Abstract
Background: Obesity is a primary limiting factor in liver stiffness measurement (LSM). The impact of obesity has always been evaluated in terms of body mass index (BMI), without studying the effects of skin-to-liver distance (SLD) on LSM. We studied the impact of SLD on LSM in a cohort of obese patients undergoing bariatric surgery and intra-operatory liver biopsy. Materials and Methods: 299 patients underwent LSM by point-shear wave elastography (ElastPQ protocol), with two different ultrasound machines. SLD was measured as the distance between the skin and the liver capsule, perpendicular to where the region of interest (ROI) was positioned. We used the following arbitrary cut-offs: <5.7 kPa, F0–1; 5.7–7.99 kPa, F2; ≥8 kPa, F3–4. Results: We developed two logistic regression models using elastography–histology agreement (EHA) as the dependent variable and SLD as the independent variable. The model based on the second machine showed strongly more performant discriminative and calibration metrics (AIC 38.5, BIC 44.2, Nagelkerke Pseudo-R2 0.894, AUROC 0.90). The SLD cut-off value of 34.5 mm allowed a correct EHA with a sensitivity of 100%, a specificity of 93%, negative predictive value of 100%, positive predictive value of 87%, an accuracy of 96%, and positive likelihood ratio of 3.56. Conclusion: The impact of SLD is machine-dependent and should be taken into consideration when interpreting LSM. We believe that our findings may serve as a reference point for appropriate fibrosis stratification by liver elastography in obese patients.
Highlights
Obesity is a global epidemic, with an estimated number of 650 million obese adult individuals worldwide [1]
The main aim of liver elastography introduction in the daily clinical practice is to replace the need of liver biopsy, which despite its invasive nature [32], sampling errors [33], and intra/inter-observer variability [34], remains the gold standard in hepatic fibrosis staging [35]
Liver elastography could be proposed as a non-invasive tool to stage fibrosis in high-risk patients who would not have indications for liver biopsy, such as obese patients
Summary
Obesity is a global epidemic, with an estimated number of 650 million obese adult individuals worldwide [1]. The success rate is technique-dependent: a recent meta-analysis demonstrated that TE has a higher failure rate in obese patients if compared to point-Shear Wave Elastography (pSWE) (11.3% vs 0.8%) [11]. Despite the higher success rate of pSWE, few studies have addressed the lack of cut-off values to discriminate between liver fibrosis stages [12]. LSM could optimally discriminate between fibrosis stages for SLD
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