It can be subdivided into three elements. In each case, there can be progression to the next stage, but most people don't progress there. The stages are:
- Steatosis (fatty liver) - simple fat accumulation within the hepatocytes (note, not the adipocytes). It is generally believed to be a harmless condition.
- Non-alcoholic steatohepatitis (NASH) - fatty accumulation as above plus associated surrounding inflammation and hepatocyte necrosis. Eventually, this process can progress to include fibrosis, which leads smoothly towards...
- Cirrhosis - obviously not limited to the NAFLD spectrum (it can be caused, and far more commonly is, by other things), but a definite potential outcome of long-standing NASH.
Although some authorities prefer to limit the definition of NAFLD to that caused by insulin resistance, most centres recognise insulin resistance as only the most common cause of NAFLD. The list of other causes is extensive, and includes drugs, toxins, malnutrition, total parenteral malnutrition, dyslipidaemias, etc.
Diagnosis is primarily one of exclusion, but is suggested by:
- unexplained raised transaminases (AST, ALT) - things like viral hepatitis must be excluded
- in associated with an enlarged fatty liver - this can be presumptively shown on ultrasound (hyperechoic/bright liver), CT or even MRI. Only a liver biopsy is definitive, but this is usually not necessary.
- if a significant alcohol history can be excluded
Treatment is again controversial, and much more research is required before any sort of consensus can be reached. Currently, if the cause is insulin resistance, many authorities recommend treating the 'metabolic syndrome' aspects of the condition; specifically, weight loss, and (diabetic) drugs that reduce insulin resistance (metformin and the thiazolidinediones) are promising.