The diagnosis of autoimmune hepatitis (AIH) leans on a characteristic biopsy pattern, although none of the individual findings is exclusive to the disease.
Interface hepatitis
The histological pattern required for the diagnosis is interface hepatitis, inflammation at the portal-parenchymal interface (PPI) — the region between the portal triad and the lobule of the liver, where the connective tissue of the portal tract meets the hepatocytes. Interface hepatitis is necessary for the diagnosis but is not specific to AIH; other forms of chronic hepatitis can produce it as well.
Alongside it, the typical picture includes two other features:
- hepatocyte rosettes, clusters of hepatocytes arranged around a small lumen and embedded in connective tissue
- lymphocyte emperipolesis, a lymphocyte lying within the cytoplasm of a hepatocyte rather than between the cells
Other biopsy features
Plasma cells can be abundant at the interface or throughout the acinus. When plasma cells are present together with moderate-to-severe interface hepatitis, the combination has a specificity of 81% and a positive predictive value of 68% for AIH.
Centrilobular necrosis of zone 3, the zone around the central vein, is seen in about 29% of AIH patients and is a feature of acute presentations. Bridging necrosis and multi-acinar necrosis indicate a severe inflammatory reaction. Pan-acinar hepatitis can be found during an acute severe relapse after withdrawal of treatment.