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In an article published in Annals of the Rheumatic Diseases, Chowalloor et al1 suggested, based on a literature review, that ultrasonography (US) is a promising tool that could be used in the diagnosis and management of gout. In this letter, we wish to add further data to Chowalloor et al's conclusion. We have performed a meta-analysis (up to July 2012) to investigate the frequency of ultrasonographic signs, that is, joint effusion, synovitis, bone erosion, tophi and double contour (DC), in gout and asymptomatic hyperuricaemia compared with controls (figure 1).
We searched MEDLINE to identify all reports of interest published prior to July 2012 using the following search terms: (“echography”[tiab] OR “sonography”[tiab] OR “ultrasonography”[tiab] OR “US”[tiab]) and (“gout”[tiab] OR “urate”[tiab] OR “uric acid”[tiab]). We retrieved a total of 195 articles. In addition, we searched for congress abstracts from the annual scientific meetings held by the French Society for Rheumatology, European League Against Rheumatism and American College of Rheumatology between 2008 and 2012 using the terms ‘echography’ and ‘gout’. Comprehensive Meta-analysis (V.2, BioStat Corporation) was used to conduct the meta-analytic statistical analysis.2 Heterogeneity in the study results was evaluated by examining forest plots, CIs and formal tests for homogeneity based on the I2 statistics. Random effects meta-analyses were conducted when data could be pooled.
After reading the title, abstract and full text of all articles, we retained eight, along with four abstracts, involving a total of 446 patients with gout, 102 with asymptomatic hyperuricaemia and 249 controls. The prevalence of ultrasonographic signs in patients with gout is summarised in table 1. In patients with asymptomatic hyperuricaemia and controls, data were only available and analysed for a DC sign that was reported in one healthy control. Pineda found this sign in 42 joints (42/200, 21%) in asymptomatic hyperuricaemia and Howard in just 8.8% of joints (6/68).3 ,4
Our study results provide information that reinforces the conclusion of Chowalloor et al, who suggested that US is useful in the diagnosis of gout. However, not all sonographic signs have the same importance in this diagnosis. Joint effusion and synovitis are not very specific whereas a DC sign or tophus, especially in the first metatarsal joint, points more towards gout. Naredo et al5 recently confirmed the importance of looking for DC signs in the first metatarsal.
The diagnosis of gout is confirmed by the microscopic demonstration of monosodium urate crystals in synovial fluid analysis. In the absence of joint effusion or to support the diagnosis, joint and cartilage US, especially in the first metatarsal joint, is indeed very useful.
Contributors Conceived and designed the experiments: SM BP MC and MS. Performed the experiments: SM. Analysed the data: SM and BP. Wrote the paper: SM BP MC and MS.
Competing interests None.
Provenance and peer review Not commissioned; externally peer reviewed.