What should we know about transient hepatic elastography and its application in Non-alcoholic fatty liver disease?

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Non-alcoholic steatohepatitis (NASH) corresponds to the group of patients with non-alcoholic fatty liver disease (NAFLD) who present, in addition to predominantly macrovesicular steatosis, with hepatocyte ballooning, lobular inflammation, liver fibrosis, cirrhosis and risk of progression to hepatocellular carcinoma (HCC). Learn more in this other article.

About 30-40% of adults have NAFLD and of these, 3-12% evolve with NASH, with prevalence in progression in recent years, especially due to the strong association with metabolic factors such as obesity. Thus, NASH has become in recent years the main cause of liver transplantation in the world

In the evaluation of patients with NAFLD, it is essential to assess which non-invasive tests (NIT) can contribute to the investigation. Although abdominal ultrasound is the first-line examination in the initial evaluation of patients with NAFLD, it is operator-dependent and has low sensitivity for mild hepatic steatosis: typically, steatosis needs to affect more than 30% of hepatocytes to be detectable by this method.

Among the NITs available in our environment, transient hepatic elastography (FibroScan®, Echosens, Paris, France; TE) is the most commonly used by hepatologists. The technology was approved in 2013 by the Food and Drug Administration in the United States and quickly incorporated in the evaluation of patients with hepatopathy of different etiologies, including those with NAFLD.

Advantages of the method

Through the appropriate selection of one of the probes (Small, Medium and XL) by age, physical type and skin-liver distance, the examination is performed non-invasively and quickly, allowing the quantification of liver fat by CAP (controlled attenuation parameter) and liver fibrosis by assessing liver stiffness (liver stiffness measurement; LSM).

The reference point is guided by anatomical markers (meeting of the mid-axillary line with transverse and parallel line to the costal margins, at the level of the xiphoid appendix).

LSM

Through vibrations of low amplitude and low frequency (50Hz) emitted by the probe at the reference point, a shear wave propagates through the liver tissue at a certain speed (m/s): the stiffer the tissue, the faster the propagation of the wave. The LSM ranges from 1.5 to 75 kilopascals (kPa) and assesses liver stiffness in a volume 100 times larger than a liver biopsy.

The values of LSM vary according to the etiology of the hepatopathy, with the values of AUROC for F1, F2, F3 and F4 of 0.82, 0.85, 0.94 and 0.96, respectively, being reported in NAFLD. For advanced fibrosis (F3-F4), the cut-offs range from 8-12kPa, with a sensitivity of 84-100% and specificity of 83-97%.

Note 1: Some cross-sectional studies and head-to-head comparison indicated better accuracy of MR elastography in the evaluation of liver fibrosis compared to TE, in the identification of fibrosis (F1-F4) with specificity (F4, 94.5% vs 75.9%), however, the factors cost, availability and examination time (duration) are limiting factors of elastoRM in clinical practice.

CAP

An AUROC of 81-84% ?E1 (steatosis in at least 5-10% of hepatocytes); 85-88% for ?E2 (33%) and 86-91% for E3 (66%), with sensitivity for ?E1, ?E2 and E3 of 60-75%, 69-84% and 77-96%, respectively. The cut-offs for CAP is 248 dB/m for E1, 268 dB/m for E2 and 280 dB/m for E3.

Note 2: Although abdominal resonance with proton density fat fraction (MR-PDFF) has better sensitivity and specificity for the quantification of liver fat fraction compared to CAP, the factors cost and availability are the major limitations in clinical practice.

Reliability criteria

According to the manufacturer’s recommendations, during TE, 10 valid measurements should be obtained, with a success rate >60% and an interquartile range (IQR) ?30%.
Some studies have shown that IQR > 40 dB/m of CAP with M probe was associated with lower reliability for the diagnosis of liver steatosis, but additional studies are needed for validation as a criterion.

Limitations and considerations of the method

One of the biggest challenges of TE is the lower success rate in obese patients. While the M probe is indicated for adults with normal weight (BMI <25kg/m²) and the S probe for children and adolescents, the XL probe is indicated for obese patients or those with skin-liver distance greater than 3.5cm, as this probe allows greater depth in the evaluation of liver stiffness (35-75 vs 25-65mm) and CAP.

Prospective studies indicate that the XL probe estimates higher liver stiffness value than the M probe when applied in the same patient, however, high BMI tends to overestimate the LSM, thus, the effects of obesity and the XL probe tend to cancel each other out.

Other factors that impair LSM are: liver congestion, biliary obstruction, amyloidosis, focal liver lesions, increased transaminases (1-5xLSN) and ascites.

It is essential to instruct the patient to fast for 3-4 hours before the examination, as increased portal flow can increase the LSM by 1-5kPa (peak at 20-40 minutes, with duration of up to 180 minutes, on average).

Clinical application

In addition to the evaluation of liver stiffness and quantification of steatosis, TE has an important role in predicting complications of compensated advanced chronic liver disease (cACLD), such as esophageal varices (EV), HCC and liver-related death.

According to Baveno VII, in general:

1. LSM ?15kPa and platelets ? 150,000 excludes clinically significant portal hypertension (CSPH, sensitivity and negative predictive value >90%) in patient with cACLD;
2. LSM <20kPa and platelets > 150,000 allows to avoid performing EDA screening of EV;
3. In patients of viral, alcoholic and non-obese NASH etiology (BMI <30kgm/²), LSM ? 25 is sufficient to exclude CSPH (sensitivity and positive predictive value >90%).
4. In patients with cACLD due to NASH, the ANTECIPATE model can be used to predict the risk of CSPH, but additional validation is needed.

Guidelines Recommendations

TE is a validated NIT and recommended by the AASLD and EASL guidelines and, according to its availability, should be incorporated as a tool in the evaluation of patients with NAFLD in clinical practice.

References

1. Zhang X, Wong GL, Wong VW. Application of transient elastography in nonalcoholic fatty liver disease. Clin Mol Hepatol. 2020 Apr;26(2):128-141. doi: 10.3350/cmh.2019.0001n. Epub 2019 Nov 8. PMID: 31696690; PMCID: PMC7160347.
2. Younossi ZM, Loomba R, Anstee QM, Rinella ME, Bugianesi E, Marchesini G, Neuschwander-Tetri BA, Serfaty L, Negro F, Caldwell SH, Ratziu V, Corey KE, Friedman SL, Abdelmalek MF, Harrison SA, Sanyal AJ, Lavine JE, Mathurin P, Charlton MR, Goodman ZD, Chalasani NP, Kowdley KV, George J, Lindor K. Diagnostic modalities for nonalcoholic fatty liver disease, nonalcoholic steatohepatitis, and associated fibrosis. Hepatology. 2018 Jul;68(1):349-360. doi: 10.1002/hep.29721. PMID: 29222917; PMCID: PMC6511364.
3. Park CC, Nguyen P, Hernandez C, Bettencourt R, Ramirez K, Fortney L, Hooker J, Sy E, Savides MT, Alquiraish MH, Valasek MA, Rizo E, Richards L, Brenner D, Sirlin CB, Loomba R. Magnetic Resonance Elastography vs Transient Elastography in Detection of Fibrosis and Noninvasive Measurement of Steatosis in Patients With Biopsy-Proven Nonalcoholic Fatty Liver Disease. Gastroenterology. 2017 Feb;152(3):598-607.e2. doi: 10.1053/j.gastro.2016.10.026. Epub 2016 Oct 27. PMID: 27911262; PMCID: PMC5285304.
4. de Franchis R, Bosch J, Garcia-Tsao G, Reiberger T, Ripoll C; Baveno VII Faculty. Baveno VII – Renewing consensus in portal hypertension. J Hepatol. 2022 Apr;76(4):959-974. doi: 10.1016/j.jhep.2021.12.022. Epub 2021 Dec 30. Erratum in: J Hepatol. 2022 Apr 14;: PMID: 35120736.

How to cite this file

Oti KST., What should we know about transient hepatic elastography and its application in non-alcoholic fatty liver disease?. Gastropedia, 2022. Available at: https://gastropedia.com.br/gastroenterologia/figado/o-que-devemos-saber-sobre-a-elastografia-hepatica-transitoria-e-sua-aplicacao-na-doenca-hepatica-gordurosa-nao-alcoolica/