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Overview of Crystal-Induced Arthritides

By Lawrence M. Ryan, MD, Professor of Medicine, Medical College of Wisconsin

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Arthritis can result from intra-articular deposition of crystals:

  • Monosodium urate

  • Ca pyrophosphate dihydrate

  • Basic Ca phosphate (apatite)

  • Rarely, others such as Ca oxalate crystals

Diagnosis requires synovial fluid analysis. Polarized light microscopy is used to specifically identify most crystals; basic Ca phosphate crystals are of ultramicroscopic size and require other methods. Crystals may be engulfed in WBCs or may be extracellular. The presence of crystals does not exclude the possibility of simultaneous infectious or other inflammatory forms of arthritis. Noninvasive identification of monosodium urate and Ca pyrophosphate dihydrate crystals is possible using ultrasonography, but currently few ultrasonographers have sufficient expertise to do this technique.