Autoimmune hepatitis (AIH) is classified into two types by serology. The division describes which autoantibodies are present and, with them, a characteristic patient profile; it is not a claim that the two types are separate diseases. They are not pathologically distinct and do not differ in severity or in response to treatment, and the classification was proposed mainly so that studies could compare similar groups of patients. Its practical value lies in what it predicts about relapse after treatment is stopped.
Type 1
Type 1 AIH is defined by positivity for ANA, SMA, or both, and is much the commoner type. Atypical pANCA is positive in more than 90% of cases.
One or more concurrent autoimmune conditions are very common, most often vitiligo, rheumatoid arthritis (RA), Graves disease, Hashimoto thyroiditis, ulcerative colitis (UC), nephritis and systemic lupus erythematosus (SLE). Which conditions cluster depends on age: thyroid and rheumatic disease are more common in older adults over 60 years, occurring in more than 40% of cases, whereas young adults more often have UC and autoimmune haemolysis, at about 13%.
Type 1 occurs at all ages and is more common in females than males by 3.5-fold. It can present abruptly and acutely with fatigue, jaundice, fever and arthralgia in 25-75% of cases.
Type 2
Type 2 AIH is characterised by positivity for anti-LKM1 and, less commonly, for anti-LC1. Atypical pANCA is mostly negative, which helps separate it from type 1.
Most patients with type 2 AIH are children between 2 and 14 years of age. Concurrent autoimmune conditions are found in about 18% of cases, such as thyroiditis, vitiligo and type 1 diabetes mellitus (DM).
Why the distinction matters
The two types respond to treatment similarly, but patients with type 2 AIH relapse more often after drugs are withdrawn, and they more often need long-term maintenance treatment. Follow-up should therefore be stricter in type 2 disease.