Autoimmune hepatitis (AIH) (plural: autoimmune hepatitides) is a rare type of chronic hepatitis, currently classified as "type 1" or "type 2". It may eventually lead to cirrhosis. The role of imaging is primarily to exclude other diagnoses and evaluate for complications.
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Epidemiology
It may occur in children or adults, but most patients are affected at 40-60 years old. The incidence in Western Europe is ~0.01-0.02% 2. There is no predilection for an ethnic group.
There is a female predominance: 3.6: 1.
Clinical presentation
Autoimmune hepatitis has a variable clinical presentation. Patients may be asymptomatic or present in acute liver failure (rare), or anywhere between. It tends to have a relapsing-remitting course. There is an association with other autoimmune conditions.
Depending on the phase, the patient may present with
- hepatomegaly +/- splenomegaly
- jaundice
- elevated aminotransferases (ALT and AST)
Diagnostic criteria of autoimmune hepatitis include:
- elevated antinuclear antibodies,antismooth muscle antibodies
- globulin level of more than 20 g/L
- coexistence of non-hepatic autoimmune diseases, including autoimmune thyroiditis, rheumatoid arthritis, and systemic lupus
- the elimination of other forms of hepatitis such as viral or toxic hepatitis
- histologic examination findings consistent with AIH
Pathology
Autoimmune liver diseases are classified into:
There may be an overlap between those types especially between autoimmune hepatitis and primary sclerosing cholangitis, the so-called overlap syndrome.
Autoimmune hepatitis may encompass multiple different conditions.
Type 1:
- "classic" autoimmune hepatitis
- ANA, IgG4, and anti-smooth muscle antibody may be elevated, with the last (1:320) a relatively more specific finding in type 1
- ANCA is more often found in type 1 than in type 2
Type 2:
- has antibodies to liver/kidney microsomes (ALKM-1) or to a liver cytosolic antigen (ALC-1)
Biopsy and histopathology is less specific for a diagnosis, compared to serum markers.
Radiographic features
The role of imaging in a patient with possible autoimmune hepatitis is threefold:
- to exclude other possibilities of chronic hepatitis
- to look for complications of cirrhosis (such as HCC)
- to look for autoimmune involvement of other organs (such as the pancreas).
CT and MRI
Non-specific, ranging from normal to hepatomegaly and cirrhosis.
Common criteria include:
- hepatic steatosis is evident by lesions of low attenuation (<10 HU attenuation in the non-contrast phase and <25 HU in the portal venous phase). On MRI lesions appear of low signal on fat sat sequences and On T1 dual-echo sequence, the signal intensity on the out-of-phase sequence is reduced by >20% as compared to the in-phase sequences.
- fibrosis manifested as reticular or confluent areas of delayed enhancement
- presence of porta hepatis and portocaval lymph nodes
- intrahepatic biliary radicle dilatation mainly in the overlap syndrome, autoimmune hepatitis, and primary sclerosing cholangitis are the most common overlap syndrome
- heterogeneous parenchymal enhancement which could be patchy, reticular, segmental, or lobar
- patchy early enhancement after contrast administration with no contrast washout on the delayed phase has been attributed to recent hepatocellular damage and intense inflammatory infiltrates
- fibrotic stage: evident by ascites, expanded gallbladder fossa, spleen size, and enlarged preportal space
Differential diagnosis
Autoimmune hepatitis should be differentiated from viral hepatitis, alcoholic hepatitis, and non-alcoholic fatty liver disease. It should also be differentiated from:
- primary biliary cholangitis
- primary sclerosing cholangitis
- acute hepatitis from other etiologies
- Wilson disease (mostly pediatric patients)
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