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

Abstract

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/400 x 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 (rs = 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/400 x field, reducing to 3 (1-6.5) crystals/400 x 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.