—  SHORT COURSE  —

Disorders of the Intra- and Extrahepatic Bile Ducts

Case 1 - Primary Biliary Cirrhosis, Stage 2 (Periportal Stage)

Kay Washington, M.D., Ph.D.
Pathology, C-3321 MCN
Vanderbilt University Medical Center
Nashville, TN 37232-2561


Clinical History
This 50 year old woman had an 8 year history of pruritis, elevated alkaline phosphatase levels, and a positive serologic test for anti-mitochondrial antibodies. The patient had esophageal varices but had not suffered any episodes of bleeding. She developed debilitating fatigue and underwent orthotopic liver transplantation.

Morphologic Features
The native liver was normal to slightly enlarged, with a subtle nodularity on sectioning, without increased firmness. The extrahepatic bile duct was normal. On microscopic examination, the portal tracts contain an increased number of mononuclear inflammatory cells, with minimal piecemeal necrosis or interface hepatitis. The inflammatory infiltrate is composed predominantly of small lymphocytes, with a sprinkling of eosinophils and plasma cells, and is centered about bile ducts. Both medium-sized and small interlobular bile ducts are affected. In some areas, a granulomatous component surrounds an injured bile duct and the duct epithelium shows degenerative changes such as pyknosis and cytoplasmic vacuolization. Interlobular bile ducts are lost from some portal tracts, and there is slight bile ductular proliferation. The portal tracts are slightly expanded by fibrous tissue, without bridging. Minimal inflammation is seen in the lobules, and no canalicular or chronic cholestasis is seen.

Click on each slide thumbnail image for an enlarged view:

Slide 1
Primary Biliary Cirrhosis
A damaged medium-sized interlobular bile duct is surrounded by a dense mononuclear inflammatory infiltrate. Lymphocytes focally infiltrate bile duct epithelium.
Slide 2
Primary Biliary Cirrhosis, Florid Duct Lesion
Granulomatous destruction of bile ducts is a characteristic histologic hallmark of primary biliary cirrhosis, although granulomas are not seen in all cases and may be absent in late stages. Epithelioid macrophages may be loosely grouped in ill defined clusters or may form a sarcoid-like granuloma, as shown here.
Slide 3
Primary Biliary Cirrhosis, Florid Duct Lesion
The bile duct epithelium shows degenerative changes such as vacuolization and cytoplasmic granularity.


Diagnosis: Primary Biliary Cirrhosis, Stage 2 (Periportal Stage)

Clinical Features
In primary biliary cirrhosis, the intrahepatic bile ducts are progressively destroyed by a non-suppurative inflammatory process. The disease has distinctive clinical features, being found primarily in women (90% of patients), mostly in the fifth to seventh decades. PBC is probably autoimmune in etiology, judging by its association with other autoimmune disorders such as Sjogren's disease and keratoconjuctivitis sicca, and may in some patients represent a generalized disorder of lacrimal, salivary, and pancreaticobiliary small duct epithelia. Large intra- and extrahepatic bile ducts are not affected. The most specific feature of PBC is the presence of antimitochondrial antibodies in the serum of 90% of patients affected. Antibodies directed to the PDC-E2 antigen, a component of the pyruvate dehydrogenase enzyme complex present on the inner mitochondrial membrane, are highly specific (96%) for PBC. Immunohistochemical staining shows that expression of either PDC-E2 or a PDC-E2 mimic is increased in bile duct epithelial cells of PBC patients, and aberrant luminal expression is seen. Recent reports suggest that the epitope recognized by antibodies producing apical staining in biliary cells in primary biliary cirrhosis is the inner lipoyl domain of PDC-E2 (1) . The exact mechanism by which AMA might be cytopathic to biliary epithelial cells remains to be elucidated, however. The presence of serum AMA indicates a specific B-cell response to this mitochondrial antigen; specific T cell responses are seen as well (2) . Other circulating autoantibodies such as anti-smooth muscle and anti- nuclear antibodies and rheumatoid factor are often present. Hypergammaglobulinemia with a selective elevation of IgM is often seen. An infectious etiology has been postulated (2)  , with recent reports of cloning of a retroviral sequence directly from biliary epithelium from PBC liver (3) . Genomic analysis of differentially expressed gene s in bile duct cells from PBC livers shows upregulation of genes in involved in signaling, mitochondrial function, inflammation, and fibrosis (4) .

Most patients with PBC present with fatigue (21%) and pruritis (19%) (5) , the latter due to the accumulation of bile salts. Many asymptomatic patients are now identified after screening tests show elevation of serum alkaline phosphatase. Patients are rarely jaundiced early in the course of the disease; indeed, the presence of bile pigment in a liver biopsy suspected of harboring low-stage PBC should prompt a reconsideration of the diagnosis. PBC follows a progressive clinical course in most patients, and most but not all asymptomatic patients will develop significant liver disease.

Survival is variable, but is generally from 6 to 12 years after presentation for symptomatic patients. In one recent study, 26% developed liver failure by 10 years after diagnosis (5) . Ursodeoxycholic acid is used for treatment in early stages; liver transplantation is the only effective therapy for late stage disease.

Pathology
The characteristic lesion of primary biliary cirrhosis is the so-called florid duct lesion, sometimes also called chronic nonsuppurative destructive cholangitis (6) . Interlobular bile ducts 40 to 80 microns in diameter are typically involved. In early stage PBC, the diagnostic lesions may be focal and may not be sampled on needle biopsy. The three components of the florid duct lesion are inflammation, injury to bile duct epithelial cells, and disruption of the bile duct basement membrane. The inflammatory infiltrate is composed of lymphocytes, scattered eosinophils, macrophages, and a variable number of plasma cells, and is intimately associated with the bile duct. The macrophages may be dispersed throughout the portal inflammatory infiltrate or may be aggregated into loose clusters or occasionally into well-formed granulomas. Granulomas and Kupffer cell aggregates may be present in the lobule. In early stages, the inflammatory infiltrate is largely confined to the portal tract. The biliary epithelial cells of injured bile ducts are swollen, and focally stratified, and may be vacuolated. Lymphocytes commonly infiltrate bile duct epithelium. The basement membrane becomes disrupted and fragmented, best visualized on PAS stain. Lytic necrosis, not apoptosis, appears to account for most of the biliary epithelial loss (7) . In small portal tracts, bile ducts are often absent and seem to have vanished without a trace, although aggregates of lymphocytes or PAS-positive basement membrane material may mark their former location. Canalicular cholestasis is not a feature of early stage PBC.

As the duct destruction progresses, bile ductular proliferation accompanied by fibrosis develops at the periphery of portal triads, and portal tracts enlarge by this process of biliary piecemeal necrosis. In some cases the inflammatory infiltrate spills over into the adjacent parenchyma, and lymphocytic piecemeal necrosis may mimic chronic hepatitis. At this stage the changes of chronic cholestasis begin to appear, with swollen and rarefied periportal hepatocytes and accumulation of copper. As periportal fibrosis progresses, portal-portal fibrous bridges are formed. Bile ductular proliferation often subsides in late stage PBC, and in the cirrhotic stage little ductular or ductal epithelium can be identified. The cirrhosis has a typical biliary pattern, in which the nodules have an irregularly shaped "jigsaw puzzle piece" profile.



Histologic Differential Diagnosis
The term "AMA-negative PBC" or " autoimmune cholangitis" has been applied to cases that are clinically, histologically, and biochemically compatible with PBC except for the lack of identifiable antimitochondrial antibodies. More sensitive testing using cloned mitochondrial antigens such as a triple hybrid recombinant molecule may identify AMA in some patients previously thought to be seronegative (2) . In retrospective studies, no significant differences between patients with PBC and these AMA-negative patients have been described (8-12) . However, a recent prospective study describing 20 patients with autoimmune cholangitis reports that these patients have higher serum levels of AST and bilirubin and lower serum IgM than patients with classic PBC (13) . Antibodies to carbonic anhydrase are present in the serum of patients with autoimmune cholangitis in some studies, but have not been discriminatory in others. Of the 15 patients with autoimmune cholangitis with biopsies reported in one study, six had a PBC-like and 7 had a PSC-like pattern of injury, suggesting that "autoimmune cholangitis" may represent a mixed group of autoimmune disorders at varying stages, or possibly a transition state (13) . AMA-negative patients were slightly younger in one group (50 vs. 55 years) but were otherwise indistinguishable (8) . Although data are largely lacking, it is though that the response to ursodeoxycholic acid (UDCA) therapy in these patients is the same as for those who are AMA-positive, and there are accordingly no differences in the treatments prescribed for these two groups at the present time.

The differential diagnosis for PBC depends on the stage of the disease. In stage 1 and 2 disease, portal inflammation, piecemeal necrosis and bile ductular proliferation may mimic chronic hepatitis, particularly hepatitis C. Bile duct damage is less prominent in chronic hepatitis and bile duct loss is rarely seen, but lymphocytic infiltration of bile duct epithelium is often a feature of hepatitis C. A recent study using immunostaining for cytokeratin 7 reports that absence of central interlobular bile ducts and lack of a lumen in preserved ducts, presumably due to cell swelling, are features of primary biliary cirrhosis but not chronic hepatitis (14) . Clinical information such as antimitochondrial antibody status and serologic markers for viral hepatitis is helpful in most cases.

It may be more difficult to distinguish autoimmune hepatitis from PBC, however, and indeed this distinction may prove impossible on histologic grounds. Because treatment for autoimmune hepatitis differs from that for primary biliary cirrhosis, accurate diagnosis is important. Difficulties arise because the portal inflammatory infiltrate of PBC often contains numerous plasma cells, and infiltration of bile duct epithelium by lymphocytes is not uncommon in autoimmune hepatitis, if looked for, and some degree of bile duct injury is often present. Although non-destructive bile duct lesions are quite common in autoimmune hepatitis, duct loss is generally not a feature, and granulomatous bile duct destruction is not seen. Serum alkaline phosphatase, cholesterol, and IgM levels are elevated to higher levels in PBC. To add to the problem, some patients with clinical and histologic features of autoimmune hepatitis will have serum anti-mitochondrial antibodies. In some cases this is caused by misreading of immunofluorescence-type tests (confusing anti-LKM antibodies with antimitochondrial antibodies). In other patients, however, the AMA is truly positive, but usually in low titer. Serologic markers may not be definitive in such cases, as patients with PBC may have a positive ANA and patients with autoimmune hepatitis may have a low titer AMA. The term "overlap syndrome" is used for cases of autoimmune liver disease with both cholestatic and hepatitic features that do not fit readily into the usual diagnostic categories (15,16) . Liver biopsies in such cases show features of both PBC (granulomatous inflammation and bile duct lesions) and autoimmune hepatitis (piecemeal necrosis and spotty hepatocyte necrosis) (17) . In addition to these cases with "overlapping" simultaneous features of both diseases, rare patients who switch from one disease to another over time are reported (18) .

The existence of this overlap syndrome between PBC and autoimmune hepatitis is generally recognized, although investigators disagree over exact classification. Some researchers (15)  consider these patients to have PBC, based on duct destruction and presence of AMA, and have proposed that these cases be classified as "PBC, hepatitic form". Others have concluded that overlap of PBC and autoimmune hepatitis is not rare, and that combination therapy with ursodeoxycholic acid (UDCA) and steroids is indicated in most of these patients to obtain a biochemical response (16) . In this recent study of 12 such patients, the authors found that "overlap " cases constituted 9% of 130 consecutive patients with a diagnosis of PBC. Because of the observation that some patients diagnosed with PBC have a flare of hepatitic activity when treated with ursodeoxycholic acid, it has been proposed that response to UDCA may unmask the hepatitis component in overlap patients (16) . Further complicating the issue, some investigators suggest that features of AIH in PBC may be transient (19) .

On a practical note, what does the surgical pathologist need to know about overlap syndrome? Exact classification of these patients may change as we learn more about the pathophysiology of these diseases. The term "overlap syndrome" should not be overused by applying it to otherwise typical cases of PBC with prominent interface hepatitis. In general, in low-titer AMA-positive patients, if the liver biopsy shows features typical of autoimmune hepatitis, such as prominent piecemeal necrosis, numerous plasma cells in the inflammatory infiltrate, and lobular hepatitis, without prominent bile duct destruction, and liver tests favor a hepatitic process over chronic cholestasis, clinicians will often consider this patient to have autoimmune hepatitis and prescribe immunosuppressive therapy such as corticosteroids. Since UDCA has few side effects, it may be used as well. True overlap syndromes do occur but are fairly rare, constituting less than 10% of PBC patients (16) , and most patients with clinical or histologic features that strongly suggest a component of autoimmune hepatitis will be treated with a course of immunosuppression.



Distinction of PBC from those cases of sarcoidosis with destruction of bile ducts by granulomas may be difficult (20,21) . In a study of 100 cases of hepatic sarcoidosis, 58% of the biopsies showed evidence of cholestasis, generally feathery degeneration and increased copper storage (20) . Nineteen of these biopsies had bile duct lesions similar to those seen in PBC. The granulomas of sarcoidosis tended to be better formed and more numerous than those of PBC. The lack of AMA positivity and the presence of pulmonary involvement also favor a diagnosis of hepatic sarcoidosis. Of note, sarcoidosis may also cause intrahepatic biliary strictures that have cholangiographic features resembling primary sclerosing cholangitis (22) .

The Surgical Pathology Report in PBC
The following features may be useful to note in the surgical pathology report in primary biliary cirrhosis:

  • Description of bile duct lesion: granulomatous, lymphocytic, loss of bile ducts
  • Nature of portal inflammatory infiltrate: are plasma cells prominent?
  • Presence of piecemeal necrosis or interface hepatitis
  • Bile ductular proliferation
  • Lobular activity: lymphocytes, granulomas, Kupffer cell aggregates, hepatocyte injury
  • Cholestasis: canalicular bile plugs (rare), feathery degeneration, Mallory's hyaline (late stage)
  • Extent of fibrosis (stage)


Histologic Staging of Primary Biliary Cirrhosis
The value of histologic staging in assessing prognosis in PBC is debatable, given the lack of uniformity of duct loss and fibrosis in the liver in this disease. However, the presence of portal-portal bridging fibrosis on biopsy has been shown to be a poor prognostic sign. Several staging schemes have been described, and there is little practical difference between the two that are most commonly employed, those described by Scheuer (23)  and Ludwig (24) . In stage 1 disease, damage to interlobular bile ducts is seen in the form of the florid duct lesion. In stage 2, the effects of duct injury result in extension of the process to involve the periportal areas, and ductular proliferation, probably representing a compensatory reaction to bile duct loss, is prominent. Stage 3 is characterized as a scarring or precirrhotic stage, with bridging fibrosis. Stage 4 is cirrhosis.



Comparison of Histologic Features of PBC, PSC, Chronic Hepatitis, and Sarcoidosis
Feature PBC PSC Chronic hepatitis Sarcoidosis
Chronic cholestasis prominent, late prominent, late trace, late variable
Copper storage variable variable trace variable
Duct loss extensive extensive rare variable
Granulomas variable rare rare key feature
Interface hepatitis variable variable key feature absent

References

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