Gout

 

• Background

  Pathophysiology

  • Hyperuricaemia → monosodium urate crystal deposits in or around joints.
  • Can be primary – possibly genetic – or secondary to one of the risk factors listed below.

  Epidemiology

  • UK prevalence 1/40.

• Signs and symptoms

  • Acute monoarthritis: hot, red, swollen, painful joint. May be immobile.
  • Often affects 1st MTP. Can also affect any large or small joints of the limbs, and can be polyarticular.
  • Tophi in chronic disease: hard white lumps (crystals) on peripheries e.g. fingers, toes, ears.

• Risk factors

  Primary gout:

  • Male sex.
  • Family history.

  Secondary gout:

  • Lifestyle: alcohol, ↑dietary purines (e.g. red meat).
  • Drugs: diuretics, cytotoxics.
  • Diseases: diabetes, hypertension, hypertriglyceridaemia, kidney failure, leukaemia.
  • Rapid weight loss.

• Investigations

  • Diagnosis can be clinical, but aspirate joint to confirm and/or if there is any suspicion of septic arthritis. Aspirate will show negatively birefringent needle-shaped urate crystals under light microscopy.
  • ↑Serum urate, but only 70% sensitive. More reliable if done 4 weeks after resolution of attack.
  • X-ray: soft-tissue swellings early, and punched out periarticular erosions later.
  • Screen for diabetes and hyperlipidaemia after the attack.

• Management

  Acute

  Medical:

  • 1st line: NSAIDs or colchicine. Colchicine is a microtubule inhibitor that prevents mitosis; diarrhoea and vomiting are common side effects.
  • 2nd line: steroids, PO or intra-articular.

  Rest and elevate affected join.

  Long-term

  Medical prophylaxis with a xanthine-oxidase inhibitor:

  • 1st line: allopurinol.
  • Indications: recurrent (≥2 attacks), complications (tophi, stones, kidney disease), or patient on diuretics.
  • Traditional advice is to start 2 weeks after attack has settled, due to theoretical risk of worsening the attack, and giving NSAID or colchicine cover until then. However, recent studies suggest starting during the acute attack is safe and may simplify treatment, with the downside of making diagnosis more difficult by reducing the urate elevation.
  • It should be continued during an attack for patients already on it.
  • 2nd line: febuxostat.

  Lose weight and reduce dietary purines.

• Complications

  Renal disease:

  • Stones
  • Interstitial nephritis.

• Allopurinol

  Mechanism

  Inhibits xanthine oxidase, preventing conversion of xanthine into uric acid.

  Contraindications

  Hypersensitivity to allopurinol.

  Side effects

  • Nausea and vomiting.
  • Rash
  • Kidney failure.