Metabolic Dysfunction-Associated Steatohepatitis With Positive Antimitochondrial M2 Antibodies: Diagnostic Pitfall and Importance of Follow-Up.

Metabolic dysfunction-associated steatohepatitis (MASH) is a subtype of metabolic dysfunction-associated steatotic liver disease (MASLD) characterized by liver fat accumulation and inflammation. Occasionally, patients with MASH may test positive for antimitochondrial M2 antibodies (AMA-M2), which are usually linked to primary biliary cholangitis (PBC), creating potential diagnostic confusion. We report the case of a 52-year-old woman with obesity and persistent liver enzyme elevation, who was found to have positive AMA-M2 antibodies. Imaging revealed moderate hepatic steatosis, and liver biopsy confirmed MASH without evidence of PBC. After adopting lifestyle modifications, the patient achieved significant weight loss and normalization of liver and lipid profiles. At the one-year follow-up, the patient showed isolated elevation of alkaline phosphatase, which, together with positive anti-M2 antibodies, led to a diagnosis of PBC and initiation of ursodeoxycholic acid therapy. This case illustrates that anti-M2 antibodies may be found in patients with MASH alone or in those with MASH associated with PBC, highlighting the importance of careful evaluation and long-term follow-up.