Gout

Gout is an inflammatory arthritis caused by monosodium urate (MSU) crystals that deposit in and around joints, bursae and soft tissue when serum urate stays high over time. Urate is the end product of purine breakdown: the enzyme xanthine oxidase converts hypoxanthine to xanthine and xanthine to uric acid, and the kidneys excrete it. Serum urate rises when production outpaces renal clearance. Allopurinol blocks xanthine oxidase, which is why it lowers urate; uricosuric drugs work differently, by increasing urinary uric acid excretion. When leukocytes meet the crystals, they engulf them and set off an intense local inflammatory response. Leukocytes pour into the joint, which explains the abrupt, severe pain, warmth, redness, swelling and exquisite tenderness of a flare. Colchicine relieves a flare by limiting leukocyte migration and phagocytosis at this step. It is neither an analgesic nor a urate-lowering drug, so it does not stop crystals from accumulating. A flare is the visible consequence of crystal-driven inflammation; it is not a measure of the total crystal burden. Crystals persist after the pain settles. Without sustained urate lowering, the person is...