Pseudogout

Gout

Gout is a form of microcrystal synovitis caused by the deposition of monosodium urate monohydrate in the synovium. It is caused by chronic hyperuricaemia (uric acid > 450 µmol/l)

Features

Patients typically have episodes lasting several days when their gout flares and are often symptom-free between episodes. The acute episodes typically develop maximal intensity with 12 hours. The main features it presents with are:

• pain: this is often very significant
• swelling
• erythema

Around 70% of first presentations affect the 1st metatarsophalangeal (MTP) joint. Attacks of gout affecting this area were historically called podagra. Other commonly affected joints include:

• ankle
• wrist
• knee

If untreated repeated acute episodes of gout can damage the joints resulting in a more chronic joint problem.

Investigations

Uric acid

• NICE recommends measuring uric acid levels in suspected gout (i.e. in the acute setting)
  • a uric acid level ≥ 360 umol/L is seen as supporting a diagnosis
  • if uric acid level < 360 umol/L during a flare and gout is strongly suspected, repeat the uric acid level measurement at least 2 weeks after the flare has settled

Synovial fluid analysis

• needle shaped negatively birefringent monosodium urate crystals under polarised light

Radiological features of gout include:

• joint effusion is an early sign