EXTENDED REPORT

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

Eliseo Pascual¹, Francisca Sivera²

¹ Hospital General Universitario de Alicante, and Universidad Miguel Hernández, Alicante, Spain
² Hospital General Universitario de Alicante, Spain

Correspondence to:
Dr E Pascual
Catedrático de Medicina (Reumatología), Hospital General Universitario de Alicante, Maestro Alonso 109, 03010 Alicante, Spain; pascual_eli{at}gva.es

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.

Abbreviations: MTP, metatarsophalangeal; MSU, monosodium urate; SF, synovial fluid; SUA, serum uric acid

Keywords: gout; monosodium urate crystals; synovial fluid; gout treatment

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