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.
- hyperviscosity-syndrome symptoms
- pruritis, especially after a hot bath
- plethoric features
- hypertension in 1/3
- haemorrhage secondary to abnormal platelets
- DVTs/arterial thrombosis
- peptic ulceration
WCC/platelets/neutrophil alkaline phosphatase are raised; this helps distinguish primary from secondary polycythaemia.
Secondary polycythaemia is due to raised erythropoietin.
- physiological - neonates, high altitude
- congenital cyanotic heart disease
- renal cysts
- post renal transplant
Management of true polycthaemia is:
- hydroxyurea to supress erythropoesis
Now for something completely different - levels of evidence...