Quantitative ultrasound skin thickness measurement for assessment of lower-limb lymphedema

A previous study demonstrated that ultrahigh frequency ultrasound can be used to assess upper-limb lymphedema by measuring skin thickness. The aim of this study was to establish skin thickness cut-off values using conventional high-frequency ultrasound (HFUS) for lower limb lymphedema.

Skin thickness was measured at 10 points in the lower limbs of 20 healthy volunteers and 20 patients with lower limb lymphedema using HFUS (15 MHz). Measurements were statistically compared between the groups and with the indocyanine-green lymphography findings. A multivariable linear model and ROC curve analysis were also performed to establish cut-off values.

Skin thickness was significantly greater in lymphedematous limbs than in controls (p < 0.001). Mean examination time was 5 min per patient. Cut-off values at each point were established to identify lymphedema with a specificity of 100% and sensitivity of 70-95%. The medial ankle was the most informative site, with a cut-off value of 2 mm (sensitivity 95% and specificity 100%). Based on the results, a practical algorithm was proposed: values <1.95 mm at all points were not suggestive of lymphedema; any value ≥2.3 mm was highly suggestive of lymphedema; intermediate values (1.95-2.3 mm) required point-specific interpretation or confirmatory imaging. Using this approach, ultrasound was used to identify subclinical contralateral lymphedema in 4 patients (20%), ultrasound + ICG-L in 3 additional patients (15%), and only 6 limbs (7.5%) required confirmatory imaging.

Point-based skin-thickness measurement using HFUS is useful in detecting and assessing lymphedema, including early or subclinical stages. The proposed cut-off values should be considered preliminary and require validation in larger multicenter studies involving different populations and ultrasound systems. Nevertheless, this approach may represent a practical tool for screening at-risk patients, guiding additional imaging studies, and identifying the most affected regions.