Gout
A crystal arthritis in which chronically raised urate exceeds its solubility, deposits as monosodium urate crystals in cool peripheral joints and triggers explosive innate inflammation, treated acutely by damping inflammation and long-term by lowering urate.
In a nutshell
Urate exceeds its solubility, precipitates as monosodium urate crystals in cool peripheral joints, and the crystals ignite NLRP3-inflammasome-driven innate inflammation. Treat the attack by damping inflammation; prevent recurrence by lowering urate, and never do both at once.
Classic presentation
A patient wakes in the early hours with an exquisitely painful, red, hot, swollen first metatarsophalangeal joint that peaks within a day, often after alcohol or a thiazide, with previous self-limiting attacks.
Key points
- Gout is a solubility problem before it is an inflammation problem: too much urate, mostly from under-excretion (renal impairment, thiazides, alcohol).
- Crystals form where it is coolest and most peripheral, hence podagra at the first MTP joint, and hence attacks that characteristically begin overnight.
- Joint aspiration with polarised light microscopy is definitive: negatively birefringent needle-shaped crystals, and it excludes septic arthritis.
- Serum urate can be normal or low during an acute attack. Measure it a few weeks after the flare settles.
- Acute treatment is anti-inflammatory (an NSAID, colchicine or a corticosteroid) and does not change the urate level.
- Urate-lowering therapy (a xanthine oxidase inhibitor such as allopurinol) is started later, under anti-inflammatory cover, and titrated to a target urate.
First-line investigation
Joint aspiration with polarised light microscopy: it demonstrates urate crystals and excludes septic arthritis, the dangerous mimic.
First-line management
Damp the inflammation with an NSAID, colchicine or a corticosteroid, chosen on comorbidities. Do not start or stop urate-lowering therapy during the attack.
Exam traps
- A hot swollen joint with fever is septic arthritis until aspirated. Gout is the diagnosis you make after excluding infection, not instead of it.
- A normal serum urate during an acute attack does not exclude gout.
- Do not start allopurinol during a flare, but do not stop it either if the patient is already established on it.
- Any sudden shift in urate, up or down, can mobilise crystals and precipitate a flare. That is why urate-lowering is introduced slowly and with cover.
Educational content pending clinical review. Not medical advice.