Special articleHepatic histology in obese patients undergoing bariatric surgery
Introduction
Non-alcoholic fatty liver disease (NAFLD) is a spectrum of liver disease that encompasses steatosis alone to non-alcoholic steatohepatitis (NASH) and can progress to cirrhosis and liver failure. NAFLD is one of the most important forms of liver disease in the developed countries, occurring in 20% to 25% of the general population [1], whereas NASH occurs in about 3% [2], [3].
Obesity and insulin resistance (IR) are believed to exert the main pathophysiological role in the development of NAFLD [4], [5], [6], [7], [8]. The prevalence of obesity has increased tremendously in the last half century [9]. A further increase in the prevalence of NAFLD is expected in the future. However, until recently, few data were available on the prevalence of NAFLD and NASH in severely obese patients, defined as a body mass index (BMI) higher than 35 kg/m2. Further, the risk factors for a more aggressive liver disease in this population have yet to be clearly defined.
In the last 5 years, investigators have been trying to identify the real prevalence of NAFLD and NASH in the population of severely obese patients admitted to bariatric surgery, with systematic liver biopsy at the time of surgery. Although most studies had a very similar design, still their results were quite dissimilar. Thus, we conducted an in-depth review of available studies on the prevalence and risk factors for NAFLD in morbidly obese subjects, in order to summarize and evaluate the published data and to discuss discrepant findings.
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Materials and methods
We conducted a literature search using MEDLINE and Current Contents to identify relevant articles published in any language, until December 2005. We also manually searched the references of retrieved articles to identify additional relevant published studies. Search criteria included MEDLINE medical subject heading terms for NAFLD, NASH, morbidly obesity and bariatric surgery. Studies were eligible if they reported prevalence data regarding systematic liver biopsy in morbidly obese patients
Results
Seventeen studies were selected [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], of which five [10], [17], [20], [21], [26] were excluded because of their retrospective design or other methodological issues. The remaining twelve publications were transversal, observational studies with a prospective and consecutive recruitment of patients, enrolling a total of 1620 severely obese patients. Their main characteristics are summarized in Table 1.
Discussion
The present review found an enormous discrepancy in the prevalence of NASH in individuals with severe obesity. This is unexpected, given the fact that study design and patients demographics were quite similar in all studies. The first logical explanation would be a difference in geographic location with associated ethnic or dietary/life style differences. In fact, if we consider studies from the USA alone, there is a more uniform prevalence of NASH, with a relatively lower prevalence. On the
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