The Renal Resistive Index in systemic sclerosis: Determinants, prognostic implication and proposal for specific age-adjusted cut-offs

Background: Renal Resistive Index (RRI), reflects changes in both renal vascular and tubular-interstitial compartments and in systemic vascular compliance related to age and comorbidities. Objectives: a) To investigate determinants of RRI in SSc population, b) its association with SSc-related features and c) to test its prognostic impact on organ specific worsening or death. Methods: 380 SSc patients ≥18 years were enrolled after giving informed consent. Baseline data on RRI, laboratory, instrumental and therapeutic features were retrospectively collected. Age-SSc adjusted cut-offs were created by dividing the population in age quartiles and considering RRI values >75th percentile as pathologic. Clinical follow-up was performed until last available visit or the development/worsening of specific internal organ involvement or death. Results: RRI was independently predicted by age and systolic pulmonary arterial pressure on Echo. Therefore, we created Age-SSc adjusted pathologic RRI cut-offs, which were significantly associated with various disease related skin and lung fibrotic manifestations, as well as vasculopathic complications. After a mean follow-up of 3.6 ± 2.6 years, RRI was one of the independent predictors (together with modified Rodnan skin score, interstitial lung disease, presence of dyspnoea and late nailfold-videocapillaroscopy pattern) for mortality, with 0.68 as best cut-off (sensitivity 88.5%, specificity 50.9%). Conclusion: If corroborated, Renal Resistive Index cut-offs might be used to evaluate renal and extrarenal involvement in SSc and could serve as predictors of mortality.