Hepatic steatosis is defined as the accumulation of fat (mainly triglycerides) in the cytoplasm of liver cells1. Echosens gives you more details about this disease, and the interest to quantify it.

 

Liver stiffness Echosens

 


This overload results from an imbalance between the production of triglycerides by the hepatocytes (due to the mobilization of the fatty acids of the fatty tissue of food origin or the reduction of their oxidation inside the mitochondria) and their evacuation through blood, in the form of lipoproteins.

 


Hepatic steatosis (nonalcoholic) covers a whole spectrum of different forms and gravity:
- Non-progressive steatosis (nonalcoholic)
- Steatohepatitis (nonalcoholic) progressive, accompanied by an inflammatory state and which can evolve towards fibrosis and cirrhosis.

It is therefore necessary for the physician to recognize patients with a progressive form in order to offer them regular control and possible therapeutic management2.

 

Until now, no non-invasive examination can be used to diagnose any of these two conditions, nor ultrasound or radiology. Histology is still considered as the reference for the diagnosis of steatosis3. But hepatic biopsy is an invasive procedure, difficult to propose routinely in order to diagnose a pathology that will remain mostly indolent4.

 

Histological examination does not allow precise quantification of steatosis. According to the methods used, this tool measures, in three to five classes, the proportion of hepatocytes containing steatosis vacuoles.
Quantification is very rough and reflects only the proportion of hepatocytes affected, without any data on the actual amount of liver triglycerides4.

 

Moreover, this examination is incapable of distinguishing the histological image of NASH from that of alcoholic steatohepatitis or alcoholic steatohepatitis, and it is only by interrogating the patient that alcohol abuse can be excluded2.

 

Ultrasound and CT scan can be used to diagnose a steatosis of greater than 30% in histological grade, but finer quantification is impossible. Magnetic resonance imaging (MRI) is a powerful tool for quantifying steatosis, but its use seems to be reserved for clinical research studies and therapeutic trials rather than routine and daily use. In France, MRI is still rather difficult to access, with a cost that does not allow it to be considered as a tool for quantifying steatosis on a large scale4. None of these imaging examinations (ultrasound, CT scan and MRI) can detect the degree of inflammation or fibrosis1.

 

Interview with Professor Victor de Ledinghen, Head of the Department of Hepato-Gastroenterology and Digestive Oncology at the Haut-Levêque Hospital CHU of Bordeaux Pessac

Why bother quantifying fatty liver disease?

 

Fatty liver disease is a condition caused by the presence of excessive fat in the liver. In itself, it is not dangerous. However, patients with fatty liver disease run the risk of subsequently developing inflammatory damage which may in turn cause fibrosis, cirrhosis and cancer. This is known as metabolic steatopathy and is mainly seen in diabetic and obese patients. It is the first stage of a disease that may later become serious.

 In medicine, the earlier a disease is diagnosed, the better it can be treated. If we can measure the steatosis, we will be able to diagnose a potentially life-threatening condition at a very early stage.

 Fatty liver disease is also an aggravating factor in hepatitis C and a risk factor for complications in patients undergoing a liver transplant. Once the diagnosis has been reached and treatment started, measuring steatosis can also be a means of assessing treatment efficacy. If there is less fatty liver, then the treatment can be considered to be effective. If this is not the case, then the treatment will have to be modified.

 

Can you describe a FibroScan® examination?

 

The Fibroscan® provides a totally non-invasive, user-friendly and painless means of measuring hepatic fibrosis.

The Fibroscan uses Vibration Controlled Transient Elastography (VCTETM) at 50 Hz to measure liver stiffness. A new method, Controlled Attenuation Parameter (CAPTM), has been coupled with the Fibroscan® making it possible to measure – and above all quantify - hepatic steatosis for the very first time. Both parameters are measured simultaneously; without prolonging the examination time.

New software allows calculation of the extent of steatosis (by measuring attenuation of the ultrasound signal) at the same time as fibrosis (measuring the speed with which a shock wave crosses the liver tissue), using either the M or the XL probe placed on the skin, over the liver and perpendicular to the skin. The procedure can be done either by a trained physician or by trained nursing staff.

As is the case for other imaging techniques, the results are interpreted by a doctor.

 

What are the advantages over liver biopsy?

 

A biopsy is not to be taken lightly. It is an invasive examination that brings with it a high risk of complications, the main one being haemorrhaging which can be fatal.

A biopsy cannot be repeated regularly, every three to six months for instance. It can’t even be done on an annual basis, and this makes it difficult to monitor treatment efficacy. In addition, a liver biopsy only evaluates about 1/50 thousandth of the liver, whilst the Fibroscan® probe evaluates 1/500th of the liver, i.e. 100 times more liver tissue.

In theory, the non-invasive Fibroscan® examination is therefore 100 times more representative than a liver biopsy. More reliable and risk-free, the examination can be repeated as often as needed.

 

How is it currently being used and are the examinations reimbursed by the national insurance system in France?

 

At the present time, the Caisse Nationale d’Assurance Maladie (CNAM) [France’s national health insurance body] only reimburses Fibroscan® examinations for patients with hepatitis C.

If the examination is done for reasons unrelated to hepatitis C, it is therefore not reimbursed. It is important to continue to develop its uses in other indications, such as diabetes, hypertension and obesity, so that the CNAM can reimburse examinations performed in these other patient groups.

The examination costs almost 30 times less than a liver biopsy. Each of the geographical departments in France has at least one traditional Fibroscan; some centers also have the equipment required to measure both fibrosis and steatosis. In the future, its use could be extended to other diseases, such as alcohol dependency which is the leading cause of liver damage in France.

 As steatosis decreases with abstinence, this examination could be a valuable means of monitoring patients and their willingness to stop drinking.

 

What do you feel is most important about CAP and its development?

 

It is important to point out that, before CAP was launched, the only way to diagnose steatosis was through conventional ultrasound.

Quantification was not possible at all. A liver ultrasound will show that steatosis is present only if it represents more than 30% of the liver tissue. CAP is currently the only non-invasive examination that genuinely quantifies steatosis.

It is much more precise, which is very important in terms of diagnosis and prognosis for patients.

 

Bibliography :

 

 

  1. Van Hool M. Stéatose hépatique et NASH. Le Journal du Médecin. 2005:356-360
  2. Oneta CM, Dufour JF. Diagnostic, pronostic et possibilités thérapeutiques de la stéatose hépatique non alcoolique. Forum Med Suisse. 2003;37:862-8.
  3. Horsmans Y. La stéatose hépatique non alcoolique. Louvain Med. 2000;119:S23-S25.
  4. Aubé C. Quantifier la stéatose hépatique, pourquoi ? comment ? J Radiol. 2009;90:1675.