The value of ankle inclusion in ultrasound screening for crystal deposits and inflammation in asymptomatic hyperuricemia.

OBJECTIVE

This study evaluated whether extending the conventional Stewart ultrasound protocol to include the ankle (ankle-inclusive protocol) improves monosodium urate (MSU) crystal detection in asymptomatic hyperuricemia (AH), compared to further extension with the second metatarsophalangeal joint (MTP2-extended protocol), and whether quantitative crystal burden correlates with subclinical inflammation.

METHODS

In this retrospective single-center study, 94 adults with AH and with no history of clinical gout underwent three ultrasound protocols: Stewart (knees, MTP1), ankle-inclusive (knees, MTP1, ankles), and MTP2-extended (knees, MTP1, ankles, MTP2). MSU crystals and Power Doppler (PD) signals were defined per OMERACT 2021. A novel ankle crystal load score (crystal_score) was developed. Statistical analyses included McNemar's test, ROC analysis, and multivariable logistic regression.

RESULTS

Adding ankle assessment to the Stewart protocol significantly increased MSU crystal detection by 14.9% (85.1% vs. 70.2%, p < 0.001), whereas subsequent MTP2 addition provided no significant gain (4.3%, p = 0.125). Of the 14 cases detected solely by ankle assessment, the majority (85.7%, 12/14) belonged to the high-risk subgroup (serum uric acid [SUA] ≥ 480 μmol/L), and 28.6% (4/14) exhibited PD signals at the ankle. The crystal_score demonstrated significant discriminative ability for subclinical inflammation (AUC = 0.677, p = 0.003) and was an independent predictor after adjustment (adjusted OR = 1.16 per unit, p = 0.001), particularly in patients with SUA < 480 μmol/L (AUC = 0.709, p = 0.013).

CONCLUSION

Ankle ultrasonography significantly improves MSU crystal detection in AH and should be integrated into screening protocols. The crystal_score has significant discriminative ability as a quantifiable biomarker for subclinical inflammation, especially in patients with SUA < 480 μmol/L, with its moderate correlation (Spearman's ρ = 0.333) reflecting the "silent deposition" phase of AH. MTP2 assessment can be omitted.These findings support standardized, risk-stratified ultrasound workflows for AH management.