Makindo Medical Notes

🌡️ Polycythaemia = an abnormally raised red blood cell (RBC) mass, leading to increased blood viscosity. It may be true (increased RBC production) or apparent (reduced plasma volume). ⚠️ Important because it predisposes to thrombosis, haemorrhage, and progression to myelofibrosis/leukaemia.

🧬 Pathophysiology

• Primary (Polycythaemia Vera, PV): Myeloproliferative neoplasm, usually due to JAK2 mutation → uncontrolled RBC production, often with ↑ WBC and platelets.
• Secondary: Driven by ↑ erythropoietin (EPO) due to hypoxia (lung disease, high altitude, cyanotic heart disease) or EPO-secreting tumours (renal/hepatic carcinoma).
• Relative (Apparent): Normal RBC mass but ↓ plasma volume → dehydration or stress-related polycythaemia (Gaisböck syndrome).

📋 Causes

🩺 Clinical Features

• Hyperviscosity ➝ headache, confusion, blurred vision, TIAs
• Thrombosis ➝ DVT, PE, stroke, MI
• Haemorrhage (paradoxical, due to abnormal platelets)
• Aquagenic pruritus (PV hallmark)
• Plethoric, ruddy complexion & splenomegaly

🔎 Investigations

• Repeat FBC – confirm ↑ Hb/Hct
• Blood film – exclude leukaemia (look for ↑ WCC, platelets)
• JAK2 mutation – confirms PV
• EPO levels – low in PV, high in secondary causes
• Bone marrow biopsy – hypercellular in PV
• ABG/oximetry – hypoxia in lung/cardiac disease
• CXR – emphysema, lung pathology
• USS abdo/pelvis – exclude renal/hepatic tumours
• U&E, uric acid – renal function and gout risk

💊 Management Overview

• PV: Regular venesection, aspirin, hydroxyurea/ruxolitinib for high-risk
• Secondary (lung disease): Oxygen, treat underlying cause, venesection if needed
• Tumour-related: Treat malignancy, venesection if symptomatic
• Relative: Rehydration or lifestyle modification
• ⚠️ Always address cardiovascular risk (BP, smoking, diabetes, statins if needed)

💡 Teaching Pearl: Polycythaemia vera = JAK2+, low EPO, splenomegaly, aquagenic pruritus. Secondary = high EPO, often hypoxia or tumour. Relative = normal RBC mass, ↓ plasma volume.