Microvascular ultrasonography for quantitative evaluation of nailfold vasculature in systemic sclerosis

Systemic sclerosis (SSc) is characterized by microvascular dysfunction affecting the digital vasculature. Microvascular ultrasonography (MVUS) is a technique capable of detecting low-velocity flow. This study aimed to evaluate nailfold microvasculature in SSc using the MVUS-derived color pixel percentage (CPP) quantitatively. Seventy-two participants were included in this cross-sectional observational study. Thirty-seven participants had SSc, 19 participants were healthy controls, and 16 individuals were hypertensive, receiving calcium-channel blockers (CaCBs). Nailfold ultrasonography was performed on all ten digits using a 24-MHz linear transducer and MVUS (ultramicro-angiography®, Mindray Resona R9). CPP was defined as the proportion of colored pixels representing detectable microvascular flow within a predefined, standardized nailfold region of interest, using uniform image acquisition and analysis criteria. Inter-observer reliability was assessed using intraclass correlation coefficients (ICCs). Group differences were examined with one-way ANOVA. CPP measurements demonstrated excellent reproducibility (ICC 0.986–0.996). CPP values were symmetric across digits of both hands in SSc patients and healthy controls. Across all ten digits, CPP values were significantly lower in SSc patients than in healthy controls and CaCB-treated hypertensive individuals (all p < 0.001). CPP values were consistently highest in the HT with CaCBs group. MVUS provides a sensitive and reproducible method for quantifying nailfold microvascular flow. The markedly reduced CPP values observed in SSc patients reflect diffuse microvascular impairment associated with the disease. These findings support further investigation of CPP as a quantitative marker of vascular involvement and as a potential tool for future longitudinal evaluation in systemic sclerosis, which may complement existing clinical and morphological assessments of microvascular disease.