In 1961, McCarty and Hollander1 described the presence of monosodium urate crystals in 15 synovial fluids from 18 acute gouty joints. Subsequently McCarty reported the presence of crystals in 141 of 150 fluids in acute gout.
The examination of synovial fluid for urate crystals led to the discovery of a second type of crystal, calcium pyrophosphate dihydrate,2 in fluids from patients experiencing acute arthritis resembling gout. Named "pseudogout," this syndrome represents the clinical and pathologic elaboration of chondrocalcinosis as described roentgenologically by Zitnan and Sitaj.3 The intrasynovial injection of monosodium urate4,5 as well as a variety of other crystals into human and canine joints reproduces many of the clinical aspects of acute gout and pseudogout. The term "crystal induced synovitis" describes the nonspecific inflammatory reaction to microcrystalline irritants.
Compensated polarized microscopy provides a rapid and accurate method for identifying monosodium urate and calcium pyrophosphate crystals in
Phelps P, Steele AD, McCarty DJ. Compensated Polarized Light Microscopy: Identification of Crystals in Synovial Fluids From Gout and Pseudogout. JAMA. 1968;203(7):508–512. doi:10.1001/jama.1968.03140070064014
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