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Gout and pseudogout (crystal arthropathies)


Gout and pseudogout pathophysiology

  • Gout and pseudogout are crystal arthropathies
  • Crystals of urate (in gout) and calcium pyrophosphate (in pseudogout) are precipitated in joints
  • Neutrophils phagocytose the crystals whilst releasing pro-inflammatory cytokines which trigger attacks
  • Asymptomatic deposition of crystals between attacks is normal; what triggers an attack is unknown


Risk factors for gout (causes of hyperuricaemia)

  • Alcohol
  • Chronic renal disease
  • Hypertension, hyperlipidaemia, diabetes i.e. cardiovascular risk factors (majority of cases)
  • Medications
    • Diuretics, aspirin
  • Malignancy (high cell turnover)
    • Lymphoproliferative and myeloproliferative disorders
  • Certain genetic disorders e.g. G6PD


Risk factors for pseudogout

  • Association with trauma and osteoarthritis
  • Hyperparathyroidism
  • Wilson’s disease
  • Haemochromatosis
  • Loop diuretics causing hypomagnasaemia


Presentation of gout (presents in four ways):

  1. Acute urate synovitis (acute attack of gout – what is mainly covered here).
    • Classically, acute gout affects the first MTP (podagra): initial presentation in 50%.
    • Other joints include ankles, wrists, fingers & knees.
    • Clinical features are sudden onset exquisite tenderness, swelling, redness.
  2. Polyarticular gout
    • Initial presentation in 10%, particularly elderly women
  3. Rheumatoid-like (usually when becomes chronic)
    • May have gouty tophi: smooth, white deposits of uric acid in the skin and around joints
  4. Urate renal stone formation
    • Can precede gout in 15%


Presentation of pseudogout

  • Often similar to gout with acute presentation, but can also be a chronic inflammatory arthritis
  • Typically knees, wrists, ankles, elbows i.e. large joints



Investigations in gout and pseudogout (crystal arthropathies)

  • Always exclude septic arthritis in acutely painful joint
    • Increased risk in, and may co-exist with, crystal arthropathy
  • Joint fluid microscopy
    • Usually need to specifically request crystals (as well as MC&S)
    • Gout: needle-shaped, negatively-birefringent crystals (when viewed under plain polarised light)
      • Positive in about 85% cases
    • Pseudogout: rhomboid, positively-birefringent crystals (when viewed under plain polarised light)
  • Bloods
    • Serum urate
      • May be elevated during an attack, but may also be suppressed (15%)
      • Therefore a normal urate does not exclude gout
    • U&Es:
      • Look for underlying renal impairment
    • Lipids & glucose
  • Plain XR
    • Gout: punched-out lesions, sclerosis and tophi in chronic gout (with preservation of joint space)
    • Pseudogout: chondrocalcinosis (calcification of cartilage)
  • Ultrasound
    • ‘Double contour’ sign in gout: hyperechoic, irregular band over the superficial margin of the articular cartilage (present in over 90%)


Acute treatment of gout and pseudogout (crystal arthropathy)

    • E.g. Naproxen 500mg BD for 2-5 days, then reduce dose
  • Colchicine
    • E.g. Colchicine 5mg BD
    • Higher levels can cause GI upset so start slowly to avoid this
  • In patients who are intolerant of NSAIDs and colchicine (e.g. renal impairment), a short course of oral steroids may be used
    • 40mg od for three days, then taper over 2 weeks
  • Intra-articular steroids may be used in mono-articular attacks


Chronic urate-lowering treatment in gout

  • Lifestyle advice
    • Reduce alcohol, healthy diet, optimise weight, increase activity
  • Treat modifiable risk factors
    • Change diuretics, optimise renal function, treat hyperlipidaemia
  • Allopurinol (xanthine oxidase inhibitor)
    • Indicated in:
      • Recurrent attacks, gouty tophi, urate nephropathy, radiographic changes of gout
    • Do not start during an acute attack as will worsen it
    • Titrate up to maximum tolerated dose (max 900mg/day)
      • Target urate is <300µmol/L
    • Contraindicated in renal failure
    • Small risk of severe allopurinol hypersensitivity reaction
  • Febuxostat (another xanthine oxidase inhibitor)
    • Can be used in patients with renal impairment
    • Indicated in those intolerant to allopurinol/ineffective in maximum tolerated dose


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