A 30-year-old woman is found to have elevated ALT and AST. Liver biopsy shows periportal hepatocyte rosetting, lymphoplasmacytic infiltrate in portal tracts extending into lobule, and interface hepatitis with emperipolesis. Anti-smooth muscle antibodies are positive at 1:640. What histological finding is most specific for autoimmune hepatitis (AIH) type 1?

• A Copper accumulation in periportal hepatocytes
• B Ballooning degeneration with Mallory-Denk bodies
• C Fibrous expansion of portal tracts with bile duct proliferation
• D Emperipolesis (penetration of inflammatory cells into hepatocyte cytoplasm) and hepatocyte rosetting ✓

Explanation

Emperipolesis (the phenomenon of inflammatory lymphocytes penetrating into and residing within hepatocyte cytoplasm without causing immediate cell death) combined with hepatocyte rosette formation are the most specific histological features of autoimmune hepatitis. These findings, together with interface hepatitis and dense lymphoplasmacytic portal infiltrate, constitute the International AIH Group scoring criteria. Emperipolesis in AIH is distinct from erythrophagocytosis; it is scored as a specific feature in the simplified and revised IAIHG diagnostic criteria.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

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