Nonalcoholic fatty liver disease (NAFLD) is the most common cause of elevated serum aminotransferase levels in the United States. It has been estimated that approximately 80 million Americans have NAFLD, and the prevalence of this condition is expected to rise with a continuing epidemic of obesity. Nonalcoholic steatohepatitis (NASH), which is the progressive form of NAFLD, is typically associated with inflammation and cellular injury in addition to steatosis, with or without perisinusoidal fibrosis and liver histology. Liver biopsy is the gold standard for diagnosing NAFLD as well as confirming the presence of NASH. However, liver biopsy is an invasive procedure and therefore is not routinely favored by physicians and patients because of potential risk. Thus it is not practical to subject all patients to use liver biopsy for this assessment. As a result, noninvasive biomarkers are needed.
Recently, Noureddin and colleagues (2013) have described an innovative application of an emerging MRI-based biomarker named protein density fat-fraction (PDFF) for quantification of hepatic liver fat in patients with NASH. In their study, 50 patients with biopsy-proven NASH were enrolled in a randomized, double-blind, placebo-controlled trial. They were randomized to receive placebo or the agent colesevelam, a drug known to reduce elevated low-density lipoprotein (LDL) cholesterol and to improve glycemic control in adults with type II diabetes. The authors performed cross-sectional comparisons of MRI-derived PDFF together with MR spectroscopy (MRS)-derived PDFF and nontargeted liver biopsy, at baseline and after 24 weeks of treatment.
This study demonstrated excellent agreement and correlation between MRI and MRS and also demonstrated excellent correlation with both MRI and MRS and histology-derived steatosis grade. Especially noteworthy is the fact that the authors determined that longitudinal changes in MRI-derived PDFF was more sensitive to the detection of changes in liver fat than biopsy, with changes in liver fat paralleling changes in body weight and serum aminotransferases between baseline and week 24.
These exciting results demonstrate the utility of quantitative MRI methods for treatment monitoring using a novel, noninvasive image-based biomarker of hepatic steatosis. In commenting on this work, Dr. Scott Reeder (2013) suggested "the imminent widespread clinical availability of MRI methods to measure PDFF in the clinical setting will undoubtedly play an important role in the study and clinical management of patients with diffuse liver disease."
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