Chronic Viral Hepatitis

As in acute hepatitis, patients with chronic hepatitis have a wide spectrum of clinical manifestations that range from asymptomatic to symptomatic decompensated cirrhosis. Many patients are asymptomatic or have only mild, nonspecific complaints, such as fatigue. Findings on physical examination are typically few but include hepatomegaly and other stigmata of chronic liver disease, such as palmar erythema. Ascites and esophageal or cutaneous varices may also develop in patients with advanced cirrhosis. Serum aminotransferase levels fluctuate but are usually chronically elevated in the 2- to 10-fold range, although a substantial number of patients with mild chronic hepatitis C have persistently normal aminotransferase levels. Alkaline phosphatase and bilirubin levels are usually normal to mildly elevated unless hepatic decompensation has occurred, in which case high levels may be observed.

Hepatitis B

HBV contains a partially double-stranded, circular DNA genome and is a member of the hepadnavirus family of viruses. The complete viral particle, referred to as the Dane particle, consists of an outer envelope that surrounds a core of DNA, the hepatitis B core antigen (HBcAg), the hepatitis B e antigen (HBeAg), and DNA-dependent polymerase. The outer envelope contains the hepatitis B surface antigen (HBsAg). Both complete and incomplete viral particles circulate in the blood of infected patients. In fact, HBsAg can circulate in large quantities as incomplete tubular or spherical structures that lack DNA. Viral DNA may become incorporated into host DNA within infected hepatocytes, particularly in young patients, and these patients are at high risk for subsequent development of hepatocellular carcinoma. The viral antigen load and subsequent antibody response may be used as serologic markers to evaluate the time course of infection (Table 46.2).

HBV is transmitted through exposure to infected body fluids and by intravenous drug use, sexual contact, and occupational activity. Perinatal transmission is common (90%) if the mother is HBeAg positive, which is indicative of highly infectious disease and active viral replication, but less common (10%) if the mother is HBsAg positive. In high-prevalence areas, HBV infection is often acquired by maternal–neonatal transmission, which results in a high rate of chronic disease. In areas of low prevalence, hepatitis B is mainly a disease of young adults, who acquire the virus through parenteral or sexual exposure. Posttransfusion hepatitis B is virtually nonexistent in the United States because of routine screening of blood donors.

HBV is responsible for as many as 40% of cases of acute hepatitis in the United States. Clinical symptoms of acute hepatitis develop in approximately 30% of infected adults but in only 10% of children younger than 4 years of age; they typically appear 45 to 180 days after exposure.⁵ Fulminant hepatic failure occurs in approximately 1% of cases of acute hepatitis B. Acute liver failure may also occur in patients with chronic hepatitis B in which mutations are present in the precore, or core promoter, regions of the viral DNA.⁵ Chronic hepatitis develops in fewer than 10% of adult patients but in as many as 90% of infected infants. The rate of progression to cirrhosis depends on the presence or absence of active viral replication and the severity of liver damage (evident histologically). For instance, 50% of patients with chronic hepatitis B and marked activity progress to cirrhosis within 4 years. The annual probability that cirrhosis will develop is estimated to be 12% for patients with chronic hepatitis B. Hepatocellular carcinoma develops in 2.4% of patients with chronic hepatitis B annually, as well as in 0.5% of patients with chronic hepatitis without cirrhosis.⁵

Hepatitis C

HCV is a spherical, enveloped, single-stranded RNA virus that measures approximately 50 mm in diameter. It is classified as a separate genus within the Flaviviridae family. The genome for HCV is characterized by sequence heterogeneity, which is a result of pressure from the host immune system. This feature allows the virus to escape immune surveillance and establish chronic infection. Six major genotypes are recognized: the most common are 1a, 1b, 2a, and 2b.

HCV is transmitted primarily by parenteral exposure. Intravenous drug users and patients with hemophilia have a particularly high prevalence rate of infection. Intranasal cocaine use and sexual promiscuity are independent risk factors for acquisition of infection,⁶ although the risk associated with sexual transmission of HCV is low compared with the human immunodeficiency virus (HIV) or HBV.⁷ Although this virus was initially identified as the etiologic agent of transfusion-acquired “non-A, non-B” hepatitis, posttransfusion hepatitis C has decreased dramatically because of widespread implementation of donor screening. The risk of infection with HCV is now estimated to be 0.01% to 0.001% for each unit of blood transfused.⁷ Rates of perinatal transmission are estimated to be lower than 5%.

HCV accounts for approximately 15% of cases of acute hepatitis in the United States,² but acute infection is usually asymptomatic and only rarely recognized clinically. The incidence of acute HCV infection peaked in the late 1980s and early 1990s and has been steadily declining since, to less than 20 acute infections per 100,000 individuals per year .⁸ The incubation period of hepatitis C is 7 weeks, with a range of 2 to 30 weeks based on studies of transfusion-acquired cases.⁹ Fulminant hepatitis C is rare. Chronic infection is a far more common problem, occurring in at least 85% of infected patients. Most patients with chronic hepatitis C have few or no symptoms. Serum aminotransferase levels are often only mildly elevated, fluctuating from 1.5 to 10 times the upper limit of normal, and as many as 30% of patients have normal aminotransferase levels.¹⁰ Factors associated with progressive disease include patient age older than 40 years at the time of exposure, immunodeficiency, a high degree of viral heterogeneity, genotype 1, male gender, and long duration of infection.^8,10 Alcohol is known to potentiate viral replication and is associated with greater activity and fibrosis.¹¹ Although hepatic steatosis has been correlated with increased progression of fibrosis, it is unclear whether this result is confounded by associated metabolic abnormalities.⁸ Diagnostic tests currently in use include polymerase chain reaction (PCR) for detection of circulating viral RNA and a third-generation enzyme immunoassay for detection of anti-HCV antibodies.

The natural history of HCV infection has proved challenging to study, in part because of the difficulty in determining onset of infection. In most patients, the disease is believed to have an indolent course for as long as 2 decades; cirrhosis has developed in 20% to 40% of patients in studies with at least 10 to 20 years of follow-up.^8,12 Currently, chronic hepatitis C is the reason for 30% of liver transplantations performed in the United States. The risk of hepatocellular carcinoma in HCV-related cirrhosis is estimated to be approximately 1% to 4% per year.¹⁰

Occult HCV infection is a more recently recognized entity that has two distinct types of clinical presentation. The first type occurs in patients with persistently elevated liver function test results but negative serologic test results for HCV.^13,14 The second type is seen in patients with positive anti-HCV serology, absence of serum HCV-RNA, and normal liver function test results. In an initial study of 100 patients with elevated liver function test results and negative HCV serology, more than half were found to have HCV-RNA in their livers by reverse transcriptase (RT)-PCR and in situ hybridization.¹⁴ Preliminary studies have demonstrated that patients with occult HCV infection have higher triglyceride and cholesterol levels, decreased necroinflammatory scores and fibrosis, and fewer HCV-infected hepatocytes (by in situ hybridization).^13,15

Patients with hepatitis C may also be coinfected with HIV, especially high-risk individuals such as intravenous drug users. As many as 25% of HIV-infected individuals in North America are also infected with HCV.^16,17 Effective use of highly active antiretroviral therapy (HAART) has decreased the morbidity and mortality rates from HIV infection and increased the risk of death from other causes, such as hepatitis C liver disease.

HCV infection is associated with a variety of extrahepatic manifestations and is now thought to be responsible for most cases of essential mixed cryoglobulinemia.¹⁸ HCV is also strongly associated with porphyria cutanea tarda (PCT) in the United States, although there is marked geographic variation in the prevalence rate of HCV in patients with PCT.¹⁹ Homozygosity for the Cys282Tyr mutation in the hemochromatosis gene and HCV infection are significant risk factors for the expression of PCT, with heavy alcohol use often being a contributing factor.²⁰ The characteristic birefringent, yellow-brown, needle-shaped crystals described in PCT are rarely found in routinely processed liver biopsy specimens because they are highly soluble in water.

Hepatitis D

HDV, also known as the delta agent, is a small, defective RNA virus that requires HBsAg for packaging and transmission to cause infection and tissue injury. It is spread by mechanisms similar to those that transmit HBV, and it may manifest as a coinfection or superinfection with HBV. HDV infection can cause acute or chronic hepatitis. Coinfection or superinfection can cause fulminant hepatic failure. HDV infection should be suspected in all patients with hepatitis B in whom severe exacerbation of disease activity develops. The finding of anti-HDV antibody in a patient who is seropositive for HBsAg is diagnostic. Three genotypes are recognized.²¹ In general, the histologic features of HDV infection are not distinctive, but HDV is associated with more pronounced necroinflammatory activity and more rapid progression than is seen in patients with isolated HBV infection. Microvesicular fat may be present in severe cases.²² Delta antigen can be demonstrated by immunohistochemical means and is located primarily in hepatocyte nuclei.²²

Hepatitis E

HEV is a small, nonenveloped, single-stranded RNA virus that was originally classified in the family Caliciviridae but subsequently placed in the family Hepeviridae.²³ Hepatitis E is endemic in parts of Africa, India, southeast and central Asia, and Mexico. Fecal-oral transmission usually occurs through ingestion of contaminated water, although sporadic cases associated with animal contact or consumption have been documented.²³ HEV causes a mild form of acute hepatitis, which lasts 1 to 4 weeks in most patients but is particularly severe in pregnant women, in whom it is associated with an increased risk of acute liver failure and a mortality rate of as much as 25%. The incubation period is 4 to 5 weeks. Reports of histopathology indicate multiple patterns, ranging from a typical acute hepatitis morphologic picture, to a cholestatic form with canalicular bile plugs and cholestatic pseudorosettes, and, in a small series of patients with autochthonous infection, a severe form showing mixed portal and acinar inflammation with severe interface hepatitis and cholangiolitis.²⁵ Massive or submassive necrosis may occur in severe cases. Although HEV infection has been considered a self-limited disease, persistent infection has been documented in immunocompromised patients and in patients with HIV infection.²⁶ Serologic assays for anti-HEV IgG and IgM, and RT-PCR assay are used to confirm the clinical diagnosis.²⁴

Other Hepatitis Viruses

GB virus type C (GBV-C), also known as the hepatitis G virus, was discovered in 1995 and is a flavivirus in the same family as HCV. This virus has been detected in 1.7% of the population and can be transmitted parenterally and by vertical transmission.²⁷ Viral replication occurs predominantly in lymphocytes, although the virus is also detectable in hepatocytes.

The single-stranded, nonenveloped DNA virus known as TT virus was originally suspected to cause transfusion-associated hepatitis, but later it was found in more than 90% of Japanese blood donors, casting doubt on its role in causing disease.²⁸ Similarly, the related single-stranded circular DNA virus, the SEN virus, has also been found in patients with transfusion-associated hepatitis, although direct causality has not been established.²⁹

Massive and Submassive Necrosis

In severe cases of acute viral hepatitis, portions of the hepatocyte lobules (submassive necrosis) or entire contiguous lobules (massive necrosis) may undergo necrosis. Submassive necrosis usually involves zone 3 hepatocytes initially but may extend to zone 2 regions with progression. Extensive destruction of hepatic parenchyma results in the clinical syndrome of fulminant hepatic failure. On gross examination, livers with massive necrosis appear shrunken and flaccid, often showing wrinkling of the capsular surface and a mottled appearance of the liver parenchyma. Regenerating nodules of hepatocytes, which are often bile stained, may be irregularly distributed in the liver and may form nodular masses. The degree of necroinflammatory activity is variable, even among patients with a similar clinical course.³⁰ In fulminant cases, one often sees a prominent bile ductular reaction, with associated neutrophils (cholangiolitis), typically located in the peripheral region of the portal tracts (Fig. 46.5). However, the histologic features of submassive or massive hepatic necrosis are not specific for acute viral hepatitis. This pattern of injury can develop as a result of toxic injury, severe drug reaction, or Wilson disease, among other causes. A trichrome stain to highlight connective tissue is useful to distinguish massive hepatic necrosis from cirrhosis by demonstrating the lack of dense collagen deposition in the former. A reticulin stain is also helpful to demonstrate the presence of a collapsed reticulin framework.

Prognostic Factors

Pathologic features of acute viral hepatitis that are predictive of progression to chronicity are difficult to elucidate, in part because of the rarity of liver biopsies from patients with acute hepatitis. Furthermore, in patients with massive hepatic necrosis, an individual liver biopsy may not represent the overall status of the liver, because hepatocyte regeneration and necrosis can vary substantially from region to region.

Differential Diagnosis

Several major entities may be confused with acute viral hepatitis—in particular, chronic viral hepatitis, autoimmune hepatitis, and drug-induced hepatitis (Table 46.4). In cases in which the lobular inflammatory component is prominent, a markedly active chronic hepatitis may be confused with acute hepatitis. Some patients with autoimmune hepatitis exhibit an “acute” clinical picture and have a prominent lobular inflammatory infiltrate with extensive necrosis that may be difficult to distinguish from acute viral hepatitis. However, autoimmune hepatitis often reveals prominent plasma cell infiltrates (particularly in the portal tracts), marked periportal inflammation and necrosis, and mild bile duct injury. Also, in autoimmune hepatitis, fibrosis often exists at the time of presentation, even with an acute clinical picture. Serologic tests for autoimmune markers are usually helpful. Viral hepatitis also can be confirmed or excluded based on serologic or PCR-based testing, but some autoimmune markers, such as antinuclear antibody, are not always positive early in the course of autoimmune hepatitis.

Drug-induced hepatitis can be indistinguishable from acute viral hepatitis (see Chapter 48 for more detail). The presence of prominent eosinophils, granulomas, sinusoidal dilation, prominent bile ductular reaction, cholestasis, and fatty change may suggest a drug reaction, but these are not considered pathognomonic features. One helpful hint is that acute or chronic forms of hepatitis that do not seem to fit into a discrete morphologic category, or that show overlapping features such as cholestasis and lobular hepatitis, may represent a drug reaction. Obtaining a complete history of drug and toxin exposures is critical to disting repeated drug reactions from viral hepatitis. Furthermore, superimposed drug injury may develop in patients with acute viral hepatitis, so the two entities are not necessarily mutually exclusive. Kupffer cell aggregates are common in resolving acute viral hepatitis and should not be mistaken for non-necrotizing granulomas.

Portal Inflammation

Chronic hepatitis is characterized by the presence of inflammatory infiltrates that involve the portal tracts, which may range from mild and patchy to prominent and diffuse. The infiltrates consist primarily of lymphocytes, often with a variable number of plasma cells. Scattered macrophages, neutrophils, and eosinophils may be found in some cases but are typically a minor component of the infiltrate in chronic viral hepatitis. Lymphoid follicles may be present, particularly in hepatitis C, and germinal centers may also be seen (Fig. 46.6). A bile ductular reaction may be seen at the periphery of portal tracts, but this feature is not specific and usually is not very prominent in viral hepatitis. As with any type of bile ductular reaction, neutrophils are usually associated with the proliferating ductular epithelium as a result of cytokines released by biliary epithelium, and this should not be interpreted as evidence of biliary obstruction or acute cholangitis.

Interface hepatitis, also known as “interface activity” or “piecemeal necrosis,” is an important and common feature of chronic viral hepatitis, although it may be focal or even absent in cases with minimal or mild necroinflammatory activity. More commonly, the portal tracts appear equally involved by the inflammatory process; hence, variation within the liver may result in sampling error with regard to grading activity. Interface hepatitis has two main morphologic components: a mononuclear inflammatory infiltrate involving hepatocytes located at (and disrupting) the limiting plate, and injury or necrosis of periportal hepatocytes. Lymphocytes and plasma cells in the periportal infiltrate are closely associated with degenerating hepatocytes (Fig. 46.7), such that indentation of the cytoplasm of the hepatocytes occurs, and one might even see engulfment of inflammatory cells by hepatocytes. Hepatocytes in areas of interface hepatitis–associated necrosis often appear pale or swollen and show clumping of cytoplasm. Apoptotic bodies may be present as well.

Lobular Necroinflammatory Activity

In chronic viral hepatitis, hepatocyte necrosis is usually variable in severity and spotty in distribution. Lobular disarray, a feature characteristic of acute hepatitis, is not often prominent in chronic hepatitis unless there is marked activity. Apoptotic hepatocytes (acidophil bodies), which are usually more numerous in the periportal areas, may also be scattered in the hepatic lobules (Fig. 46.8). Mononuclear inflammatory cells tend to cluster around injured or dying hepatocytes (Fig. 46.9). Kupffer cells, in areas of spotty hepatocyte necrosis, may contain phagocytosed cellular debris. Hepatocyte swelling may be present in exacerbations of chronic viral hepatitis and may also be associated with zone 3 cholestasis. Regeneration of hepatocytes is recognized by the formation of liver cell plates that are two cells thick and by the formation of regenerating hepatocyte rosettes.

Fibrosis

Progressive fibrosis of the limiting plate, as a result of continued necroinflammatory activity, leads to enlargement of the portal tracts and stellate periportal fibrous extensions (Fig 46.10). Deposition of collagen and other extracellular matrix materials in the space of Disse at the leading edge of periportal fibrosis also results in capillarization of the sinusoids. Portal-portal fibrous septa represent the fibrous linkage of adjacent fibrotic portal tracts (Fig. 46.11). Portal-central fibrous bridges may also develop from superimposed episodes of severe lobular necroinflammatory activity involving zone 3 of the hepatic lobules. Central-central bridges form by the same mechanism but are far less common in chronic viral hepatitis. The end result of bridging fibrosis is cirrhosis, which is usually macronodular or of a mixed micronodular and macronodular type.

Nomenclature and Scoring

In the past, the term chronic active hepatitis was used to describe liver biopsies with interface hepatitis, and the term chronic persistent hepatitis was used for biopsies with portal inflammation but without significant periportal/piecemeal necrosis. This distinction was thought to be clinically important, because chronic persistent hepatitis was considered a relatively benign process without progression to significant liver disease. However, on identification of hepatitis C and on recognition of the waxing and waning nature of the disease and the prolonged time to progression to cirrhosis in many cases, this nomenclature has been abandoned. Currently, the recommended practice is to use the term “chronic hepatitis”³¹ and include a statement in the pathology report regarding severity of necroinflammatory activity (grade), extent of fibrosis (stage), and etiology.³² Prognostic factors should also be noted in the report (see later discussion).

Several different systems for scoring necroinflammatory activity and fibrosis have been developed. The original Knodell system, published in 1981, served as the prototype semiquantitative liver inflammation and fibrosis scoring system.³³ With modifications—such as the one proposed by Ishak and co-workers, which separates the grade of inflammation and necrosis from fibrosis—this system is still widely used, particularly in therapeutic trials in which the necroinflammatory activity in pretreatment and posttreatment liver biopsy specimens are compared.^34,35 In the original Knodell system, periportal necrosis (with or without bridging necrosis, intralobular necrosis, and inflammation), portal inflammation, and fibrosis are all assigned numeric values, which are then added to obtain a hepatitis activity index (HAI) that ranges from 0 to 22. One major criticism of this system is the inclusion of fibrosis (stage) as a determinant of activity (grade). In practice, the HAI is often modified so that bridging necrosis is dissociated from interface hepatitis, and only the elements that relate to grade are added together to produce the modified HAI (mHAI), with scores that range from 0 to 18; the stage, which indicates degree of fibrosis, is reported separately³⁶ (Table 46.6). An alternative grading system used by the French METAVIR Cooperative Study Group evaluates only two features (periportal necrosis and lobular necroinflammatory activity) instead of three; portal inflammation is excluded because it is considered a prerequisite for the diagnosis of chronic hepatitis, even in cases without parenchymal activity.³⁷

The various semiquantitative grading schemes, although useful for evaluating the effects of a particular treatment regimen in clinical trials, are typically not necessary or clinically relevant for routine pathology reporting of liver biopsies. For everyday diagnostic purposes, simpler schemes are sufficient. For instance, the Batts-Ludwig scoring system (Table 46.7) uses five categories (0 through 4) separately for both grade and stage³⁸ (Fig. 46.12; see also Fig. 46.13). In the Batts-Ludwig system, grade is determined by evaluation of the degree of interface activity (lymphocytic piecemeal necrosis), lobular inflammation, and necrosis. Stage is scored from 0 to 4. A zero score refers to normal connective tissue (no fibrosis). Stage 1 indicates fibrous of portal tracts with expansion; stage 2, periportal fibrosis; stage 3, portal-portal bridging fibrous septa; and stage 4, cirrhosis (Fig. 46.13). Pathologic stage is best evaluated with the use of a Masson trichrome stain, because delicate periportal or early bridging fibrous septa may not be easily apparent on hematoxylin and eosin (H&E) stain.

Prognostic Factors

Factors associated with progression of chronic viral hepatitis to cirrhosis may be divided into those related to specific viruses, host-related factors (see Treatment of Chronic Hepatitis C), and extraneous factors (e.g., alcohol use). For hepatitis C, development of chronic hepatitis is not related to the amount of virus at initial exposure. Viral genotype may be important in the progression of HCV infection. For instance, genotype 1 is associated with more severe disease than genotype 2.^10,55 However, other studies have not confirmed this association.⁵⁶ Host-related factors for disease severity are incompletely defined, but age at infection and gender appear to be relevant. Males and older individuals are more likely to show progression of fibrosis.^56,57 Alcohol consumption increases replication of hepatitis C and is associated with more severe disease.¹¹ In general, the grade of hepatic necroinflammatory activity in liver biopsy specimens correlates with the serum HCV RNA level,⁵⁸ and the rate of progression to cirrhosis correlates with high-grade activity and advanced stage in initial liver biopsies.⁵⁹ Hepatic steatosis is also associated with increased disease severity and is more commonly seen in infections with genotype 3b, as previously discussed.^57,60 Accumulation of iron in hepatocytes and Kupffer cells in hepatitis C may influence the disease course and response to therapy adversely.^57,61 However, many patients with chronic viral hepatitis, including hepatitis C, have abnormal results on serum iron studies but normal or only scant iron accumulation within the liver tissue.

Differential Diagnosis

The morphologic patterns of chronic viral hepatitis may resemble a variety of hepatitides and therefore are not specific (see Table 46.5). The initial distinction should include separation of acute from chronic hepatitis and then chronic viral hepatitis from other forms of chronic hepatitis, such as autoimmune hepatitis, primary sclerosing cholangitis (PSC), primary biliary cirrhosis (PBC), metabolic disorders, and drug reactions. Distinction from acute hepatitis rests primarily on the pattern of lobular inflammation and necrosis, and the finding of a predominance of portal inflammatory changes in cases of chronic hepatitis; fibrosis, in particular, is a cardinal sign of disease chronicity. However, in some cases, identification of acute versus chronic hepatitis may not be possible on morphologic grounds alone; clinical evidence of chronic disease can be helpful.

Early in the course of disease, portal lymphocytic infiltrates in patients with PBC may resemble chronic viral hepatitis, particularly hepatitis C. Florid-duct lesions and loss of interlobular bile ducts are helpful distinguishing features, because these lesions occur in PBC but not in chronic viral hepatitis. Bile ducts may be infiltrated mildly by lymphocytes in chronic hepatitis C, but the degree of inflammation and duct destruction is not nearly as severe as in PBC. Furthermore, portal granulomas, especially those associated with injured bile ducts, are not a feature of viral hepatitis. Chronic cholestasis is not a feature of precirrhotic chronic viral hepatitis and, by definition, indicates a chronic cholestatic condition. Furthermore, demonstration of increased copper or copper-binding protein by copper stains is helpful to suggest the presence of a chronic biliary disorder. Of course, knowledge of the status of viral serologic studies and other titers, such as the antimitochondrial antibody level, are most helpful in this differential diagnosis.

The morphologic features of PSC, in its early stages, may also overlap with chronic viral hepatitis. Both may show a marked portal lymphocytic infiltrate with interface hepatitis; however, this distinction may be particularly difficult in cases of childhood PSC. Once again, bile duct loss suggests a chronic biliary process; alkaline phosphatase levels are typically higher in PSC, but cholangiography is usually necessary to establish a final diagnosis of PSC. The classic “onion-skinning” periductal concentric sclerosing lesions of PSC are not seen in viral hepatitis. In patients with ulcerative colitis and a liver biopsy that shows a pattern of inflammation suggestive of chronic hepatitis, the possibility of PSC should always be strongly considered.