Time required for disappearance of urate crystals from synovial fluid after successful hypouricaemic treatment relates to the duration of gout.

OBJECTIVES To determine whether hypouricaemic treatment results in the disappearance of urate crystals from gouty joints and to define the time required. METHODS In 18 patients with monosodium urate (MSU) crystal proven gout, and after the initiation of successful serum uric acid (SUA)-lowering treatment, an arthrocentesis of the asymptomatic signal joint (11 knees, 7 first metatarsophalangeal joints) was performed every 3 months to obtain a synovial fluid (SF) sample. The sample was then analysed for the presence of MSU crystals, and the number of crystals/400x field was noted. SUA levels and the duration of gout were also noted. RESULTS MSU crystals disappeared from the SF of all 18 joints after reduction of SUA to normal levels. The time required for disappearance ranged from 3 to 33 months; disappearance time correlated with the duration of gout (r(s) = 0.71; p<0.01). The median number of MSU crystals in the SF samples before urate-lowering treatment was 7.5 (2.5-11) crystals/400x field, reducing to 3 (1-6.5) crystals/400x field (p<0.05) at 3 months. Crystal counts continued to decrease after 3 months. CONCLUSIONS In gout, reduction of SUA to normal levels results in disappearance of urate crystals from SF, requiring a longer time in those patients with gout of longer duration. This indicates that urate crystal deposition in joints is reversible. Normalisation of SUA levels results in a decrease in the concentration of MSU crystals in SF in the asymptomatic gouty joints. This may partially explain the reduced frequency of gouty attacks when a patient has been treated with SUA-lowering drugs.