia (Polycythaemia vera) typically presents in middle age (50-70 years).
Secondary polycythaemia is more prevalent and can occur at any age depending on the underlying cause.

Aetiology and Pathophysiology

Primary polycythaemia (Polycythaemia vera) is caused by a mutation in the JAK2 gene leading to unregulated red blood cell production.
Secondary polycythaemia results from increased erythropoietin (EPO) production due to hypoxia, tumours, or other causes.
Hypoxic causes include chronic lung disease, smoking, and living at high altitude.
Non-hypoxic causes include renal disease, hepatic tumours, and paraneoplastic syndromes.

Types

Polycythaemia Vera (Primary Polycythaemia): Characterised by the overproduction of red blood cells due to a bone marrow disorder.
Secondary Polycythaemia: Caused by external factors like hypoxia or tumours leading to increased EPO.
Relative Polycythaemia: Apparent increase in red blood cells due to decreased plasma volume, often due to dehydration or diuretics.

Clinical Features 🌡️

Symptoms

Headaches and dizziness.
Pruritus, especially after a hot shower (common in Polycythaemia vera).
Visual disturbances.
Fatigue and weakness.
Dyspnoea.
Night sweats and weight loss (more specific to Polycythaemia vera).

Signs

Plethora (ruddy complexion).
Hypertension.
Splenomegaly (particularly in Polycythaemia vera).
Gout (due to increased cell turnover).
Erythromelalgia (burning pain in hands/feet).
Thrombosis or bleeding complications.

Investigations 🧪

Tests

Full blood count (FBC): Elevated haemoglobin, haematocrit, and red cell mass.
Serum erythropoietin levels: Low in Polycythaemia vera, high in secondary polycythaemia.
JAK2 mutation analysis: Positive in over 95% of Polycythaemia vera cases.
Oxygen saturation: To exclude hypoxic causes.
Abdominal ultrasound: To check for splenomegaly and rule out renal causes.
Bone marrow biopsy: May be performed to assess bone marrow cellularity in unclear cases.

Management 🥼

Management

Venesection: First-line treatment in Polycythaemia vera to reduce red cell mass.
Aspirin: Low-dose aspirin to reduce thrombotic risk.
Cytoreductive therapy: Hydroxycarbamide (hydroxyurea) is used in high-risk patients.
Treat underlying cause in secondary polycythaemia (e.g., oxygen therapy for hypoxia).
JAK inhibitors: For patients with Polycythaemia vera resistant to first-line treatments.

Complications

Thrombosis: Increased risk of both arterial and venous thrombosis.
Myelofibrosis: A potential progression of Polycythaemia vera.
Acute leukaemia: Rare, but possible transformation from Polycythaemia vera.
Bleeding complications: Paradoxical risk due to platelet dysfunction.
Gout: Due to increased uric acid from cell turnover.

Prognosis

Polycythaemia vera is a chronic condition with variable prognosis.
With treatment, patients can live for many years but require ongoing monitoring.
Risk of complications (e.g., thrombosis, myelofibrosis) impacts overall prognosis.
Survival rates have improved with better management strategies.

Key Points

Polycythaemia involves an increased red blood cell mass and can be primary or secondary.
Key diagnostic tests include FBC, JAK2 mutation analysis, and serum EPO levels.
Management focuses on reducing red cell mass and preventing complications, particularly thrombosis.
Polycythaemia vera is associated with specific complications like myelofibrosis and acute leukaemia.
Regular follow-up is crucial to monitor disease progression and manage complications.

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