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| Fig. 16.5 A, Gouty tophi. Tophaceous deposits of gout overlying digits. B, Aspirate from gouty tophus demonstrating diagnostic birefringent gout crystals with polarization. (Courtesy of the Fitzsimons Army Medical Center teaching files.) |
Uric acid crystals in gout are most commonly deposited in the synovium, soft tissues, and skin. The most common site is the synovium of joints, producing acute gouty arthritis. The metatarsophalangeal joint of the great toe is classically involved. Uric acid deposition in the skin and soft tissues results in gouty tophi, which are seen in 20% to 50% of patients. Common sites of involvement include the helix of the ear, elbows, and digits (Fig. 16-5A). These gouty tophi may ulcerate and discharge monosodium urate crystals that appear as a thick chalky material. Under light microscopy, these crystals are needle-shaped and birefringent (Fig. 16-5B).
Thissen CA, Frank J, Lucker GP: Tophi as first clinical sign of gout,
Int J Dermatol 47(Suppl 1):49–51, 2008.
