Monday, 18 October 2010

MRCP revision battle 33.6: Polycythaemia

Polycythaemia is a raised red cell count and haemocrit, defined as >0.52 in males or >0.48 in females.

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.

  • 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...