Sunday, 12 September 2010

MRCP revision battle 9.2: Gout

Ah Gout... that classical disease of red-faced old men...

In terms of MRCP, you need to expand the above knowledge to include the following...

Gout usually presents as a single, swollen, hot, painful joint.  If the joint affected is the big toe, it is called a podagra.

Microscopy of joint fluid would reveal negatively birefrigent needle-shaped monosodium urate crystals.

Uric acid may be >450micromols - but equally may be normal in an acute attack.

CRP is usually raised, but if the question shows a raised WCC too start thinking about different diagnoses, for example septic arthritis.

Gout may be either primary or secondary.

Primary gout may be:
  • idiopathic - usually due to decreased excretion of uric acid 
  • associated with Lesch-Nyhan Syndrome (to be covered in a very brief battle tomorrow)

Secondary gout can broadly be divided into things which cause increased production/intake of urate, and things which decrease its excretion.

Causes of increased production/intake include:
  • myeloproliferative/lymphoproliferative disorders
  • psoriasis
  • cytotoxic drugs
  • food - beer, yeast, seafood, liver, kidney
  • exercise
  • fits
  • acidosis

Causes of decreased excretion include:
  • renal failure
  • diuretics
  • low dose aspirin
  • alcohol
  • lead poisoning

XR should show a normal joint space (may be decreased in late disease) and large punched-out erosions distant from the joint margins.

Treatment is NSAIDs - if these are contraindicated, colchine can be used.

Prophylaxis is with allopurinol (a xanthine oxidase inhibitor).  It should be started 2 to 3 weeks after an acute attack if:
  • >1 attack
  • tophi present
  • renal disease
  • urate stones
  • Lesch-Nyhan syndrome
  • cytotoxic drugs used (in which case it should be given before any episodes of gout)

So after that quick whizz through gout, lets embrace is near-cousin pseudo-gout...