Nonalcoholic steatosis (NASH)
NASH is a very common condition in New Zealand and is seen particularly in overweight, diabetic patients with elevated cholesterol.
What is NASH?
The accumulation of fat within the liver is called fatty liver (steatosis). Excess alcohol intake, as well as producing fatty liver (steatosis) may also produces inflammation of the liver (hepatitis), when these occur together it is called steatohepatitis. It has been recognised that the combination of fatty liver and liver inflammation has many causes other than excess alcohol intake.
The name nonalcoholic steatohepatitis (NASH) refers to those conditions that resemble alcohol induced liver damage, but that are not due to alcohol intake, common causes include obesity, diabetes and certain drugs.
Why does NASH matter?
NASH is important because it may lead to scarring of the liver (cirrhosis) and of this Fatty liver in itself probably does not lead to progressive liver damage and cirrhosis. It appears that it is the presence of inflammation in NASH that is results in progressive damage to the liver and eventually cirrhosis. For NASH to progress to cirrhosis probably takes many years or decades. Progression of NASH to cirrhosis is not inevitable: if the underlying condition that caused NASH is effectively treated liver inflammation and excess fat will recede and the liver return to normal.
What causes NASH?
In one sense the accumulation of fat within the liver is not a disease but is a reflection of the highly efficient way in which your body can store energy. Fat is the most concentrated form of energy available; it provides double the calories by weight than both carbohydrate and protein when metabolised. The ability of your liver to store fat, therefore, represents a survival advantage during a period of starvation.
On the other hand, at some point the excessive storage of fat within the liver is associated with inflammation and then progressive liver damage. It is not known why some people develop this inflammation and others do not.
How is NASH diagnosed?
In the majority of patients NASH does not produce any symptoms. Physical examination is usually normal, but occasionally, the liver is enlarged and tender. The diagnosis is often first suspected after finding abnormal blood tests of liver function taken for unrelated issues. The usual laboratory features include a mild elevation of liver enzymes. There are a range of liver diseases that can produce similar changes in the liver enzymes so blood tests are taken to exclude these alternate diagnoses. Ultrasound and CT scans of the liver have characteristic features to help make the diagnosis. The definitive test is to look at a tissue sample (biopsy) of the liver under the microscope.
What is the treatment for NASH?
NASH is not a disease entity in itself but the response of the liver to the conditions under which it is being asked to work. Therefore, if the cause of your NASH is being overweight then weight loss is the treatment. Likewise if your diabetes is poorly controlled then improved glucose control is the treatment. Dietary and drug treatment of elevated cholesterol and triglyceride levels also may help if this is the cause of your NASH.
In addition, a graded exercise programme is recommended to improve physical fitness and the energy (fat) demands of your body. Finally, of course, your alcohol intake should be kept to the minimum recommended limits.
Your best defence against fatty liver is to maintain a healthy weight and normal cholesterol and blood sugar levels. This strategy, along with avoiding excess alcohol and other substances that could be harmful to your liver, will reduce your risk of liver disease.