Gout

Gout is an inflammatory arthritis caused by deposition of monosodium urate (MSU) crystals in and around a joint. Crystals form when serum urate remains above its saturation point, usually because the kidneys cannot excrete enough urate or, less often, because production is increased. The crystals themselves are not painful until the immune system reacts to them. Phagocytosis of MSU crystals activates the NLRP3 inflammasome and releases inflammatory mediators, including interleukin-1β. Neutrophils then enter the joint, producing the abrupt swelling, erythema, warmth, and exquisite pain of an acute flare. Repeated inflammation can eventually produce tophi, chronic joint damage, and persistent functional limitation. The classic site is the first metatarsophalangeal joint of the great toe, called podagra. The ankle, knee, midfoot, and other peripheral joints can also be affected. A flare is usually monoarticular and develops rapidly, often becoming severe over several hours.