What is Autoimmune Hepatitis (AIH)?
Autoimmune hepatitis is an immune-mediated chronic inflammatory liver disease of unknown cause, characterized by elevated liver enzymes (AST/ALT), increased serum IgG levels, presence of specific autoantibodies, and interface hepatitis on liver biopsy, which responds favorably to immunosuppressive therapy 1, 2.
Key Diagnostic Features
AIH is fundamentally a clinicopathological diagnosis requiring the convergence of multiple findings 1:
Laboratory Abnormalities
- Elevated aminotransferases (AST and ALT)
- Hypergammaglobulinemia, particularly elevated IgG levels
- Positive autoantibodies (see below)
Autoantibody Patterns
The disease is classified into two types based on autoantibody profiles 2:
Type 1 AIH (most common in adults):
- Antinuclear antibodies (ANA) - present in 80% of cases
- Smooth muscle antibodies (SMA)/anti-actin antibodies - present in 63%
- Anti-soluble liver antigen (anti-SLA) - present in 7-22%
Type 2 AIH (predominantly in children):
- Anti-liver kidney microsome type 1 (anti-LKM1) antibodies - present in 3% of adults
- Anti-liver cytosol type 1 antibodies
Histological Features
Liver biopsy is essential and shows 1, 3:
- Interface hepatitis (hallmark finding)
- Lymphoplasmacytic portal infiltrate with plasma cells
- Portal-based fibrosis
- More than mild lobular hepatitis
Clinical Presentation Spectrum
AIH presents with remarkable heterogeneity 1, 4:
- Asymptomatic with incidental enzyme elevation
- Chronic indolent disease with fatigue and jaundice
- Acute/acute-onset AIH mimicking acute hepatitis
- Fulminant presentation with acute liver failure
- Cirrhosis at diagnosis in unrecognized cases
Diagnostic Approach
The simplified diagnostic criteria (2008) are recommended for clinical practice 1. This system scores four variables:
- Autoantibodies: ANA or SMA ≥1:40 (1 point); ≥1:80 (2 points); or anti-LKM1 ≥1:40 (2 points)
- IgG levels: >upper limit of normal (1 point); >1.1× upper limit (2 points)
- Liver histology: Compatible (1 point); typical (2 points)
- Viral hepatitis exclusion: Negative (2 points)
Scoring interpretation:
- ≥7 points = definite AIH
- ≥6 points = probable AIH
This simplified system has >90% sensitivity and specificity 1.
Critical Diagnostic Caveats
The simplified criteria have limited accuracy in specific situations 1:
- Acute-onset AIH presentations
- Drug-induced autoimmune-like hepatitis
- Variant/overlap syndromes
- Concurrent liver diseases (MASLD, viral hepatitis, alcohol-related disease, Wilson's disease)
In these scenarios, expert hepatologist and pathologist evaluation is mandatory.
Seronegative AIH
Up to 20% of AIH cases are negative for conventional autoantibodies (ANA, SMA, anti-LKM1) 2. When seronegative AIH is suspected, additional testing for atypical autoantibodies (anti-SLA, atypical pANCA) should be pursued.
Disease Complications
Acute Complications
- Acute liver failure in fulminant presentations
- Acute-on-chronic liver failure (can be precipitated by stopping immunosuppression)
Chronic Complications
- Cirrhosis in untreated or inadequately treated patients
- Hepatic decompensation
- Hepatocellular carcinoma - occurs in 1-9% of AIH-related cirrhosis (significantly lower than other liver diseases) 1
Essential Exclusions
AIH diagnosis requires excluding 2, 5:
- Viral hepatitis (hepatitis B, C, D, E)
- Drug-induced liver injury
- Wilson's disease
- Hereditary hemochromatosis
- Alcoholic liver disease
- Metabolic liver diseases (especially in children)
- Non-alcoholic fatty liver disease/NASH
Epidemiology
AIH affects all ages, ethnic groups, and both sexes, though there is female preponderance 6. The prevalence is increasing globally, including in Japan and Western countries 4.
Genetic Associations
Type 1 AIH is associated with HLA DRB103 (all ages) and DRB104 (late-onset disease) 6.
Type 2 AIH is associated with HLA DRB107 and DRB103 6.
Common Pitfall
The high prevalence of MASLD and alcohol consumption makes coexistence with AIH common 1. Do not dismiss AIH diagnosis simply because metabolic or alcohol-related features are present—these can coexist and require careful clinicopathological correlation.