Primary Biliary Cholangitis: 2018 Practice Guidance from the American Association for the Study of Liver Diseases
Authors: Keith D. Lindor, Christopher L. Bowlus, James Boyer, Cynthia Levy, Marlyn Mayo
Journal: Hepatology (2018)

The funding for the development of this Practice Guidance was provided by the American Association for the Study of Liver Diseases.This practice guidance was approved by the American Association for the Study of Liver Diseases on April 26, 2018. Preamble This American Association for the Study of Liver Diseases (AASLD) 2018 Practice Guidance on Primary Biliary Cholangitis (PBC) is an update of the PBC guidelines published in 2009. The 2018 updated guidance on PBC includes updates on etiology and diagnosis, role of imaging, clinical manifestations, and treatment of PBC since 2009. The AASLD 2018 PBC Guidance provides a data‐supported approach to screening, diagnosis, and clinical management of patients with PBC. It differs from more recent AASLD practice guidelines, which are supported by systematic reviews and a multidisciplinary panel of experts that rates the quality (level) of the evidence and the strength of each recommendation using the Grading of Recommendations Assessment, Development, and Evaluation system. In contrast, this guidance was developed by consensus of an expert panel and provides guidance statements based on formal review and analysis of published literature on the topics. The quality (level) of the evidence and the strength of each guidance statement are not rated. Intended for use by health care providers, this guidance identifies preferred approaches to the diagnostic and therapeutic aspects of care for patients with PBC. As with clinical practice guidelines, it provides general guidance to optimize the care of the majority of patients and should not replace clinical judgment for a unique patient. The major changes from the last guideline to this guidance include information about obeticholic acid (OCA) and the adaptation of the guidance format. Etiology of Primary Biliary Cholangitis Primary Biliary Cholangitis (PBC) is considered an autoimmune disease because of its hallmark serologic signature, antimitochondrial antibody (AMA), and specific bile duct pathology.1The etiology of PBC is thought to be due to a combination of genetic risk factors and environmental triggers.5 AMA is a highly disease‐specific autoantibody8 that targets the lipoic acid present on the 2‐oxo‐acid dehydrogenase complexes located on the inner mitochondrial membrane.9 In addition to a loss in humoral tolerance, there is an increase of autoreactive cluster of differentiation (CD)4+CD8+ pyruvate dehydrogenase complex (PDC‐E2)‐specific T cells in the liver.10 In addition to the high concordance among monozygotic twins compared with dizygotic twins with PBC5, the strong association with human leukocyte antigen alleles, which vary by ethnicity, supports a genetic cause of inherited risk.12 Despite progress, only an estimated 15% of the variability of the disease has been accounted for by genetic studies.21 Environmental risks have been suggested by several large case‐control cohort studies that have found associations with urinary tract infections, reproductive hormone replacement, nail polish, and past cigarette smoking.22 Studies of geographic clustering have suggested environmental exposure and socioeconomic factors as well.25 The interaction between genetic and environmental effects has only begun to be assessed in PBC, with several possible gene‐modifying mechanisms being supported.15 Specific environmental agents that may lead to the loss of tolerance of PDC‐E2 are xenobiotics that may either mimic or modify lipoic acid, such as 2‐octynoic acid, which is common in cosmetics, and 6,8‐bis (acetylthio) octanoic acid, a metabolite of acetaminophen. AMA‐positive serum from PBC patients strongly cross‐reacts with these xenobiotics.30 Further experimental support for the role of xenobiotics in PBC pathogenesis comes from the ability of xenobiotics to induce a PBC‐like pathology, including AMA, in animal models.32 The enigma of PBC pathogenesis has been the specific targeting of the biliary epithelial cells in the setting of a ubiquitous autoantigen. The majority of AMA produced by plasmablasts is immunoglobulin A (IgA), which may undergo transcytosis through the biliary epithelium and disrupt mitochondrial function. Alternatively, the specificity of the immune attack may be due to the incomplete proteolysis of pyruvate dehydrogenase complex PDC‐E2 and other mitochondrial enzymes during apoptosis of biliary epithelial cells, a unique feature of this cell type.17 Taken together, the evidence strongly supports the antimitochondrial response as a direct effector of the liver pathology, although other nonautoimmune mechanisms may play a role as well. Natural History PBC is a chronic cholestatic disease with a progressive course that may extend over many decades. The rate of progression varies greatly among individual patients. Over the past decades, there have been many changes in the diagnosis and management of PBC. More patients are being recognized with earlier‐stage disease, and many of these patients respond well to medical therapy. In both Europe and North America, the number of liver transplants for PBC is falling.35 However, the overall prevalence of the disease is increasing.37 Patterns of Clinical Disease and Natural History in the Pre‐Ursodeoxycholic Acid Era The overall prevalence of AMA positivity in various populations is not well known. It is estimated that 0.5% of the general population in Italy are AMA positive.38 In a study from Japan, 11 of 1,714 people (0.64%) were AMA positive.39 AMA may be detectable in serum when patients are symptom free and liver tests are normal.40 Long‐term follow‐up of 229 AMA‐positive individuals for up to 7 years found that the 5‐year incidence of PBC was 16%. In a smaller study, the median time from the first positive AMA test to persistently abnormal liver tests was 6 years, with a range between 1 and 19 years; none of these patients developed cirrhosis during the follow‐up.41 The overall prevalence of clinical disease in various populations has been difficult to estimate because of the rarity of the disease. Estimates vary between 19 and 402 cases of PBC per million.3 One recent paper has shown an overall prevalence of 290 per million, with a prevalence of 430 per million in women and 110 per million in men as opposed to other studies suggesting a 9:1 ratio of women to men.42 PBC may affect all races and ethnicities, with most data collected from the Caucasian population. The prevalence of AMA positivity in first‐degree relatives (FDRs) of PBC patients is increased compared with controls (13.1% and 1%, respectively). Greater prevalence of AMA was found in female FDRs of PBC probands (sisters [20.7%], mothers [15.1%], and daughters [9.8%]) than in male FDRs (brothers [7.8%], fathers [3.7%], and sons [0%]).43 Asymptomatic Versus Symptomatic PBC The proportion of asymptomatic patients (which has been variably defined) who will subsequently develop PBC‐related symptoms has been investigated in several series from the United Kingdom, North America, and Sweden.44 All of these studies provide evidence of progressive disease in a substantial proportion of patients, with between 36% and 89% becoming symptomatic during average follow‐up periods ranging from 4.5 to 17.8 years and a median time from diagnosis to the appearance of symptoms between 2 and 4.2 years.45 In the absence of ursodeoxycholic acid (UDCA) therapy, patients have a significantly shortened survival compared with a healthy population regardless of symptoms.48 The 10‐year survival of asymptomatic patients in three series ranged from 50% to 70%, whereas the median duration of survival for symptomatic patients ranged from 5 to 8 years from the onset of symptoms.45 In an early study of 279 patients from the United States50 followed for 24 years, the median survival of symptomatic patients was 7.5 years, much shorter than the median survival of 16 years for asymptomatic patients. This marked difference in survival was not found in the study from northeast England, a finding possibly explained by an excess of deaths unrelated to liver disease in older asymptomatic patients or possibly because referrals to subspecialists were made only when patients became symptomatic.51 Disease Progression Histologic stages have been found to predict survival.50 The rate of histologic progression has been assessed in three large groups of patients in the absence of a therapeutically effective agent.52 The median time to develop extensive fibrosis (≥F3) was 2 years. After 4 years, the probability of remaining in the early stage of PBC was 29% (confidence interval [CI], 15%‐52%), while cirrhosis was diagnosed in 50% of patients who initially had only interface hepatitis without fibrosis. Only a minority (20%) of patients who were precirrhotic showed histologic stability. On average, the histologic stage progressed by 1 stage every 1.5 years.54 The development of decompensated liver disease (ascites, bleeding, hepatic encephalopathy, or hyperbilirubinemia [>6 mg/dL]) during a follow‐up of 5 years has been estimated to be 15% in a large community‐based study of 770 patients in northeast England48 and 25% of the 236 patients enrolled in a European clinical trial of azathioprine.52 About half of the patients in both studies had cirrhosis at entry. The rate of development of esophageal varices and its impact on survival were evaluated in a prospective study of 256 patients (28% of whom had cirrhosis) observed for a median time of 5.6 years.55 A total of 31% of patients developed esophageal varices. After the development of varices, the 3‐year survival was 59%, whereas after a first bleeding episode, it was 46%. Natural History in the UDCA Era (CIRCA 1990) UDCA was the first and only drug approved for the treatment of patients with PBC in the United States until 2016, when OCA was approved by the Food and Drug Administration. Several randomized trials, combined analyses, and long‐term observational studies have shown that UDCA not only improves biochemical indices but also delays histologic progression and improves survival without transplantation.53 Accordingly, UDCA is the initial drug of choice for PBC therapy. In an early study, the rate of histologic progression to cirrhosis was significantly lower in the UDCA group than in the control group (13% versus 49%).56 In a trial involving 192 patients, UDCA therapy significantly delayed histologic stage progression after a median follow‐up of 3.4 years.60 In a French study of UDCA, the risk of progression per year from stages I‐II to stages III‐IV was 7% ± 2% with UDCA and 34% ± 9% with placebo.53 Predictive factors for the development of cirrhosis included serum bilirubin greater than 1 mg/dL and moderate to severe lymphocytic piecemeal necrosis on the liver biopsy.68 The effect of UDCA therapy on the development of esophageal varices was addressed in a prospective study of 180 patients who received UDCA versus placebo and were observed for up to 4 years69; a total of 139 patients had no varices, and 41 had varices at baseline. After 4 years, the risk of developing varices was 16% for the UDCA‐treated patients and 58% for those receiving the placebo. However, UDCA did not reduce the rate of bleeding, which was low in both groups. Survival Prognostic Models Early natural history models evolved in the pre‐UDCA era. The first PBC‐specific model was proposed by Roll et al. in 1983 (the Yale model) based on a retrospective study of 280 patients observed over a period of 19 years. Age, serum bilirubin, hepatomegaly, and advanced fibrosis or cirrhosis were independent risk factors for a poorer prognosis. However, this model required liver biopsy, limiting its usefulness.50 In 1985, Christensen et al. presented a European model also requiring liver biopsy.70Once the Mayo model was introduced by Dickson, prognosis could be estimated without the need for biopsy.71 Following the introduction of UDCA therapy, a series of models—which are summarized in recent reviews72 and most of which were based on alkaline phosphatase (ALP) responses to treatment—ensued. The two most recent prognostic models, the GLOBE score and the UK‐PBC score, are based on larger sample sizes obtained from and derived from multiple centers. The GLOBE score was developed from a retrospective cohort of 2,488 UDCA‐treated patients and validated by a second cohort of 1,631 European and North American patients.74 The score included the following five variables: serum bilirubin, albumin, ALP, platelet count after 1 year of treatment (https://www.globalpbc.com/globe), and age at start of therapy. Patients with a score greater than 0.30 had a shorter transplantation‐free survival than an age‐ and sex‐matched healthy population. The UK‐PBC score involved a cohort of 3,165 patients and found that serum ALP, amino transferases, and bilirubin after 12 months of therapy—as well as albumin and platelets at baseline—predicted the risk of a liver transplant or liver‐related death occurring within 5, 10, or 15 years.75 Both the GLOBE and UK‐PBC scores are superior to prior models, although validation in other ethnic groups and populations is needed. Other Predictions of Prognosis The bilirubin level is the best predictor of survival and is the most important component in all mathematical models of prognosis in PBC.71 Serum ALP less than twice the upper limit of normal with treatment is a reliable predictor of treatment response.77 Transient elastography is emerging as a technique to assess prognosis and treatment response as well.80 Diagnosis of PBC The diagnosis of PBC should be suspected in the setting of chronic cholestasis after exclusion of other causes of liver disease, particularly in a middle‐aged female with an unexplained elevation of serum ALP. The diagnosis is largely confirmed with tests for AMA. A liver biopsy can be used to further substantiate the diagnosis but is rarely needed.81 Liver Biochemical Tests Most patients with PBC have abnormal liver tests including elevations of ALP, mild elevations of aminotransferase (alanine aminotransferase or aspartate aminotransferase) activity, and increased levels of immunoglobulins (mainly IgM). Some patients with PBC may have high alanine aminotransferase or aspartate aminotransferase activities associated with hyper‐γ‐globulinemia (elevated IgG). The magnitude of biochemical test elevations is loosely related to the severity of the disease.70 In patients without cirrhosis, the degree of elevation in ALP is strongly related to the severity of ductopenia and inflammation; the increase in aminotransferase activity and IgG levels mainly reflects the degree of periportal and lobular necrosis and inflammation; and hyperbilirubinemia reflects the severity of ductopenia and biliary piecemeal necrosis. A rise in serum bilirubin, ‐globulins, and hyaluronic acid together with a fall in serum albumin and platelet count are the early indicators of the development of cirrhosis and portal hypertension.82 As in other cholestatic diseases, serum cholesterol levels are often elevated.84 Individual serum bile acid levels can be elevated but are not routinely determined. Autoantibodies AMA is found in 95% of PBC patients.85 Antinuclear antibody and anti‐smooth muscle antibody are found in nearly half.85 In approximately 5% to 10% of the patients, AMA is absent or present only in low titer (≤1/80), when immunofluorescent techniques are used. The presence or absence of AMA, rather than the magnitude of antibody level, is most important in diagnosis. In some patients, antinuclear antibodies, particularly anti‐glycoprotein 210 (anti‐gp210) and/or anti‐sp100, are present and may correlate with prognosis86; in some other AMA‐negative patients, antibodies against the major M2 components (PDC‐E2 and 2‐oxoglutaric acid dehydrogenase complex), are present using enzyme‐linked immunosorbent assay or Western blotting techniques. There are five common strategies for detecting AMA in clinical practice, including indirect immunofluorescence, immunoblotting, enzyme immunoassay, Luminex beads assay, and enzyme inhibition assay. The indirect immunofluorescence method has the lowest sensitivity, with over 15% of AMA‐negative sera by indirect immunofluorescence showing reactivity to MIT3, a combination of three mitochondrial antigens.87 In addition, nearly all AMA‐negative PBC patients have PBC‐specific antinuclear antibodies, including sp100 and gp210, which are present in over 30% of PBC patients negative for AMA by indirect immunofluorescence. More recently, anti‐kelch‐like 12 and anti‐hexokinase 1 have been found in 35% and 22% of AMA‐negative PBC patients, respectively, but these are not yet widely available.88 There are weak correlations between the values obtained with these various methods; however, the methods agree well on whether AMA is positive or negative. A previously mentioned study of 229 individuals without an established diagnosis of PBC followed subjects for up to 7 years and found a 5‐year incidence rate of PBC of 16%. The overall conclusion from this study was that only 1 in 6 patients with a positive AMA and normal ALP will develop PBC after 5 years. If liver tests are initially normal, following these patients at 2‐ to 3‐year intervals until age 65 seems reasonable, but there are no data regarding this.40 Histology Liver biopsy is no longer required for diagnosis in most patients. Histologically, PBC is characterized by chronic, nonsuppurative cholangitis that mainly affects interlobular and septal bile ducts. When focal lesions show intense inflammatory changes and necrosis around bile ducts, the term "florid duct lesion" is often used. The inflammatory infiltrate is in close contact with the basal membrane of cholangiocytes undergoing necrosis and consists of plasma cells, macrophages, and polymorphonuclear cells (especially eosinophils). In some cases, epithelioid granulomas are present, more often in the early stage of disease.85 There are few (if any) arterial lesions. In contrast, portal venules are often compressed and occluded by the inflammatory reaction. Terminal hepatic venules are often retained in their central location with progression of fibrosis and sometimes even in cirrhosis. Bile duct paucity or ductopenia is usually defined as when fewer than 50% of portal tracts contain bile ducts. The size of the liver biopsy specimen is important. The probability of observing cholangitis and bile duct destruction increases with the number of portal tracts because of the typical patchy distribution of the lesions. At least 10 to 15 portal tracts should be present, and multiple sections should be reviewed to adequately appreciate or rule out cholangitis and ductopenia. These findings would include periportal and/or periseptal copper deposition, periportal and/or periseptal feathery degeneration with or without Mallory‐Denk bodies, and cholestatic rosettes. Actual bile stasis is not appreciated until decompensated liver disease has occurred. Histologic lesions are classically divided into 4 stages (Fig. 1). Stage I is characterized by portal inflammation with or without florid bile duct lesions. In this stage, inflammation remains confined to the portal triads. Disease progression is characterized by the gradual increase of periportal lesions extending into the hepatic parenchyma, referred to as interface hepatitis (stage II). Periportal regions become focally irregular, and the lesion is characterized by cellular necrosis or apoptosis, separation of hepatocytes by inflammatory cells, and macrophages. There are two main types of interface hepatitis. The first is lymphocytic piecemeal necrosis, which is the association of hepatocellular necrosis or apoptosis with lymphohistiocytic cells. This is similar to the lesion found in autoimmune hepatitis (AIH). Second is biliary piecemeal necrosis, which is marked by a striking ductular reaction—sometimes referred to as ductular proliferation—and is accompanied by edema, neutrophil infiltration, periductular fibrosis, and necrotic hepatocytes, the latter associated with cholestasis. Studies of French PBC patients have shown that severity of interface hepatitis is highly predictive of development of extensive fibrosis.67 Stage III is characterized by a distortion of the hepatic architecture with numerous fibrous septa. Cirrhosis with the existence of regenerative nodules defines stage IV. Nakanuma et al. recently introduced a system that assesses bile duct loss, fibrosis, and cholestasis to develop a 4‐stage model.90 Nodular regenerative hyperplasia is a known complication of PBC and should be differentiated from cirrhosis; it may also contribute to portal hypertension in noncirrhotic patients.91Figure 1: (A) Stage 1 PBC with portal inflammation and a florid ductal lesion; hematoxylin‐eosin, magnification 20x. (B) Stage 2 PBC with portal inflammation, focal interface hepatitis, and bile ductular proliferation; hematoxylin‐eosin, magnification 40x. (C) Stage 3 PBC with bridging inflammation; hematoxylin‐eosin, magnification 20x. (D) Stage 4 PBC showing cirrhosis with ductopenia; hematoxylin‐eosin, magnification 20x. Courtesy of Dr Monica Tulia Garcia‐Buitrago. [Correction added on December 17, 2018, after first online publication: Acknowledgment for Dr Monica Tulia Garcia‐Buitrago was added.]With the high disease specificity of a positive AMA test, the role of liver biopsy in diagnosing PBC is questionable when ALP activity is at least 1.5 times the normal and aspartate aminotransferase values are less than 5 times the normal.81 Liver biopsy may be occasionally recommended in AMA‐negative patients and to exclude other concomitant diseases such as AIH and nonalcoholic steatohepatitis, as discussed later in the Special Cases section. Role of Imaging Expert noninvasive imaging of the liver and biliary tree is mandatory in all patients with biochemical evidence of cholestasis. If the diagnosis is uncertain, then cholangiography may be necessary, preferentially with noninvasive magnetic resonance imaging or endoscopically, to exclude primary sclerosing cholangitis or other biliary tract diseases. Transient elastography80 is a noninvasive tool that has shown a high degree of accuracy in diagnosing advanced fibrosis in patients with PBC.92 Over a 5‐year period, on‐treatment liver stiffness appears stable in most noncirrhotic PBC patients, whereas it significantly increases in patients with cirrhosis. Progression of liver stiffness in PBC is predictive of poor outcome,80 and successful medical therapies have been associated with improvement in liver stiffness.94 The role of serial measurements as an endpoint is being evaluated, as is the value of magnetic resonance elastography. Diagnostic Approach The diagnosis of PBC is generally based on the presence of at least two of the following criteria: Biochemical evidence of cholestasis with elevation of ALP activity. Presence of AMA. Histopathologic evidence of nonsuppurative cholangitis and destruction of small or medium‐sized bile ducts if a biopsy is performed. The differential diagnosis includes a cholestatic drug reaction, biliary obstruction, sarcoidosis, AIH, and primary sclerosing cholangitis. Guidance Statements: Diagnosis The diagnosis of PBC can be established when two of the following three criteria are met: ▪ Biochemical evidence of cholestasis based on ALP elevation. ▪ Presence of AMA, or other PBC‐specific autoantibodies, including sp100 or gp210, if AMA is negative. ▪ Histologic evidence of nonsuppurative destructive cholangitis and destruction of interlobular bile ducts. Clinical Manifestations of PBC Symptoms The major symptoms of PBC are fatigue and itching. There is not a good correlation between these symptoms and stage of disease, although patients with more advanced disease generally have more symptoms. Fatigue Fatigue is the most common symptom in PBC; it has been found in 50% to 78% of patients and has a significant negative impact on quality of life.95 Severe fatigue may be associated with decreased overall survival.97 The etiology of the fatigue in PBC is unknown, but in some it may be associated with orthostatic hypotension, daytime sleepiness, cognitive defects, or impaired recovery of muscle from acidosis. 98 Fatigue from PBC is relatively constant or slowly progressive over time.99 Pruritus Early studies reported that pruritus (itching) occurs in 20% to 70% of patients with PBC. It is now less common because of the growing number of patients with PBC who are diagnosed in the early, asymptomatic phase.100 Patients report itching as local or diffuse and often exacerbated by contact with clothing, heat, or pregnancy. It has a circadian rhythm and is worse in the evenings. The clinical course of itching in PBC often fluctuates, with periods of relative exacerbation and improvement. Paradoxically, pruritus has been reported to wane in very advanced liver disease.101 The origin of pruritus in PBC is still unknown.103 However, several important mediators in the pathophysiology of cholestatic pruritus, which provide opportunities for therapeutic intervention, have been identified, including lysophosphatidic acid,105 endogenous opioids, and bile acids. Lysophosphatidic acid is a lipid‐signaling molecule that is elevated in many (but not all) cholestatic patients with itch. Lysophosphatidic acid injected into mice causes itch in a dose‐dependent manner. Activity of autotaxin, the enzyme that produces lysophosphatidic acid, correlates with itch intensity in PBC patients with pruritus.105Endogenous opioids are also increased in many patients with PBC pruritus (and some without pruritus).106 Opioids such as morphine and heroin commonly cause the side effect of pruritus, and cholestatic itch has been ameliorated by opiate antagonists.107 Some component of bile that accumulates in serum has long been suspected to contribute to pruritus. This is supported by the therapeutic efficacy of biliary drainage or plasma‐filtering procedures. The lack of correlation of serum bile acid levels with cholestatic itch suggests some other factor as the pruritogen. Abdominal Pain Right upper quadrant pain is found in approximately 17% of patients with PBC. It is typically nonspecific in character, not progressive in nature, not well correlated with disease stage or hepatomegaly, and often disappears spontaneously. Its etiology is unknown.108 Other Autoimmune Conditions There are three major autoimmune diseases that have been shown in a cohort study to occur significantly more often in PBC than the age‐matched and sex‐matched population: Sjögren syndrome; calcinosis, Raynaud, esophageal dysfunction, sclerodactyly, and telangectasias (CREST); scleroderma (systemic sclerosis); and Raynaud disease.109 Several reports suggest that patients with PBC have a greater risk of autoimmune thyroid disease; however, the latter is common in the general population. It is questionable whether celiac disease is more common in PBC. 110 Physical Examination The physical examination in early‐stage disease is usually normal, although hepatomegaly, excoriations, xanthelasma, and xanthoma may be seen. Jaundice is a late finding in patients with advanced liver disease. Increased melanin deposits causing hyperpigmentation are less common but may occur in later stages. Spider angiomata, edema, ascites, or splenomegaly may be found in the setting of portal hypertension. If limited scleroderma coexists, the examination may show sclerodoactyly or telangiectasias. Special Cases AMA‐Negative PBC The term AMA‐negative PBC refers to those who lack serum AMA but whose clinical presentation, liver histology, and natural history are nearly identical to patients with typical AMA‐positive PBC. The imprecise terms "autoimmune cholangiopathy" or "autoimmune cholangitis" should not be used interchangeably with AMA‐negative PBC. Given the specificity of antibodies to sp100, gp210, anti‐kelch‐like 12, and anti‐hexokinase 1 (when available), the diagnosis of AMA‐negative PBC requires a liver biopsy only in the absence of these PBC‐specific autoantibodies. Only true seronegative PBC requires a liver biopsy that should demonstrate the typical features of bile duct destruction seen in PBC—ideally a florid duct lesion and/or granulomas—in order to make a diagnosis of PBC. Although AMA‐negative PBC patients are nearly identical to AMA‐positive PBC patients, minor differences have been noted, including a higher prevalence of antinuclear and anti‐smooth muscle antibodies and lower serum IgM levels.111 Compared with AMA‐positive PBC patients, AMA‐negative PBC patients have more nonhepatic autoimmune conditions114 and worse health‐related quality of life in social and emotional domains.116 Histologically, AMA‐negative PBC has been shown to have greater bile duct damage and loss compared with AMA‐positive PBC.117 However, treatment response to UDCA appears similar in AMA‐negative and AMA‐positive PBC patients, and whether there are differences in clinical outcomes has not been resolved.113 Overlap of AIH with PBC There is no formal definition of the overlap syndrome between PBC and AIH. PBC/AIH overlap usually refers to simultaneous AIH in patients who have a diagnosis of AMA‐positive PBC and should not be used to refer to patients with AIH who have coincidental AMA. Conversely, "overlap" should not refer to PBC patients with serum antinuclear antibody and a mild degree of interface hepatitis because these are common features of PBC. Studies reported to date are of insufficient size to indicate with any degree of certainty how a diagnosis of PBC overlapping with AIH is different from uncomplicated PBC. Limited observational data suggest that biochemical response to therapy with UDCA for PBC/AIH overlap is no different from that observed in patients with PBC alone. A PBC/AIH overlap syndrome may also refer to patients with PBC followed sequentially by AIH or, less commonly, AIH followed by PBC.119