Algorithmic Approach to Diagnosis of Medical Liver Disorders

Chronic Hepatitis

Hepatitis is defined as an inflammatory process that leads to hepatocyte damage. Clinically, it manifests with elevated transaminases. Hepatitis is categorized as either acute or chronic, based on a variety of clinical and histological features outlined in the following sections. Chronic hepatitis indicates an inflammatory liver dysfunction that has been present for 6 months or more. It is characterized by portal mononuclear inflammation, usually in combination with a variable degree of interface and lobular hepatocyte damage. The most common causes of chronic hepatitis are hepatotropic viruses (such as hepatitis B, C, and E) in which the inflammation often extends beyond the portal tracts into adjacent periportal parenchyma and is associated with hepatocyte injury at the portal tracts/lobular interface, which is termed interface hepatitis. There may also be some degree of lobular inflammation associated with hepatocyte necrosis ( Fig. 43.3 ).

In chronic hepatitis, the bile ducts may show mild epithelial damage, but they are not the primary target of injury. Lymphoid aggregates and lymphoid follicles are characteristic features of hepatitis C; however, they are not specific for hepatitis C ( Fig. 43.4 ). In chronic viral hepatitis, necroinflammatory activity is typically present at low levels throughout the natural history of the disease. It may diminish in late stages, and there may occasionally be acute flares (particularly in hepatitis C). Fibrosis may develop with time, regardless of the amount of inflammation ( Fig. 43.5 ).

In chronic hepatitis B, ground-glass hepatocytes help confirm the diagnosis, as it indicates hepatitis B surface antigen (HBsAg) accumulation within the endoplasmic reticulum as a result of viral DNA integration into the host genome. However, ground-glass hepatocytes are not always easy to identify; their appearance is highly variable and dependent on both the quality and type of fixation, as well as staining. In addition, ground-glass hepatocytes are not specific to hepatitis B. They may also be seen in immunosuppressed individuals, especially those receiving multiple medications (see later). In hepatitis B infection, an immunostain for HBsAg helps confirm the diagnosis. It may be positive, even in cases without readily apparent ground-glass inclusions ( Fig. 43.6 ). Immunostain with AHBsAg or DNA quantification of HBV can help reveal hepatitis B infections, even if the serological results are negative for hepatitis B infection. For instance, latent infections can occur when viral serology is negative.

If the clinical and serological data confirm chronic viral hepatitis, then the biopsy should be graded and staged accordingly. There are several grading and staging schemes available, and each has advantages and disadvantages. When a particular grading or staging system is used, the name of the system (e.g., METAVIR, Ishak, Batts-Ludwig, modified Ishak) should be stated in the diagnostic report so the clinician is aware and it can be used appropriately for clinical patient management. This author’s personal preference is the Batts-Ludwig system because of its simplicity, reproducibility, and clinical relevance. ^,

Portal Inflammation Associated with Other Disease Processes

Although portal inflammation is usually present in chronic hepatitis, it may also occur in a wide variety of other liver diseases, such as acute hepatitis, chronic biliary diseases such as PBC (especially in its early stage), DILI, and certain metabolic diseases, among others. It can also occur in other systemic diseases that do not primarily affect the liver, such as celiac disease. The type of infiltrate, the pattern of involvement (portal predominant or mixed portal and lobular), and the presence or absence of associated findings (e.g., duct injury in chronic biliary diseases) help provide clues to the correct diagnosis. For instance, a prominent portal inflammatory infiltrate may be present in patients with A1AT disorder or Wilson’s disease. In the former, characteristic round eosinophilic globules within periportal hepatocytes help provide a clue to the diagnosis. These globules are periodic acid–Schiff (PAS) positive and resist digestion with diastase ( Fig. 43.7 ). However, globules may also represent an acute-phase reaction during concomitant chronic viral hepatitis. Wilson’s disease may also resemble chronic hepatitis and show prominent portal lymphocytes. Accompanying findings are relatively nonspecific and include mild steatosis, Mallory-Denk bodies in periportal hepatocytes, binucleated hepatocytes, and clear (glycogenated) nuclei. Demonstration of increased copper deposition in hepatocytes by copper quantification studies helps confirm the diagnosis of Wilson’s disease.

If the lymphoid infiltrate in portal tracts appears atypical, then the differential diagnosis includes hematopoietic malignancies such as leukemia, lymphoma, and post-transplantation lymphoproliferative disorder. For instance, in Hodgkin’s disease involving liver, there may be a mixed portal and/or lobular infiltrate. The presence of Reed-Sternberg cells, combined with immunophenotyping of the inflammatory infiltrate, helps reveal the malignant nature of the lesion ( Fig. 43.8 ). The infiltrate in Epstein-Barr virus (EBV) hepatitis also tends to appear somewhat atypical.

A predominantly eosinophilic portal infiltrate is not a common pattern of liver injury, but when it occurs, parasitic infection should be suspected. Of these, schistosomiasis targets the portal venous system. Larva migrans can cause eosinophilic abscesses.

Primary Biliary Cholangitis

PBC is associated with both chronic portal inflammation and active duct injury/destruction of small to medium-sized bile ducts. The pathognomonic feature of early-stage PBC is termed a florid duct lesion, which is defined as a dense portal lymphoplasmacytic inflammation that surrounds a damaged bile duct and characteristically contains a nonnecrotizing granuloma. However, the histological changes of PBC are often patchy. Therefore diagnostic bile duct destructive lesions may not always be present in biopsy specimens from patients with PBC. In later stages, PBC is associated with a bile ductular reaction that appears to represent a compensatory mechanism to allow for maintenance of bile flow through the hepatic biliary system. As the disease progresses, ductopenia and fibrosis eventually ensue ( Fig. 43.9 ).

Portal Inflammation and Duct Injury Associated with Other Disease Processes

Acute T-cell–mediated rejection represents a prototypical mixed portal inflammatory infiltrate that includes lymphocytes and eosinophils as well as scattered other types of inflammatory cells ( Fig. 43.10 ). This mixed infiltrate is associated with lymphocytic infiltration of bile ducts as well as duct epithelial injury, seen as cytoplasmic vacuolization with nuclear enlargement and overlapping. The findings may closely resemble PBC in native liver. In fact, a challenging differential diagnosis in posttransplant allograft liver biopsies is acute T-cell–mediated rejection versus recurrent PBC. In such cases, other associated findings of rejection such as portal or central vein endotheliitis helps distinguish the two.

DILI may also show portal inflammation with or without duct injury. As DILI is always a diagnosis of exclusion, it is important to histologically and clinically rule out other potential causes. Establishing a temporal relationship between the initiation of the drug or supplement in question and the elevation of liver enzymes (including disappearance of symptoms on withdrawal of the drug and reappearance on rechallenge) is essential in confirming a diagnosis of DILI.

Acute Hepatitis

Hepatitis is considered acute if the clinical, laboratory, or histological evidence of liver inflammation persists for less than 6 months. It is associated with disease ranging from subclinical to self-limited symptomatic to overt hepatic failure. The characteristic features of acute hepatitis are prominent lobular inflammation with associated disruption of the normal lobular sinusoidal architecture (i.e., lobular “disarray”), hepatocyte injury in the form of cytoplasmic swelling and clearing, as well as apoptosis or necrosis. Necrosis may be patchy, may involve some or all liver zones, or may be confluent ( Fig. 43.11 ). Most types of acute hepatitis are associated with lobular inflammation that is disproportionately high in comparison with portal tracts, but acute hepatitis is also usually accompanied by a variable degree of portal inflammation, which in some cases can be quite prominent. Similar to chronic hepatitis, acute hepatitis generally causes little to no injury to bile ducts.

The severity of acute hepatitis ranges from scattered apoptotic hepatocytes associated with patchy lobular inflammation to severe lobular inflammation associated with portal-to-portal or portal-to-central “bridging necrosis” and liver parenchymal collapse. The presence of bridging “necroinflammatory” activity is typical of both acute and AIH. If it is present in cases of chronic viral hepatitis, it should trigger an evaluation for other potentially important concomitant diseases (e.g., superinfection with another type of hepatotropic virus) or the presence of an immunodeficiency state ( Table 43.3 ).

The most common etiological agents of acute hepatitis include hepatotropic viruses (hepatitis A, B, C, D, and E viruses), nonhepatotropic viruses, drugs/supplements or toxins, as well as AIH [see later]. There is a considerable overlap in histological findings between viral and nonviral etiologies as well as between drug-induced hepatitis and AIH, and it is only by correlation with serological studies that a definite etiology may be confirmed. If viral and serological studies are negative, then DILI or other disorders such as Wilson’s disease are entities that should be considered. Ultimately, about 15% of acute hepatitis cases that lead to liver failure remain idiopathic.

Autoimmune Hepatitis

AIH is characterized by the presence of portal inflammation, interface hepatitis, and prominent lobular inflammation. Although plasma cells are characteristic of AIH, they are not always prominent, and this may be dependent on the phase of disease and the treatment status ( Fig. 43.12 ). Some cases show predominant lymphocytic inflammation but without prominent plasma cells. In addition, plasma cells may also be prominent in other conditions, such as hepatitis A or DILI, the latter either as an idiosyncratic drug reaction or as a primary form of drug-induced AIH that is seen with minocycline, nitrofurantoin, and several other drugs.

Most patients with AIH before treatment show a robust hepatitis with severe inflammatory activity. This is characterized by the presence of marked-interface and lobular hepatitis, hepatocyte loss, and confluent necrosis. The latter may be localized around the central veins or may show a central-portal or a portal-portal (bridging necrosis) pattern, or it may involve entire lobules (“total parenchymal collapse”) ( Fig. 43.13 ). When the areas of confluent necrosis extend to the portal tracts, a ductular reaction often becomes prominent as well.

Patients with AIH may have bouts of severe activity followed by long periods of inactivity. Fibrosis develops as a result of hepatocyte necrosis/apoptosis, thus progression to cirrhosis is usually swift compared with typical cases of chronic viral hepatitis. As a result, AIH may demonstrate any of the following features ^, : (1) cirrhosis with either little or no necroinflammatory activity ( burned out AIH ); (2) intermediate-stage disease associated with moderate to severe activity, often combined with some degree of scarring and nodularity; or (3) early-stage disease associated with marked activity (at least focal confluent necrosis) as well as parenchymal collapse ( Fig. 43.14 ). However, patients with AIH are unlikely to show periods of mild activity combined with either mild or absent fibrosis. Thus biopsies that reveal both mild activity and mild fibrosis are unlikely to represent AIH. In such cases, viral hepatitis or DILI should be considered.

In AIH, the bile ducts may be obscured by the marked degree of portal inflammation, but they do not normally reveal significant lymphocytic inflammation or epithelial damage. If the portal inflammation also shows duct centricity and is associated with moderate or marked epithelial damage, then the possibility of an overlap syndrome with PBC should be considered (see later). In posttransplant allograft biopsies, the presence of a plasma-cell–rich hepatitis is either indicative of recurrent AIH or allograft rejection (i.e., plasma-cell–rich rejection). ^,

Primary Biliary Cholangitis–Autoimmune Hepatitis Overlap Syndrome

One frequently encountered problem is identification of a PBC-AIH overlap syndrome versus PBC or AIH alone. Similar to AIH, PBC cases may also show abundant plasma cells as well as mild interface and lobular hepatitis. If there are only scattered foci of interface and lobular hepatitis (similar to what one might see in hepatitis C), then the case likely represents only PBC. However, if there is confluent necrosis or widespread interface and lobular hepatitis that is easily recognizable at low magnification, then an overlap syndrome may be considered. This may be suggested on biopsy findings; however, it is ultimately confirmed clinically by showing proof of both serological and biochemical features of PBC and AIH, that is, positive antinuclear antibodies (ANAs) or anti–smooth muscle antibodies (SMAs), markedly elevated transaminases, and elevated alkaline phosphatase. Similarly, AIH alone may show mild bile duct injury or that the duct may be obscured by the brisk inflammation that is present in the portal tract. However, the duct injury would be proportionally mild compared with the amount of interface and lobular hepatitis, and the characteristic conspicuous inflammatory and destructive duct lesion (i.e., florid duct lesion) of PBC will not be present in AIH alone.

Wilson’s Disease

As mentioned earlier, Wilson’s disease can have different presentations with different histological patterns of injury. The chronic form resembles chronic hepatitis with variable interface and lobular hepatitis and variable fibrosis, as described earlier. However, Wilson’s disease may also present acutely with a histological pattern of acute hepatitis including severe hepatitis with bridging necrosis. This form may be the first clinical presentation of the disease. In such cases, accompanying laboratory/clinical features and quantitative copper assay on biopsy are helpful in distinguishing the Wilson’s form from other forms of acute hepatitis.

Nonhepatotropic Viral Hepatitis

Although most nonhepatotropic viruses (e.g., cytomegalovirus [CMV], herpes simplex virus [HSV], and adenovirus) can cause hepatitis, these organisms are not generally associated with prominent portal or lobular inflammation. HSV and adenovirus hepatitis characteristically show significant hepatocellular necrosis (see later). EBV infection, on the other hand, may be associated with significant inflammatory infiltrate. Hepatic involvement with EBV infection is common but is often subclinical and self-limited. EBV-related hepatitis occurs predominantly in immunocompromised patients and rarely in immunocompetent patients. The characteristic histological findings include a diffuse lymphocytic sinusoidal infiltrate in a “string of beads” pattern, with or without associated apoptotic bodies, as well as expansion of portal tracts by a predominantly lymphocytic infiltrate. The lobular architecture is generally intact. The portal mononuclear infiltration may be to such a degree that it mimics chronic hepatitis B or C in some instances. The infiltrating lymphocytes may appear larger and slightly more atypical than mature lymphocytes. The diagnosis can be confirmed with in situ hybridization for EBV-encoded RNA (EBER) ( Fig. 43.16 ). ^,

CMV hepatitis occurs almost exclusively in immunocompromised patients, such as those who have had a bone marrow transplant. Characteristic features include the presence of CMV inclusions, which are eosinophilic inclusions located in both the cytoplasm and nuclei of affected cells. CMV may infect hepatocytes, cholangiocytes, or endothelial cells. CMV-infected cells may be present randomly throughout the lobule, without any particular preferential zone of involvement. Some cases are associated with neutrophilic microabscesses within the liver parenchyma ( Fig. 43.17 ). However, neutrophilic microabscesses are neither a sensitive nor specific finding in CMV hepatitis. CMV hepatitis may also be associated with portal and lobular inflammation, and it may show overlapping features with acute T-cell–mediated rejection in posttransplant cases. Immunostains for CMV help confirm the diagnosis.

Resolving Acute Hepatitis

As mentioned earlier, many types of acute hepatitis resolve. During the resolving period, the inflammation and necrosis subside, and phagocytic activity predominates. If a liver biopsy is taken during this period, it often shows clusters of pigment-laden Kupffer cells, which are silvery-gray on hematoxylin and eosin (H&E) stain but bright magenta with PAS stain after diastase digestion (PASD) ( Fig. 43.18 ). Kupffer cells represent the tissue repair associated with prior hepatocyte injury, such as from acute viral hepatitis, toxins, medications, or dietary supplements, and they may be located in the portal tracts or in the lobules. Mild portal and lobular inflammation may also still be present. Other representative tissue responses that help provide evidence of a prior and currently resolving liver injury include hepatocellular regeneration (e.g., increased binucleation, slightly thickened plates) and anisonucleosis. These patients do not typically progress to chronic liver disease or even suffer from recurrences. One appropriate diagnostic statement for such cases is “features of resolving hepatitis/prior parenchymal injury.”