Renal shear wave elastography and intrarenal resistive index in patients on long-term lithium therapy with preserved glomerular filtration

This is the authors' abstract. We don't add key points for this paper.

Lithium remains the gold standard mood stabiliser for bipolar disorder, yet its nephrotoxic potential particularly its capacity to induce chronic tubulointerstitial nephropathy is a source of persistent clinical concern. Standard monitoring relies on serial serum creatinine and estimated glomerular filtration rate (eGFR), but these markers are insensitive to early parenchymal fibrosis and may remain normal until substantial structural damage has already occurred. Renal shear wave elastography (SWE) and the intrarenal resistive index (RI) offer non-invasive, quantitative measures of parenchymal stiffness and vascular resistance that may detect subclinical renal changes at an earlier stage. This cross-sectional research examined 58 adults on continuous lithium therapy for at least two years with preserved renal function (eGFR ?60 mL/min/1.73 m²) and 62 age- and sex-matched controls without lithium exposure, recruited from the Irbid Academy of Diagnostic Medicine, Irbid, Jordan, between September 2022 and November 2024. Bilateral renal SWE (cortical and medullary) and Doppler-derived RI were measured using standardised protocols. Lithium-treated participants demonstrated lower cortical SWE values (7.83 ± 2.14 vs 10.62 ± 1.87 kPa, P<0.001) and higher RI values (0.68 ± 0.06 vs 0.61 ± 0.05, P<0.001) than controls, despite comparable eGFR (mean 81.4 vs 84.7 mL/min/1.73 m², p=0.193). Cortical SWE correlated negatively with lithium duration (r = -0.47, P<0.001) and positively with eGFR (r = 0.34, p=0.009). These findings indicate that SWE and RI can identify subclinical renal parenchymal changes in long-term lithium users whose conventional renal function tests remain within normal limits, supporting their potential as early surveillance tools in this population.