Discordance in diagnostic assessment of Achilles tendon thickening between soft X-ray radiography and ultrasonography among patients with coronary artery disease

Achilles tendon (AT) xanthomas are characteristic manifestations of familial hypercholesterolemia (FH). Although soft X-ray radiography (XR) and ultrasonography (US) are used to assess AT thickness, data comparing their diagnostic concordance are limited. We evaluated the correlation and diagnostic agreement between XR and US in measuring AT thickness in coronary artery disease (CAD) patients. We prospectively enrolled CAD patients undergoing AT thickness measurement by XR and US between April 2024 and March 2025. AT thickening was defined according to the 2022 Japan Atherosclerosis Society guideline (XR: ≥8/7.5 mm [male/female], US: ≥ 6/5.5 mm [male/female]). Among 262 patients (14 [5.3%] clinically diagnosed FH), median AT thickness by XR was greater than that by US (7.0 [IQR 6.3-7.6] mm vs. 5.8 [IQR 5.1-6.1] mm, P < 0.001). XR and US measurements were significantly correlated (r = 0.632, P < 0.001). The concordance rate for AT thickening was 83.2% and the discordance (16.8%) was primarily due to XR-/US+ cases (14.9%). In conclusion, although there was a significant correlation between XR and US for AT thickness measurement, discordance in the diagnosis of AT thickening was observed in 17% of patients. Physicians should be aware that US assessment may result in more patients diagnosed with AT thickening than XR.