[Ultrasonography of the first metatarsophalangeal joint in gout]

About one half of the first gout attacks occur in the first metatarsophalangeal joint (MTPJ1); in the disease course this joint is practically inevitably affected. Radiographic evidence of bone erosions is the indication for hypouricaemic therapy in order to prevent joint destruction and nephropathy. Advantages of ultrasonography (US) comparing to conventional x-ray findings in depicting early bone erosions in various inflammatory arthropathies have been demonstrated by several studies.

The aims of this study were to compare US and x-ray findings in the detection of MTPJ1 erosions in patients with gout, to correlate sonographic and clinical features, and to detect possible characteristic sonographic features of gout.

Thirty patients (60 MTPJ1) with primary gout (ACR) and 10 age-matched control subjects (20 MTPJ1) with different inflammatory arthropathies were clinically evaluated. Standard dorsiplantar weight bearing and lateral weight bearing x-ray views of both feet were taken. US was performed and interpreted by an independent sonographer on the presence of bone erosions, synovial fluid, synovial hypertrophy, Doppler signal and hyperechoic spots. Statistical analysis was performed (Spearman and Pearson correlation coefficient, Wilcoxon and chi2 test.)

Twenty-four studied MTPJ1 had evidence of erosions, 17 only on US and seven both on x-ray and on US (Z = -4.123; p = 0.000). US findings showed that hyperechoic spots were the most prominent feature of gouty MTPJ1 (chi2 = 40.909; p = 0.000), followed by erosions and synovial fluid presentation.

US of MTPJ1 in gout discovers significantly more erosions than x-ray, which may have therapeutic implications. The evidence of hyperechoic spots (surrogate crystals) of the different size, number and orientation is a major sonographic feature of the MTPJ1 in gout, which may be of importance in the diagnosis of certain cases (low serum urate, unavailable synovial fluid or the urate crystals absence).