Multifaceted pathogenesis of liver steatosis in inflammatory bowel disease: a systematic review.

Non-Alcoholic Fatty Liver Disease (NAFLD), as a hepatic manifestation of metabolic syndrome (MET)-related obesity, insulin resistance, dyslipidemia, and hypertension, is the main cause of chronic liver disease. Inflammatory Bowel Diseases (IBD), (Crohn's Disease (CD) and Ulcerative Colitis (UC)), are often associated with extraintestinal manifestations. Of these, NAFLD is one of the most frequently reported. To highlight the etiopathogenesis of NAFLD in IBD, we performed a systematic review emphasizing the relationship between NAFLD genetic alterations, metabolic syndrome, and drugs. According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses Statement (PRISMA) criteria, we performed a systematic literature search on PubMed, Google Scholar, and Web of Science for literature updated from 2010 to 1 March 2021. Inclusion criteria for studies were observational design and Randomized Controlled Trials (RCTs); written in English; primary research only; based on adult patients, and human research only. We identified nine studies on the link between NAFLD and IBD. Among these, two described the genetic predisposition to NAFLD of patients with IBD. Four reported an association between MetS and NAFLD in IBD patients. Regarding medications, none of four studies included, detected a relationship between NAFLD onset and IBD treatment (corticosteroids, immunomodulators, methotrexate, or biologics).  However, a retrospective study showed a protective effect of anti-TNF alpha therapies against altered liver enzymes. In this interplay between genetic, metabolic, drug, and inflammatory factors, the underlying pathogenic mechanisms behind NAFLD in IBD are still far from clear. Further studies are needed to better clarify the role of individual components influencing the development of NAFLD in IBD.