The Renal Resistive Index: A New Biomarker for the Follow-up of Vascular Modifications in Systemic Sclerosis

Objective. The aim of the present retrospective observational study was to evaluate the change of Renal Resistive Index (RRI) over time (Delta RRI) and under treatment in patients with systemic sclerosis (SSc) as well as to correlate these changes with disease complications.Methods. Two hundred thirty patients [29 male, median age 57 (IQR 48-67) yrs] were enrolled. At baseline and follow-up (3.43, IQR 2.81-4.45 yrs), we collected the following data: disease variables, nailfold video-capillaroscopy (NVC) pattern, forced vital capacity (FVC), diffusing lung capacity for carbon monoxide (DLCO), systolic pulmonary arterial pressure (sPAP), presence of interstitial lung disease, RRI, evaluation of glomerular filtration rate, and new onset of pulmonary arterial hypertension (PAH).Results. RRI value is high in SSc patients with digital ulcers and anticentromere antibodies, active and late NVC patterns, and limited cutaneous SSc. A significant correlation was observed between ARRI and Delta sPAP (R = 0.17, P = 0.02), with statistically higher ARRI (0.08 +/- 0.02 vs 0.03 +/- 0.05, P = 0.04) in patients complicated by PAH onset. No other new-onset complication was associated with Delta RRI. The receiver-operating characteristic curve analysis confirmed the predictive role of Delta RRI in development of new PAH (area under the curve 0.84, 95% CI 0.75-0.93, P = 0.02). In patients with SSc never exposed to sildenafil, ARRI was higher (0.04 +/- 0.05) compared to both patients exposed to sildenafil during the study period (0.01 +/- 0.05, P = 0.03) or in those exposed at the time of baseline evaluation (0.00 +/- 0.05, P = 0.01).Conclusion. RRI and its variation in time are a reliable marker of SSc-related vasculopathy, both in renal and extrarenal compartments.