Residency · Residency · Gastroenterology

Autoimmune Hepatitis

Classification

Type 1 AIH (Classic)

Type 1 autoimmune hepatitis accounts for approximately 80% of all AIH cases and can occur at any age, though it demonstrates bimodal peaks of incidence in young women and perimenopausal women. The serologic hallmark is the presence of antinuclear antibodies and/or anti-smooth muscle antibodies. While these autoantibodies are useful for diagnosis, they are neither fully sensitive nor specific for AIH. The anti-soluble liver antigen/liver-pancreas antibody (anti-SLA/LP) is the most specific serologic marker for autoimmune hepatitis, present in 10 to 30% of cases, and is associated with more severe disease and a higher risk of relapse after treatment withdrawal.

Type 2 AIH

Type 2 autoimmune hepatitis accounts for approximately 20% of cases and predominantly affects children and young adults, with a higher prevalence in European populations. The defining autoantibodies are anti-liver-kidney microsomal type 1 antibody (anti-LKM1), which targets cytochrome P450 2D6, and/or anti-liver cytosol type 1 antibody (anti-LC1). Type 2 AIH tends to follow a more aggressive clinical course than type 1, with a higher rate of acute liver failure and a greater propensity for relapse after treatment withdrawal.

Epidemiology

The prevalence of autoimmune hepatitis is estimated at 10 to 25 per 100,000 in Western countries, with a female predominance of approximately 3 to 4:1. The age distribution is bimodal, with peaks at 10 to 30 years and 40 to 60 years, though the disease can present at any age. All ethnicities are affected, but presentation and severity may differ, with evidence suggesting a more aggressive course in African American and Hispanic populations.

Autoimmune hepatitis is frequently associated with other autoimmune conditions. Autoimmune thyroiditis occurs in 10 to 25% of patients, and associations with celiac disease, rheumatoid arthritis, ulcerative colitis, Sjogren syndrome, type 1 diabetes mellitus, and vitiligo are well established. The presence of these comorbid conditions should prompt screening for AIH when unexplained liver enzyme elevations are identified.

Pathogenesis

The pathogenesis of autoimmune hepatitis involves the interaction of genetic susceptibility and environmental triggers culminating in loss of immune tolerance to hepatocyte-derived autoantigens. Genetic predisposition is strongly linked to the human leukocyte antigen system, with HLA-DR3 associated with younger age of onset, more severe disease, and higher relapse rates, and HLA-DR4 associated with older age of onset and potentially better treatment response.

Environmental triggers are postulated to initiate the autoimmune process through molecular mimicry, in which viral infections, drug exposures, or herbal supplements present epitopes that are structurally similar to hepatocyte autoantigens, thereby activating autoreactive T lymphocytes. The effector mechanism of hepatocyte destruction is mediated primarily by CD4-positive T cells through Th1 and Th17 pathways. Defective regulatory T cell function, which normally maintains peripheral tolerance to self-antigens, permits the sustained autoimmune attack that characterizes the disease.

Clinical Presentation

Spectrum

Autoimmune hepatitis demonstrates a remarkably diverse clinical spectrum. Chronic hepatitis is the most common presentation, accounting for approximately 70% of cases. Patients may present insidiously with fatigue, arthralgias, jaundice, and right upper quadrant discomfort that may have been present for weeks to months before medical evaluation.

Acute hepatitis occurs in 25 to 30% of patients and may be indistinguishable from acute viral hepatitis at initial presentation. In 5 to 10% of cases, patients present with fulminant hepatic failure, which is more common in type 2 AIH. A particularly important diagnostic consideration is that autoantibodies may be negative during acute presentations (seronegative AIH), making the diagnosis especially challenging in the fulminant setting.

Some patients are identified incidentally through unexplained transaminase elevation discovered on routine laboratory testing, and significant fibrosis may already be present at the time of diagnosis. Indeed, 30 to 40% of patients already have established cirrhosis at the time of initial diagnosis, reflecting delayed recognition of this disease.

Laboratory Features

The aminotransferases are typically elevated, often exceeding 5 to 10 times the upper limit of normal, and may exceed 1000 IU/L during acute flares. Elevated immunoglobulin G is a characteristic and diagnostically important finding. Polyclonal hypergammaglobulinemia with an IgG level exceeding 1.1 times the upper limit of normal is highly suggestive of autoimmune hepatitis. The IgG level correlates with disease activity and serves as an important monitoring parameter during treatment.

Autoantibody testing is a cornerstone of diagnosis. ANA is positive in 50 to 70% of type 1 AIH but is nonspecific, occurring in MASLD, primary biliary cholangitis, and drug reactions. ASMA is positive in 50 to 70% of type 1 AIH, with the anti-actin subtype being more specific for the diagnosis. Autoantibody titers can fluctuate over time, and low titers do not exclude autoimmune hepatitis. Seronegative AIH, in which standard autoantibodies are negative, occurs in 10 to 20% of cases. This diagnosis should be suspected when typical histologic features are present in combination with elevated IgG and exclusion of alternative etiologies.

Diagnosis

Simplified International AIH Group (IAIHG) Scoring System (2008)

The simplified scoring system developed by the International Autoimmune Hepatitis Group provides a practical framework for diagnosis. Points are assigned based on autoantibody titers: ANA or ASMA at a titer of 1:40 or greater earns 1 point, at 1:80 or greater earns 2 points; anti-LKM1 at 1:40 or greater earns 2 points; and a positive anti-SLA earns 2 points. IgG levels exceeding the upper limit of normal earn 1 point, while levels exceeding 1.1 times the upper limit earn 2 points. Liver histology that is compatible with AIH earns 1 point, while typical histology earns 2 points. The absence of viral hepatitis earns 2 points. A total score of 6 or greater indicates probable AIH, and a score of 7 or greater indicates definite AIH.

Histologic Features

Liver biopsy is strongly recommended for the diagnosis of autoimmune hepatitis, as it establishes disease severity, determines the extent of fibrosis, and permits the exclusion of overlap syndromes. Interface hepatitis, also known as piecemeal necrosis, is the histologic hallmark of AIH and consists of a lymphoplasmacytic infiltrate extending from the portal tracts into the adjacent hepatic parenchyma at the portal-parenchymal junction.

A plasma cell-rich inflammatory infiltrate is prominently featured at both the interface and within the lobular parenchyma. Hepatocyte rosette formation, in which regenerating hepatocytes arrange themselves in circular clusters around a central lumen, is a characteristic finding. Emperipolesis, the active penetration of lymphocytes into hepatocytes, is increasingly recognized as a relatively specific histologic feature.

In acute and severe presentations, centrilobular (zone 3) necrosis may be the predominant histologic pattern, and this feature may dominate the biopsy findings in acute presentations, potentially obscuring the classic interface hepatitis pattern. In advanced disease, bridging fibrosis and cirrhosis are observed.

Differential Diagnosis

Drug-induced liver injury represents the most important diagnostic differential, particularly with agents such as minocycline, nitrofurantoin, statins, methyldopa, infliximab, and immune checkpoint inhibitors, all of which can produce an AIH-like picture that may be histologically indistinguishable from idiopathic AIH. A thorough medication history, including over-the-counter products and supplements, is essential.

Wilson disease must be excluded in all patients under 40 years of age through measurement of serum ceruloplasmin, 24-hour urine copper, and ophthalmologic examination for Kayser-Fleischer rings. Viral hepatitis (HAV, HBV, HCV, HEV) should be excluded with appropriate serologic and molecular testing. Overlap with primary biliary cholangitis and primary sclerosing cholangitis must be considered, and MASLD with autoimmune features may mimic AIH in some patients.

<image>A histopathological illustration of autoimmune hepatitis showing the key diagnostic features. Central panel: low-power view of a liver biopsy with a portal tract showing dense lymphoplasmacytic interface hepatitis — inflammatory cells spilling from the portal tract into the surrounding hepatic parenchyma. Label the portal tract structures (portal vein, hepatic artery, bile duct) and the interface hepatitis zone. Four high-power insets arranged around the central panel: (1) "Plasma cell-rich infiltrate": cluster of plasma cells with eccentric nuclei, clock-face chromatin, and perinuclear hof; (2) "Hepatocyte rosettes": regenerating hepatocytes arranged in a circular rosette pattern around a central space; (3) "Emperipolesis": a lymphocyte visibly penetrating into a hepatocyte cytoplasm with intact hepatocyte membrane; (4) "Zone 3 necrosis": centrilobular hepatocyte dropout with inflammatory infiltrate surrounding the central vein. Use H&E stain coloring: pink hepatocyte cytoplasm, purple nuclei, darker purple plasma cell clumps. Include a Masson trichrome inset showing bridging fibrosis (blue bands connecting portal tracts to central veins). Label all features with leader lines and annotations.</image>

Treatment

Indications for Treatment

Treatment is indicated for patients with elevated aminotransferases exceeding 3 to 5 times the upper limit of normal, with or without symptoms; elevated IgG exceeding 2 times the upper limit of normal; histologic evidence of interface hepatitis or bridging necrosis; or symptoms attributable to autoimmune hepatitis. Even patients with apparently mild disease may benefit from treatment to prevent progression, as untreated severe autoimmune hepatitis carries a 50% 5-year mortality.

Induction Therapy

The preferred induction regimen combines prednisone (or prednisolone) with azathioprine. Prednisone is initiated at 40 to 60 mg per day and tapered over 4 to 8 weeks to a maintenance dose of 5 to 10 mg per day. Azathioprine is typically started at 50 mg per day, ideally after 2 weeks of prednisone monotherapy. This delayed initiation is strategically important because it prevents confusion between azathioprine-induced hepatotoxicity and disease non-response. Once initiated, azathioprine is titrated to 1 to 2 mg/kg/day based on tolerance and treatment response. TPMT and NUDT15 genotyping must be performed before starting azathioprine to identify patients at risk for severe myelosuppression, following the same principles applied in inflammatory bowel disease management.

Prednisone monotherapy at 60 mg per day with a gradual taper is an alternative when azathioprine is not tolerated or is contraindicated, though higher steroid doses are required, resulting in more side effects. A budesonide-based regimen, using budesonide 9 mg per day combined with azathioprine, offers fewer systemic steroid effects including less cortisol suppression, weight gain, and bone loss. However, budesonide is contraindicated in patients with cirrhosis because portal-systemic shunting bypasses hepatic first-pass metabolism, resulting in significant systemic exposure and loss of the favorable side effect profile.

Treatment Response

Aminotransferases should begin to decline within 2 to 4 weeks of initiating therapy and should normalize within 3 to 6 months in most patients. Normalization of IgG is an important treatment target, as it correlates with histologic remission and indicates adequate disease control. Biochemical remission is defined as normal ALT and normal IgG. Histologic remission, defined as resolution of interface hepatitis on repeat biopsy, characteristically lags behind biochemical improvement by 3 to 8 months.

Patients who do not achieve complete biochemical normalization by 6 months should have their azathioprine dose optimized to 2 mg/kg/day and their steroid dose adjusted. If the response remains inadequate, transition to alternative immunosuppressive agents should be considered.

Maintenance Therapy

Azathioprine at 1 to 2 mg/kg/day serves as the steroid-sparing maintenance agent, with the goal of maintaining prednisone at 10 mg per day or less, or withdrawing steroids entirely. Sustained normalization of both ALT and IgG for at least 2 years should be achieved before considering treatment withdrawal.

Treatment duration is typically lifelong in most patients. A withdrawal attempt may be considered after 2 to 3 or more years of complete remission, encompassing normal ALT, normal IgG, and histologic remission confirmed by liver biopsy. However, the relapse rate after treatment withdrawal is 50 to 90% overall and is higher in type 2 AIH, HLA-DR3-positive patients, those with cirrhosis, and those with incomplete histologic remission. When relapse occurs, reinduction with prednisone and azathioprine is usually effective, but lifelong maintenance therapy is then advisable.

Second-Line Therapy

Mycophenolate mofetil at 1.5 to 2 grams per day is the primary second-line agent for patients who are intolerant of azathioprine or do not respond adequately. It is teratogenic and must not be used in women of childbearing potential without reliable contraception. 6-Mercaptopurine represents an alternative thiopurine, as some patients who cannot tolerate azathioprine are able to tolerate 6-MP.

Tacrolimus at 1 to 4 mg twice daily (target trough 3 to 6 ng/mL) is a calcineurin inhibitor used for refractory AIH. Cyclosporine has been employed in acute severe and fulminant AIH as a bridge to transplant or, in some cases, to avoid transplant altogether. Rituximab, an anti-CD20 monoclonal antibody that depletes B cells, has been reported in case series for refractory AIH. Infliximab has also been used, though it should be noted that anti-TNF agents can paradoxically cause drug-induced AIH-like liver injury.

AIH and Acute Liver Failure

Autoimmune hepatitis accounts for 3 to 6% of acute liver failure cases and frequently presents with negative autoantibodies in the acute setting, making diagnosis challenging. Very high ALT values exceeding 1000 IU/L, elevated IgG, and plasma cell-rich centrilobular necrosis on liver biopsy (obtained by the transjugular approach if the patient is coagulopathic) provide important diagnostic clues.

A corticosteroid trial is controversial but may be attempted with intravenous methylprednisolone at 60 mg per day, with close monitoring for clinical improvement over 7 to 14 days. If there is no improvement in MELD score or INR by day 7, the patient should proceed to liver transplantation without further delay, as prolonged immunosuppression in the face of progressive hepatic failure carries unacceptable risk. The King's College Criteria for acute liver failure are applicable for transplant decision-making.

Overlap Syndromes

AIH-PBC Overlap

The overlap of autoimmune hepatitis and primary biliary cholangitis is characterized by features of both diseases: interface hepatitis, elevated IgG, and positive ANA or ASMA consistent with AIH, alongside AMA positivity, elevated alkaline phosphatase and GGT, and florid duct lesions consistent with PBC. The Paris criteria require that 2 of 3 features of each disease be present for the diagnosis. Treatment requires the combination of ursodeoxycholic acid at 13 to 15 mg/kg/day plus immunosuppression with prednisone and azathioprine. UDCA alone is insufficient to control the autoimmune hepatitis component.

AIH-PSC Overlap

The overlap of autoimmune hepatitis and primary sclerosing cholangitis is more common in children and adolescents, in whom it is sometimes termed autoimmune sclerosing cholangitis. Diagnosis requires features of AIH in combination with cholangiographic evidence of PSC, such as beading and stricturing of bile ducts demonstrated on magnetic resonance cholangiopancreatography. Treatment involves the combination of immunosuppression for the AIH component and UDCA, though the role of UDCA in PSC remains controversial.

Special Populations

Pregnancy

Autoimmune hepatitis often improves during pregnancy owing to the physiologic state of immune tolerance, but disease flares occur in 30 to 50% of patients in the postpartum period. Azathioprine should be continued during pregnancy, as the benefits of disease control outweigh the theoretical teratogenic risk. While classified as category D, extensive data from the inflammatory bowel disease literature support its safety during pregnancy. Mycophenolate mofetil is absolutely contraindicated in pregnancy (category X) and must be discontinued before conception. Low-dose prednisone is safe during pregnancy.

Post-Transplant AIH

Recurrent autoimmune hepatitis occurs in 20 to 40% of patients after liver transplantation. De novo AIH, in which autoimmune hepatitis develops in the transplanted liver without prior history of the disease, is recognized particularly in pediatric transplant recipients. Both forms are managed through optimization of immunosuppression.

<image>A treatment algorithm for autoimmune hepatitis. Start with "Confirmed AIH diagnosis (simplified IAIHG score >= 6-7 + liver biopsy)." First decision: "Severity assessment." Branch 1 "Acute/Severe (ALT > 10x ULN, marked jaundice, or ALF features)": "IV methylprednisolone 60 mg/day; assess response at day 7; if no improvement, urgent transplant evaluation." Branch 2 "Moderate (ALT 3-10x ULN)": "Prednisone 40-60 mg/day + AZA 50 mg/day (check TPMT/NUDT15 first; add AZA after 2 weeks if preferred)." Branch 3 "Mild (ALT 1-3x ULN, interface hepatitis on biopsy)": "Prednisone 20-30 mg/day + AZA; or budesonide 9 mg/day + AZA (if NON-cirrhotic)." For all treated patients, show treatment response assessment at 4-8 weeks: "ALT declining, IgG trending to normal?" If yes: "Taper prednisone to <=10 mg/day over 8-12 weeks; maintain AZA 1-2 mg/kg/day." If no: "Dose optimize (increase AZA, ensure compliance); if AZA intolerant, switch to MMF 1.5-2 g/day." Long-term pathway: "Maintain normal ALT + IgG for >= 2-3 years -> consider withdrawal attempt (biopsy before withdrawal to confirm histologic remission) -> relapse rate 50-90% -> likely lifelong therapy." Use green for response, red for non-response/ALF, yellow for ongoing monitoring.</image>

Key Clinical Pearls

• AIH must be considered in all cases of acute liver failure. Autoantibodies may be negative in acute presentations, and elevated IgG with plasma cell-rich interface or centrilobular necrosis on biopsy are the diagnostic clues.
• IgG level is the most important biochemical target during treatment. Normalization correlates with histologic remission.
• Azathioprine hepatotoxicity occurs in 3 to 10% of patients. Starting azathioprine after 2 weeks of prednisone monotherapy helps distinguish drug toxicity from disease non-response.
• TPMT/NUDT15 genotyping is mandatory before initiating azathioprine.
• Budesonide is an alternative to systemic steroids but is contraindicated in cirrhosis because first-pass metabolism is bypassed by portal-systemic shunting.
• Relapse after treatment withdrawal is extremely common (50 to 90%). Most patients require lifelong immunosuppression.
• Drug-induced AIH (minocycline, nitrofurantoin, checkpoint inhibitors) may be indistinguishable from idiopathic AIH. A thorough medication history review is essential.
• AIH-PBC overlap requires combination therapy (UDCA plus immunosuppression). UDCA alone is insufficient.

References

1. Mack CL, et al. Diagnosis and management of autoimmune hepatitis in adults and children: 2019 practice guidance and guidelines from the AASLD. Hepatology. 2020;72(2):671-722.
2. Hennes EM, et al. Simplified criteria for the diagnosis of autoimmune hepatitis. Hepatology. 2008;48(1):169-176.
3. European Association for the Study of the Liver. EASL Clinical Practice Guidelines: Autoimmune Hepatitis. J Hepatol. 2015;63(4):971-1004.
4. Heneghan MA, et al. Autoimmune hepatitis. Lancet. 2013;382(9902):1433-1444.
5. Lohse AW, et al. Budesonide in the treatment of autoimmune hepatitis: a randomized controlled trial. Gastroenterology. 2010;139(4):1198-1206.

Read this lecture as Markdown