Systematic review with meta-analysis: the significance of histological disease severity in lean patients with nonalcoholic fatty liver disease.

BACKGROUND: Current evidence suggests that lean and obese patients with nonalcoholic fatty liver disease (NAFLD) share an altered metabolic and cardiovascular profile. However, there is an incomplete understanding of the natural history of "lean-NAFLD." Indeed, an unanswered question is whether lean (BMI ≤ 25 Kg/m2 ) NAFLD-patients are protected from severe histological outcomes.

AIM: To perform a meta-analysis with the goal of providing a quantitative estimation of the magnitude of fibrosis, as well as histological features associated with the disease severity, in lean versus overweight/obese-NAFLD patients.

METHODS: Through a systematic search up to July 2017, we identified eight studies that compared histological outcomes in lean (n = 493) versus overweight/obese (n = 2209) patients.

RESULTS: Relative to lean-NAFLD, overweight/obese-NAFLD patients showed significantly (P = .032) higher fibrosis scores; the observed difference in means between the two groups, which is the absolute difference between the mean value of fibrosis score [0-4] ± standard error, was 0.28 ± 0.13. The risk of having nonalcoholic steatohepatitis-NASH (OR 0.58 95% CI 0.34-0.97) was significantly lower in lean-NAFLD (n = 322) than in overweight/obese-NAFLD (n = 1357), P = .04. Relative to lean-NAFLD, overweight/obese-NAFLD patients also have significantly greater NAFLD activity (difference in means ± SE: 0.58 ± 0.16, P = .0004) and steatosis (difference in means ± SE: 0.23 ± 0.07, P = .002) scores.

CONCLUSIONS: Lean-NAFLD patients tend to show less severe histological features as compared to overweight/obese-NAFLD patients. Subsequent longitudinal assessment is needed to understand the clinical impact of these findings; however, the significant ~ 25% increment of mean fibrosis score in overweight/obese patients suggests that obesity could predict a worse long-term prognosis.