The first thing to establish is if the polycythaemis is 'true/absolute' or 'relative/pseudo'.
Relative/pseudo polycythaemia occurs due to decreased plasma volume. This may occur due to dehydration (eg vomiting, diarrhoea, diuretics)
A special form of relative polycythaemia is Gaisbocks. This tends to affect middle-aged men and is attributed to stress (hypertension, smoking, mild obesity) causing a chronically reduced plasma volume.
True/absolute polycythaemis is due to raised red cell mass.
It can be further divided into primary true polycythaemia and secondary true polycythaemia.
Primary true polycythaemia = polycythaemia rubra vera
Polycythaemia rubra vera is associated with JAK2 mutation in 95% of cases.
It peaks in the 6th decade.
Features include:
- hyperviscosity-syndrome symptoms
- pruritis, especially after a hot bath
- splenomegaly
- plethoric features
- hypertension in 1/3
- haemorrhage secondary to abnormal platelets
- DVTs/arterial thrombosis
- peptic ulceration
- gout
WCC/platelets/neutrophil alkaline phosphatase are raised; this helps distinguish primary from secondary polycythaemia.
Secondary polycythaemia
Secondary polycythaemia is due to raised erythropoietin.
Causes:
- physiological - neonates, high altitude
- congenital cyanotic heart disease
- smoking/COPD
- HbM
- renal cysts
- post renal transplant
- fibroids
- hepatoma
Management of true polycthaemia is:
- venesection
- hydroxyurea to supress erythropoesis
- aspirin
Now for something completely different - levels of evidence...
