Evaluation of Renal Stiffness Using Shear Wave Elastography in Patients with Inactive Lupus Nephritis

<b>Background/Objectives:</b> Lupus Nephritis (LN) is a major complication of Systemic Lupus Erythematosus (SLE) leading to significant morbidity. While biopsy is the gold standard, non-invasive tools are needed for longitudinal monitoring. This study aims to evaluate the diagnostic utility of Shear Wave Elastography (SWE) in detecting subclinical renal damage (fibrosis) in SLE patients with a history of LN who are currently in clinical remission (inactive disease), and to compare its efficacy with Doppler ultrasonography (DUS). <b>Methods:</b> This cross-sectional study included 80 SLE patients and 41 age- and sex-matched healthy controls. Crucially, all SLE patients were in the clinically inactive disease (SLEDAI-2K < 6) at the time of evaluation. Patients were stratified into two groups: those with a history of LN (LN Group, n = 37) and those without (Non-LN SLE Group, n = 43). Strict exclusion criteria were applied to eliminate non-SLE renal comorbidities. Renal parenchymal stiffness (kPa) was measured using SWE, and the renal resistive index (RI) was assessed using DUS. SWE findings were correlated with renal function tests and disease activity scores. <b>Results:</b> Despite being in clinical remission, the LN group exhibited significantly higher renal stiffness values (Median: 1.60 kPa) compared to the non-LN SLE group (1.40 kPa, <i>p</i> < 0.001) and healthy controls (1.32 kPa, <i>p</i> < 0.001). No significant difference was observed between the non-LN SLE group and controls. Unlike SWE, renal RI values showed no statistically significant difference among the groups (<i>p</i> > 0.05). Correlation analysis revealed that renal stiffness was positively associated with prior serum creatinine and disease activity (SLEDAI-2K), and negatively associated with eGFR. <b>Conclusions:</b> SWE is superior to DUS (RI) in detecting renal parenchymal changes in LN patients. The persistence of elevated stiffness during the inactive disease suggests that SWE captures cumulative chronic damage (remodeling and fibrosis) rather than just acute inflammation. Consequently, SWE holds promise as a non-invasive surrogate for monitoring disease chronicity in SLE patients.