NAFLD and autoimmune hepatitis: Do not judge a book by its cover.

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease (almost 25% of the general population). Autoimmune hepatitis (AIH) is a relatively rare liver disease of unknown aetiology characterized by female predominance and large heterogeneity regarding epidemiology, clinical manifestations, genetics, serology and liver pathology. The potential NAFLD/AIH coincidence or an AIH diagnosis alone instead of NAFLD represent a challenge for clinicians, both in making a correct and timely diagnosis but also in the management of these diseases. The diagnosis of both diseases can be challenging as: (a) reliable laboratory tests to confidently diagnose or exclude NAFLD or AIH are missing; (b) physicians and pathologists are much more familiar with a very common disease like NAFLD so, they do not consider an alternative or additional diagnosis; (c) most NAFLD studies do not investigate the patients for all autoantibodies involved in AIH diagnosis, apply the diagnostic scoring systems for AIH or address the possibility of AIH features on liver histology and (d) the recent European and American practice guidelines for NAFLD do not mention clearly the importance of IgG determination and liver autoimmune serology according to the AIH guidelines. Patients with NAFLD/AIH coincidence have significantly more frequently hypertension, diabetes, obesity, older age, lower transaminases, bilirubin and simplified score for AIH diagnosis but no female predominance compared to AIH patients only. The true outcome of NAFLD/AIH patients is practically unknown while their management is quite problematic because official clinical practice guidelines for this condition are missing.