Resistivity Index (RI): A Fast and Reliable Indicator of Lupus Nephritis Severity

Abstract Background: Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by production of pathogenic autoantibodies against nuclear structures. Lupus nephritis (LN) affects up to 60% of patients with SLE who develop immune complex-mediated renal injury and its squeal. Color Coded Doppler Ultrasound (CCDUS) allows non-invasive method for investigating renal hemodynamics. Renal resistive index (RI) measured using CCDUS reflects intrarenal vascular resistance. RI is an essential parameter in renal Doppler US and integrates arterial compliance, pulsatility and peripheral resistance. Aim of Study: Evaluate the role of Color-Coded Doppler Ultrasound in the assessment of nephritis in SLE patients and correlation between resistivity index (RI) and lupus nephritis pathological classes. Such assessment will help reaching diagnosis, guide the choice of management and monitor the follow-up. Patients and Methods: This study was conducted on ninety six SLE patients with renal affection, diagnosed clinically and laboratory first, then each patient included in the study was subjected to Ultrasound Doppler renal examination and renal biopsy. Twenty subjects with normal renal laboratory, ultrasound and Doppler findings were recruited as a control group. B-Mode ultrasound and Color-coded Doppler exami-nation were performed using GE Logiq p5 Ultrasound machine by (3.5-5MHz) transducer. Doppler parameters were adjusted before Doppler examination scan. First general renal vascu-larity was checked then RI was calculated in different segments of intra renal arteries at upper, mild and lower poles. RI=(peak systolic velocity-end diastolic velocity)/peak systolic velocity. The normal value is »  0.60 with 0.70 being around the upper limits of normal. Finally, radiological findings were correlated with clinical findings and correlated with biopsy results. Results: The study included 96 SLE patients, their ages ranged from (13-45) mean 28.19±8.026. Males represented 12.5% (12 patients) and females represented 87.5% (84 patients). Renal biopsy showed 70 patients (73%) with LN and 26 patients (27%) with no renal affection.
The parenchymal echogenicity was increased in all LN seventy patients except one (1.5%). 15 patients (21.5%) scored grade I echogenicity while 16 patients (22.9%) scored grade II and 38 patients (54.1%) scored grade III. There was a significant increase in renal RI in lupus nephritis LN patients, p-value 0.022. Distribution of renal pathologic classes within the LN group. Class II (7 patients) represented 10%, class III (27 patients) represented 38.5%, class IV (22 patients) represented 31,5% and class, V (11 patients) represented 15.7% and class IV (3 patients) repre-sented 4.3 % of LN patients according to biopsy results. There was positive correlation between RI and renal biopsy classi-fication with high significance, p-value 0.001 with r=0.794. Conclusion: There is a significant correlation between pathologic RI and lupus nephritis histological classes suggest-ing a role for RI as a severity marker.