TRANSITIONAL URATE CRYSTALS: A FACTOR IN GOUTY ARTHRITIS?: 191

Abstract

Apparent crystal-negative effusions are sometimes seen in the early course of acute gouty arthritis. Also, newly-prepared urate crystals become less phlogistic after heating in vitro. A plausible explanation for these phenomena lies in the tendency for some solutes to precipitate first as unstable hydrated crystals which then evolve into more stable but less hydrated forms. Polyhydrated urate salts could be intensely phlogistic yet non-birefringent in polarized light. We examined this hypothesis after finding only needle-shaped, non-birefringent, intracellular objects up to 15 microns long in a gouty synovial fluid.

A supersaturated urate solution (500 mg/dl) was prepared in 0.1 N NaOH at 90°, allowed to cool, neutralized to pH 7.2 with HC1, and incubated at 37°. Serial observations and photographs of this solution revealed a mixed population of crystals including rod-like structures which appeared after 60 minutes and became more birefringent over time. This transition sometimes occurred uniformly, but more often progressed from individual foci within the crystal. Heating for 2 hours at 190° converted all crystals to a strongly birefringent form.

For 25 years, monosodium urate monohydrate has been accepted as "the gout culprit." It now seems possible, however, that one or more polyhydrated, transitional form(s) of urate may also participate in the acute inflammatory process. Further, such crystals may be missed by polarized light microscopy.

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