Steatosis, defined as the accumulation of triacylglycerides in hepatocytes, is a frequent finding in most liver biopsies.¹ As much as 5% of the liver parenchyma may be composed of lipid. By convention, any quantity of lipid that occupies more than 5% of the liver mass is considered pathologic.

Macrovesicular steatosis is an accumulation of lipid droplets of various sizes in hepatocytes in which the cell nuclei are displaced peripherally. It is common to observe small and large droplets in the same cell and to find isolated droplets of lipid.

Microvesicular steatosis has a different appearance and clinical significance. The nuclei of affected hepatocytes are typically centrally located within abundant, foamy-appearing cytoplasm. Special stains, such as Oil Red O, may be necessary to confirm lipid accumulation, whereas in macrovesicular steatosis, the large and small lipid droplets are easily detectable by routine hematoxylin and eosin stain. Diseases associated with microvesicular steatosis are characterized by liver failure and hepatic encephalopathy rather than chronicity and potential fibrosis; the former features are the result of mitochondrial β-oxidation defects. The most common examples of purely microvesicular steatosis are acute fatty liver of pregnancy and Reye syndrome. This process has also been reported in the setting of drug toxicity. Drug-related entities are discussed in Chapter 48.

Alcohol-induced liver disease (ALD) refers to the spectrum of liver disorders directly related to excessive alcohol use. This chapter focuses primarily on the pathologic lesions of the ALD subset characterized by accumulation of fat in the liver parenchyma.

Nonalcoholic fatty liver disease (NAFLD) occurs without significant alcohol use. The clinicopathologic entity is characterized by a variety of hepatic parenchymal injury patterns with more than 5% macrovesicular steatosis.

The term nonalcoholic steatohepatitis (NASH) is in the same clinical setting as NAFLD, but NASH is associated with specific pathologic lesions in the liver. The lesions include various amounts of macrovesicular steatosis, hepatocellular injury (most commonly seen as ballooning), and inflammation in the hepatic lobules or portal tracts, or both. These lesions and others that may be seen in steatohepatitis are discussed in this chapter.

Nomenclature

The term ALD refers to a spectrum of liver diseases and includes large or mixed large and small droplet macrovesicular steatosis with or without lobular and portal inflammation; steatohepatitis with or without fibrosis; alcoholic hepatitis; alcoholic cirrhosis with or without steatosis, steatohepatitis, or alcoholic hepatitis; and alcoholic foamy degeneration. Hepatocellular carcinoma is a recognized consequence of ALD and cirrhosis.

NAFLD has a more limited pathologic spectrum than ALD. NAFLD may manifest as large droplet or mixed large and small droplet macrovesicular steatosis with or without lobular or portal inflammation; steatohepatitis with or without fibrosis; and cirrhosis with or without steatosis or steatohepatitis. All of the features of NAFLD may be seen in ALD, prompting use of the term nonalcoholic fatty liver disease.²^,³ Hepatocellular carcinoma may arise as a consequence of NAFLD-induced cirrhosis and is therefore included in the spectrum of NAFLD lesions. Hepatocellular carcinoma is increasingly recognized in noncirrhotic NAFLD.⁴ However, the true incidence of this neoplastic complication in cirrhotic or noncirrhotic liver is less certain than with ALD.

Although NASH and NAFLD are commonly used terms, neither truly represents the underlying pathophysiologic disease process,⁵^–⁷ and although there are histologic similarities with ALD, there are also dissimilarities between these disorders. The relationship between NAFLD and alcohol use may not be as straightforward as originally thought, because a few studies indicate that some patients may be at risk for liver disease from both causes simultaneously. Modest alcohol use also may protect against the effects of insulin resistance.⁸^,⁹

For diagnostic pathologists, microscopically based diagnoses related to fatty liver disease are best rendered descriptively with terms such as steatosis or steatohepatitis, because in most circumstances, only careful clinical evaluation can determine the true underlying cause of the patient’s illness. Many different types of clinical situations may result in similar histologic findings, and in most cases, knowledge of the patient’s clinical information is essential to establish an accurate cause. This is similar to the situation for most cases of chronic hepatitis. The difference with fatty liver disease is that there are no serologic tests available to diagnose or exclude NAFLD with complete certainty.¹⁰

Alcohol-Induced Liver Disease

Clinical Features

The clinical features of ALD vary considerably. Table 49.1 highlights the primary clinical manifestations of the four main clinicopathologic subtypes of ALD: fatty liver, alcoholic hepatitis, alcoholic cirrhosis, and alcoholic foamy degeneration.

Table 49.1

Symptoms, Signs, and Laboratory Abnormalities of Alcohol-Induced Liver Disease

Symptoms and Signs	Fatty Liver	Steatohepatitis and Alcoholic Hepatitis	Cirrhosis	Foamy Degeneration
Asymptomatic	+++	+	Portal hypertension	−
Right upper quadrant discomfort	+++	Pain, not mild	+ to ++	+
Hepatomegaly	++	++	+ to ++	+
Elevated AST, normal ALT	++	+	+ (normal if abstinent)	++
AST/ALT ratio	AST > ALT	AST/ALT > 1-3 common	AST/ALT > 1	AST > ALT
Marked AST elevation	<5 times normal	As much as 5 times normal	−	++
Marked alkaline phosphatase elevation	−	+/−	−	++
Bilirubin elevation	−	>10 mg/dL	− (unless advanced)	++
Jaundice	−	Cardinal sign	As above	++
Elevated white blood cell count	−	>10,000/mm³	− (may be decreased)	−
Fever	−	+++	+ (with infection)	−
Ascites	−	+++	+ (advanced)	−

ALT, Alanine aminotransferase; AST, aspartate aminotransferase; −, does not occur; +, occurs uncommonly; ++, common; +++, very common.

Patients with ALD and fatty liver may be asymptomatic or may have right upper quadrant discomfort at presentation (see Table 49.1). Patients with alcoholic hepatitis usually have abdominal pain and pancreatitis, whereas patients with cirrhosis and alcoholic foamy degeneration often experience only vague abdominal discomfort. In all forms of ALD, the liver is typically enlarged. Fever, an elevated white blood cell count, and jaundice occur in various degrees with the different forms of ALD and may be related to ALD (e.g., alcoholic hepatitis) or to a secondary infection (e.g., peritonitis caused by alcoholic cirrhosis).

At clinical presentation, patients may have elevated serum levels of aminotransferases (i.e., aspartate aminotransferase [AST] and alanine aminotransferase [ALT]), and a ratio of AST to ALT greater than 1 is useful in the evaluation of patients with ALD. AST levels are typically greater than ALT levels in all forms of ALD. Radiographic evaluation plays a role in screening for hepatocellular carcinoma in patients with cirrhosis and in the clinical care of critically ill patients with pancreatitis and suspected intestinal ileus.

Epidemiology and Prevalence

Worldwide, ALD has no social or ethnic barriers, but it is uncommon in very young and very elderly individuals. Both genders may be affected, although women are at higher risk. In the United States, 7.4% of the population meet the criteria for alcohol dependence or abuse. It is the leading cause of end-stage liver disease and liver-related mortality and follows only heart disease and cancer as the major health issue in the United States.¹¹ The reported rates of per capita liters of alcohol consumed per year by individuals older than 15 years of age varies throughout the world: 13.9 in the Russian Federation; 12.9 in Germany, France, and the United Kingdom; 9.3 to 8.5 in North America, Japan, and Australia; 5.0 in China, Philippines, and Vietnam; 1.3 in Iran and Saudi Arabia; and 0.6 in Afghanistan and Pakistan.¹¹ Alcohol use may combine synergistically with other forms of chronic liver disease to generate progressive disease, malignancy, and morbidity.¹²

Familial Associations

Family, twin, and ethnic studies have confirmed a genetic susceptibility to ALD.¹¹ Factors under investigation include gender, genes involved in the metabolism of alcohol (particularly in East Asians), cytochrome P450 2E1 (CYP2E1) and other enzymes involved in the pathways of oxidative stress, various cytokines (e.g., tumor necrosis factor-α [TNF-α], interleukin 10 [IL10]), genes involved in the oxidation of hepatic fat, mechanisms of matrix deposition and degradation in fibrosis, and immune reactions to endotoxin and toxic adducts.¹³

Risk Factors

Liver disease does not develop in all individuals who abuse alcohol. The risk for ALD, even among heavy drinkers, is less than 10% to 15%. Known risk factors include the amount of alcohol consumed during a 10- to 20-year period (>60 g/day for men; 20 to 30 g/day for women), gender (female > male), central obesity, patterns of consumption (nonmealtime > mealtime; daily > weekend only; various types of beverages rather than one type), associated medications (acetaminophen), amount of coffee intake, and genes that regulate expression of proinflammatory cytokines and immune response mechanisms.¹³^–¹⁸ A sequence variation in the patatin-like phospholipase 3 (PNPLA3) gene, which encodes adiponutrin, is associated with the development of cirrhosis in white alcoholics.¹⁹ The same gene variation was previously found to correlate with steatosis in different populations around the world and with features of progressive disease in NAFLD patients.²⁰

Pathogenesis

Alcohol-induced liver damage is a multifactorial process that involves alterations of the gut, gut microbiota, and hepatocellular metabolic pathways and activation of the innate and adaptive immune systems. Resultant outcomes are activation of proinflammatory and profibrogenic molecular mechanisms in specific liver cells.

The primary mechanism of alcohol-induced liver injury is hepatocellular oxidative stress.²¹^,²² Ethanol is metabolized to acetate in the liver mainly by two enzyme systems: the dehydrogenases (i.e., alcohol and aldehyde), which produce acetate and result in steatosis, and the microsomal ethanol-oxidizing system (MEOS). The direct hepatotoxic effects of alcohol are caused primarily by acetaldehyde. Oxidative stress and free radical production result in mitochondrial damage, depletion of the antioxidants such as reduced glutathione, toxicity by free radicals, and induction of lipid peroxidation. Acetaldehyde-formed toxic adducts bind to proteins and lead to additional hepatocellular injury, serve as neoantigens for initiation of the adaptive immune response, and promote collagen production by hepatic stellate cells. The net effect of acetaldehyde production in hepatocytes is the accumulation of intracellular proteins, lipids, water, and electrolytes with the loss of the hepatocyte structural keratins 8 (K8) and 18 (K18). Histologically, they manifest as cellular enlargement, ballooning, empty-appearing cells, steatosis, and loss of immunoreactivity for K8 and K18.²³^,²⁴

The key enzyme of the MEOS is the ethanol-inducible CYP2E1, which is located primarily in the endoplasmic reticulum of acinar zone 3 hepatocytes. Activation of this enzyme system results in the production of reactive oxygen species, such as hydrogen peroxide (H₂O₂) and superoxide anions (O₂⁻), which cause further lipid peroxidation of cell membranes. This enzyme system also metabolizes acetaminophen and produces the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). Even small amounts of acetaminophen may augment depletion of the antioxidant capabilities of the liver in chronic alcoholism.

Other sources of ethanol-induced oxidative stress include endotoxin-activated Kupffer cells, functionally impaired mitochondria, and ferric iron accumulation. Oxidative stress promotes hepatocellular injury, apoptosis, and necrosis; proinflammatory cytokine production (e.g., TNF-α, IL1, IL6); and parenchymal inflammation with polymorphonuclear leukocytes (PMNs) and mononuclear cells and perisinusoidal fibrosis.²⁵^,²⁶

Excessive alcohol intake leads to increased gut permeability and increased portal venous exposure to gut-derived endotoxins. This process results in Kupffer cell activation through the CD14/toll-like receptor 4 (TLR4) complex and activation of the innate immune response.²²^,²⁶

Increased lactate production, another downstream effect of ethanol metabolism, manifests as hyperuricemia and impaired carbohydrate metabolism. Hypoglycemia may occur. Chronic alcohol use impairs protein production and secretion. Multiple aberrations of lipid metabolism result in increased triglyceride production and subsequent accumulation (i.e., steatosis).

The mechanisms of fibrosis are under active scientific investigation. Ultimately, there is an imbalance between collagen deposition and degradation by activated hepatic stellate cells and portal myofibroblasts. Unique to ALD is the additional involvement of hepatocytes and sinusoidal endothelial cells in fibrogenesis through the production of transforming growth factor-β (TGF-β) and fibronectin isoforms.²⁷ Hypoxia induced by ethanol metabolism in zone 3 hepatocytes upregulates vascular endothelial growth factor.²⁶^,²⁷

Pathology

Grossly, steatosis enlarges the liver and imparts a greasy appearance. Livers with advanced fibrosis or cirrhosis may be enlarged and firm and contain micronodules (≤3 mm in diameter) scattered throughout the parenchyma. In some cases, fibrotic livers may be small and firm. With time, the nodules may coalesce to form larger ones, at which point determination of the underlying cause may not be possible. Hepatocellular carcinomas typically stand out on background cirrhosis as raised, green-tinged or darker nodules that usually are larger than 8 mm in diameter.

The histologic pattern of tissue injury in patients with alcohol-induced fatty liver disease initially involves acinar zone 3 (roughly equivalent to perivenular) hepatocytes. In patients with cirrhosis, steatosis or steatohepatitis may or may not persist.

Steatosis

Steatosis, the earliest pathologic finding in ALD, is not consistently found in all forms of ALD.²¹^,²⁸ Alcoholic steatosis is typically macrovesicular and is characterized by large intracellular droplets of lipid in hepatocytes (single or multiple) that peripherally displace the cell nucleus. A minor component of lobular chronic inflammation or mild portal inflammation may be identified, but fibrosis is usually absent.

Steatohepatitis

Steatohepatitis is defined by the presence of both steatosis and hepatocyte injury. Injured hepatocytes may appear ballooned, apoptotic, or lytic. Confluent and bridging necrosis are rarely found in ALD.

Hepatocellular ballooning is considered an essential feature of steatohepatitis by most hepatopathologists.⁷ Ballooned hepatocytes are enlarged cells with rarefied, reticulated cytoplasm (Fig. 49.1) that may or may not contain fat droplets and intracytoplasmic material referred to as Mallory-Denk bodies (MDBs) or Mallory hyaline. Ballooned hepatocytes are located predominantly in zone 3 and are commonly associated with some degree of perisinusoidal fibrosis (Fig. 49.2).²⁹

FIGURE 49.1 In the photomicrograph, ballooned hepatocytes are easily distinguished from the surrounding normal hepatocytes.

FIGURE 49.2 The ballooned hepatocyte in the center of the field is located among steatotic hepatocytes and is adjacent to fibrous tissue. There is a poorly formed Mallory-Denk body in the ballooned hepatocyte.

Apoptotic hepatocytes, also called acidophil bodies, are common in patients with alcoholic steatohepatitis. These round, eosinophilic fragments of cytoplasm located in the hepatic sinusoids may or may not retain nuclear pyknotic material. Lobular inflammation in patients with steatohepatitis is usually mild and consists of mixed acute and chronic or mainly chronic inflammation. Scattered lobular microgranulomas and lipogranulomas are often observed. Lobular lipogranulomas may consist of multiple or single fat droplets surrounded by mononuclear cells and eosinophils (Fig. 49.3). Large portal lipogranulomas are frequently observed in ALD.³⁰ PMNs may be observed in small clusters adjacent to ballooned hepatocytes or shrunken, eosinophilic (apoptotic) hepatocytes that contain MDBs. When PMNs are found next to hepatocytes that contain MDBs, the lesion is often referred to as satellitosis (Fig. 49.4).

FIGURE 49.3 Mixed large and small droplet steatosis. Each of the two lipogranulomas (center) consists of a single droplet of fat surrounded by pigmented Kupffer cells.

FIGURE 49.4 Two areas of satellitosis are evident in this field. Polymorphonuclear leukocytes surround hepatocytes harboring hyaline material. Other nearby hepatocytes contain fat.

Although common, MDBs and satellitosis are not required for the diagnosis. MDBs are not specific to ALD; the structures are seen in NAFLD, chronic cholestatic liver disease, copper toxicity, and amiodarone toxicity. In steatohepatitis of any origin, MDBs are usually found in zone 3 hepatocytes (Fig. 49.5) and are more common in areas of perisinusoidal fibrosis, whereas in chronic cholestasis, copper toxicity, and amiodarone toxicity, MDBs are more common in periportal hepatocytes.¹^,⁶ MDBs may also occur in focal nodular hyperplasia, hepatocellular adenoma, and hepatocellular carcinoma.³¹ MDBs can often be visualized by trichrome stains (Fig. 49.6) and confirmed by the use of immunohistochemistry for K8, K18, ubiquitin, or dynactin 4 (DCTN4, formerly designated p62).³²

FIGURE 49.5 Numerous Mallory-Denk bodies are seen in a biopsy specimen from a patient with alcoholic steatohepatitis are shown.

FIGURE 49.6 A large, ropy Mallory-Denk body is seen near the lower right portion of the terminal hepatic vein (trichrome stain).

Some cases of ALD may show predominantly portal lymphocytic inflammation in the absence of serologic evidence of chronic hepatitis B virus (HBV) or hepatitis C virus (HCV) infection. This feature may correlate with the degree of fibrosis³³ and may reflect an associated autoimmune component to the underlying liver disease.³⁴ Acute inflammation accompanied by a ductular reaction in portal tracts (i.e., pericholangitis) may represent concurrent pancreatitis, whereas increased numbers of portal macrophages may indicate recurrent partial biliary obstruction.³⁰

Alcoholic Hepatitis

Patients with alcoholic hepatitis might not have steatosis. Histologic features of alcoholic hepatitis include hepatocyte ballooning, apoptotic bodies, MDBs with satellitosis, canalicular cholestasis, dense perisinusoidal fibrosis, and a perivenular lesion often referred to as sclerosing hyaline necrosis (i.e., MDBs, satellitosis, and obliterative fibrosis of the outflow vein). Portal hypertension may occur with sclerosing hyaline necrosis. Bridging fibrosis and a ductular reaction may be identified. The absence of steatosis does not rule out alcohol-induced hepatitis.

Alcoholic Foamy Degeneration

Alcoholic foamy degeneration is an unusual and often serious type of ALD associated with marked elevations of aminotransferases, γ-glutamyltransferase (GGT), alkaline phosphatase, and bilirubin.³⁵ Histologically, it is characterized by diffuse, primarily microvesicular steatosis without inflammation or ballooning or by marked fibrosis with or without canalicular cholestasis (Fig. 49.7). MDBs are uncommon. Perivenular and perisinusoidal fibrosis may be evident. Clinically, the disorder mimics extrahepatic biliary obstruction, but the liver biopsy findings can be used to distinguish the two entities. Alcoholic foamy degeneration is reversible with abstinence from alcohol.

FIGURE 49.7 This biopsy was obtained from a patient with known alcoholism, hepatomegaly, and elevated aspartate aminotransferase and bilirubin values. It contains no inflammation, ballooning, or Mallory-Denk bodies, and there is only a minor degree of fibrosis. Diffuse steatosis is evident, and a significant portion is microvesicular.

Fibrosis and Cirrhosis

The characteristic pattern of early fibrosis in patients with noncirrhotic alcoholic steatohepatitis or alcoholic hepatitis is pericellular or perisinusoidal. This pattern results from deposition of collagen in the space of Disse and is commonly referred to as chicken wire fibrosis (Fig. 49.8).

FIGURE 49.8 The dense zone 3 perisinusoidal fibrosis illustrates the characteristic “chicken wire” network of fibrosis.

Fibrosis usually begins in zone 3 of the hepatic acini (Fig. 49.9). This type of fibrosis may be identified with or without steatohepatitis. However, when pericellular or perisinusoidal fibrosis occurs without steatohepatitis, it probably indicates that the patient had at least one prior episode of steatohepatitis. In ALD, perisinusoidal fibrosis may involve large portions of the lobules and become quite dense (Fig. 49.10). In these cases, the patient may also have clinical evidence of portal hypertension despite the absence of cirrhosis.

FIGURE 49.9 On low power, the zone 3 accentuation of steatohepatitis is best appreciated with a trichrome stain. Ballooning, steatosis, and perisinusoidal fibrosis can be seen.

FIGURE 49.10 This biopsy from a patient with chronic alcoholism and portal hypertension shows dense perisinusoidal fibrosis and loss of hepatic architecture. This appearance is common in samples from patients with advanced alcohol-induced liver disease.

Perivenular fibrosis, a thickened sheath of collagen around the outflow veins in the absence of perisinusoidal fibrosis, has been identified in patients with steatosis that subsequently progressed to cirrhosis. This lesion is therefore considered a prognostic indicator of progression if alcohol exposure is continued.²¹

With disease progression, periportal fibrosis may develop (Fig. 49.11), followed in some cases by bridging fibrosis in a central-central, central-portal, or portal-portal pattern. In ALD, regions of parenchymal extinction (i.e., septa) may be quite broad (Fig. 49.12). After cirrhosis is established, areas of perisinusoidal fibrosis may not be evident. Periportal fibrosis and bridging fibrosis are often accompanied by a ductular (proliferative) reaction. In ALD, isolated portal fibrosis in the absence of portal inflammation is uncommon and may be a manifestation of recurrent pancreatitis or biliary obstruction.³⁰ Itoh observed a pattern of portal fibrosis characteristic of ALD known as holly leaf.³⁶ This pattern of fibrosis, which is commonly associated with hemochromatosis, is characterized by portal expansion and nonbridging, small, fibrous extensions or spikes into the surrounding parenchyma that resemble the outline of the holly leaf.

FIGURE 49.11 With progression of fibrosis in alcohol-induced liver disease, periportal fibrosis may be prominent.

FIGURE 49.12 The small nodule is surrounded by broad regions of scar tissue (i.e., parenchymal extinction) in a patient with alcoholic cirrhosis.

In patients with ALD with bridging fibrosis,³⁷ periseptal ductular reaction may be prominent. The ductular reaction, characterized by proliferation of K7- and/or K19-positive ovoid cells forming ductular structures in an inflammatory, stromal matrix,³⁸ less likely represents a cholestatic process in end-stage liver disease,²⁶^,³⁰ but it is most likely the result of impaired regenerative activity of hepatocytes resulting from the anti-regenerative effects of alcohol.³⁹

ALD-associated cirrhosis may be macronodular, micronodular, or mixed. Micronodular nodules are typically less than 3 mm in diameter. Larger nodules may develop when multiple nodules coalesce to form mixed micronodular and macronodular cirrhosis. Macronodular cirrhosis may be difficult to diagnose in a liver biopsy specimen because of the large size of the nodules; clues to abnormal architecture can be sought by use of a reticulin stain. Clusters of oncocytic hepatocytes suggest macronodular cirrhosis (see Chapter 50). Phlebosclerosis and occlusive disease of the terminal hepatic venules and sublobular veins may occur in patients with ALD-induced cirrhosis.⁴⁰

In ALD-associated cirrhosis, periseptal hepatocellular copper granules and, uncommonly, α₁-antitrypsin globules may be found. The role of heterozygosity for genes related to α₁-antitrypsin in promoting damage in patients with ALD is a subject of ongoing debate.⁴¹ Increased iron levels in ALD is discussed later. Pseudotumoral nodules, which correspond to areas of active alcoholic hepatitis in cirrhotic livers, may be recognized on imaging studies and confused for hepatocellular carcinoma. These lesions may result from hypervascularity.⁴²

Other Pathologic Features of Alcohol-Induced Liver Disease

Megamitochondria.

Megamitochondria (i.e., giant mitochondria) are identified by light microscopy as intracytoplasmic, round or cigar-shaped, eosinophilic structures in hepatocytes, and they are most readily seen in hepatocytes that contain microvesicular steatosis (Fig. 49.13). Megamitochondria may also occur in normal pregnancy, acute fatty liver of pregnancy, and Wilson disease.

FIGURE 49.13 A nonzonal group of hepatocytes with tiny fat vacuoles is evident in the cytoplasm. Many of the hepatocytes also contain eosinophilic, round megamitochondria.

Iron Deposition.

Mildly increased iron deposition is common in most forms of ALD. However, in a minority of cases, it may be moderate or severe.²³ Possible reasons for hemosiderosis in ALD include increased dysregulation of hepcidin production,⁴³ intestinal iron absorption, iron in some types of alcoholic beverages, hemolysis related to spur cell anemia, and upregulation of the transferrin receptor.¹⁸ With a modified Perls stain, iron deposition is usually nonzonal.³⁰^,³⁷ In ALD-related cirrhosis,³⁷ iron deposition may vary in quantity between individual regenerative nodules (Fig. 49.14).

FIGURE 49.14 In a patient with alcoholic cirrhosis, the nodule in the center of the field shows prominent iron staining (modified Perls iron stain).

Acute and Chronic Cholestasis.

Any of the following pathologic processes related to ALD may result in intrahepatic cholestasis, which is characterized by intracanalicular bile plugs: severe fatty liver, alcoholic pancreatitis due to gallstones or alcohol, alcoholic foamy degeneration, alcoholic hepatitis, and decompensated alcoholic cirrhosis. Canalicular bile thrombi are observed in 15% to 32% of livers with ALD (Fig. 49.15). Severe fatty liver with portal tract features of cholangitis and cholestasis is a specific clinicopathologic cholestatic syndrome in patients with ALD. Bile stasis in ALD also may be a manifestation of superimposed viral hepatitis or drug-induced jaundice.²¹ In patients with established ALD-associated cirrhosis, a copper stain may show mild positivity, which represents chronic retention of bile caused by the cirrhotic remodeling.

FIGURE 49.15 A cholestatic rosette with a central bile plug and several surrounding hepatocytes containing intracellular bile are identified in a biopsy specimen from a patient with fatty liver disease resulting from alcohol-induced liver disease.

In advanced cases of ALD, the cytoplasm of some hepatocytes may have a ground-glass appearance because of smooth endoplasmic reticulum proliferation, or it may be deeply eosinophilic, referred to as oxyphil or oncocytic change because of increased numbers of mitochondria. Both changes are considered adaptive. Historically, their presence was considered indicative of ongoing alcohol consumption, but one research group reported that they might also be observed after periods of prolonged abstinence.³⁰

Vascular Lesions.

Sclerosing hyaline necrosis, which is a marker of severe alcoholic hepatitis, and obliterative vein lesions may be responsible for the development of noncirrhotic portal hypertension in patients with ALD. Sclerosing hyaline necrosis consists of a combination of acinar zone 3 lesions, including dense perivenular and perisinusoidal fibrosis (i.e., sclerosis), occlusion of terminal hepatic venules, MDBs, and liver cell necrosis and loss, which results in the formation of large perivenular scars. Lesions of the terminal hepatic venules and sublobular veins include perivenular fibrosis, phlebosclerosis, and, less frequently, lymphocytic phlebitis (Fig. 49.16).⁴⁰

FIGURE 49.16 There is no evidence of steatosis or steatohepatitis in the biopsy specimen from a patient with alcohol-induced liver disease. The outflow vein is almost obliterated. A small artery branch lies close to the vein, and a ductular reaction is evident at the edge of the developing septum.

Treatment Effects.

Alcoholic steatosis may resolve completely within 4 weeks of alcohol abstinence.³⁰ However, lesions associated with alcoholic hepatitis or steatohepatitis may persist for as long as 6 months after alcohol withdrawal, albeit with decreased severity.⁴⁴ With abstinence, there is usually an increase in the degree of portal lymphocytic infiltration.⁴⁴

Prognostic Lesions.

Perivenular fibrosis in steatosis in the absence of cirrhosis portends progression unless abstinence occurs. Acute cholestasis correlates with poor survival of hospitalized patients with ALD.²¹ These patients have a reduced 5-year survival rate (22%) compared with patients with ALD who have no or mild cholestasis (54%).²³ The number of apoptotic bodies correlates positively with severe histologic and clinical disease activity.⁴⁵^,⁴⁶ Alcoholic hepatitis, sclerosing hyaline necrosis, and severe steatosis represent poor-prognostic lesions in patients with ALD, particularly in those with cirrhosis.²¹^,⁴⁷ In noncirrhotic patients, mixed steatosis and the finding of megamitochondria in the initial liver biopsy of alcoholic patients without steatohepatitis correlate with an increased risk of subsequent fibrosis or cirrhosis on follow-up.⁴⁸ In acute-on-chronic liver failure caused by ALD, marked ductular bilirubinostasis and many MDBs are significant predictors of in-hospital mortality.⁴⁹

Lesions in the Allograft Liver.

Any of the previously described lesions may manifest as recurrent or de novo ALD in a liver allograft. Care is taken to evaluate other features of allografts, particularly acute and chronic rejection and recurrence of hepatitis C (see Chapter 46).

Natural History and Treatment

The financial and social burdens associated with ALD are significant.¹¹^,⁵⁰ Alcoholic hepatitis is associated with a significant risk of hospitalization and loss of time from work, morbidity and short-term mortality, and progression to cirrhosis within 5 years for as many as 70% of individuals. Few affected individuals are able to reverse the disease process with complete abstinence.¹¹ A 12-year historical study from a national registry of Danish subjects comparing biopsy-proven ALD with the general population showed that the cirrhosis risk was higher for affected women than men and twice as high for patients with steatohepatitis than those with pure steatosis.⁵¹

Chronic alcohol abuse is responsible for as many as 45% of cases of hepatocellular carcinoma in Western countries,⁵² a rate that is higher than that for chronic hepatitis C.¹⁸ Coexistent HCV infection has an additive effect on the risk of carcinoma,¹¹ and other comorbid factors, such as chronic hepatitis B, hemochromatosis, obesity, and cigarette smoking, contribute to an increased risk of hepatocellular carcinoma and mortality in patients with ALD.⁵³^,⁵⁴ Intrahepatic cholangiocarcinoma also has been linked to ALD.⁵⁵

The mainstay of treatment for ALD is abstinence from alcohol. One of the pharmacologic methods of treatment of alcoholism, cyanamide, may produce isolated, nonzonal eosinophilic globules in hepatocytes. Treatment of hospitalized patients with alcoholic hepatitis includes steroids and the antioxidants pentoxifylline and S-adenosyl-l-methionine (SAMe). For abstinent patients with cirrhosis, liver transplantation is an accepted treatment option. More controversial is a practice of liver transplantation for patients with acute alcoholic hepatitis.⁵⁶^,⁵⁷

Nonalcoholic Fatty Liver Disease

Clinical Features

Individuals with NAFLD may be asymptomatic or may show mild, nonspecific symptoms such as fatigue and right upper quadrant discomfort or pain (Table 49.2). Fever is not a feature of uncomplicated NAFLD; when present, it suggests a different or concomitant disorder.

Table 49.2

Symptoms, Signs, and Laboratory Abnormalities of Nonalcoholic Fatty Liver Disease

Symptoms and Signs	Fatty Liver	Steatohepatitis	Cirrhosis
Asymptomatic	++	+	Portal hypertension
Right upper quadrant discomfort	++	++	+
Hepatomegaly	++	++	+
Elevated AST, normal ALT	−	−	−
AST/ALT ratio	AST/ALT < 1	AST/ALT < 1	AST/ALT ≥ 1
Marked AST elevation	−	−	−
Marked alkaline phosphatase elevation	−	−	−
Bilirubin elevation	−	−	−
Jaundice	−	−	−
Elevated white blood cell count	−	−	−
Fever	−	−	−
Ascites	−	−	+ (advanced)

ALT, Alanine aminotransferase; AST, aspartate aminotransferase; −, does not occur; +, occurs uncommonly; ++, common; +++, very common.

The most common clinical feature of NAFLD is central (truncal or abdominal) obesity, which is best assessed by measurement of waist circumference. For adult men, central obesity is a waist circumference greater than 102 cm, and for adult women, it is greater than 88 cm. Obesity is defined by body mass index (BMI), which is the weight in kilograms divided by the height in meters squared (kg/m²). Compared with waist circumference, it is less specific and does not assess the anatomic location of the metabolically unique subcutaneous and visceral fat depots or shape of the body habitus. For non-Asian adults, the current definitions used are overweight (BMI > 25 kg/m²) and obesity (BMI > 30 kg/m²). Because the Asian body habitus is deceptively thin and able to conceal visceral adiposity, lower BMI values for overweight and obesity have been recommended.⁵⁸

Clinical evidence of hepatomegaly may be found in patients with an enlarged, fatty liver. Ascites and other features of portal hypertension may be identified in patients with NAFLD-associated cirrhosis. Obstructive sleep apnea and acanthosis nigricans are recognized associations of NAFLD.

Laboratory values commonly assessed for patients with NAFLD include ALT, AST, and GGT. Patients also undergo tests for hyperglycemia (glycated hemoglobin [HbA_1c] is used to evaluate long-term glycemic control), tests for insulin resistance (based on calculations of fasting glucose and insulin levels by using quantitative insulin sensitivity check index [QUICKI] and homeostasis model assessment [HOMA-IR]), and tests of lipid parameters.²¹

The overall sensitivity of liver enzymes for detection of fatty liver disease is poor.²¹^,⁵⁹^,⁶⁰ For instance, patients with normal ALT levels may have steatosis or advanced steatohepatitis⁶¹ or silent cirrhosis.⁶²^,⁶³ If elevated, the ALT value is greater than the AST value, and an ALT/AST ratio greater than 1 is often found in cases of precirrhotic NAFLD; the reverse situation occurs in ALD. Autoantibodies, particularly antinuclear antibody and rarely antimitochondrial antibody, have been reported in as many as 34% of individuals with NAFLD.⁶⁴ In some, only further detailed clinical testing or liver biopsy can distinguish autoimmune hepatitis from concurrent autoimmune hepatitis with NAFLD or NAFLD alone.⁶⁴ A possible association of autoantibodies with more severe disease has been suggested but not confirmed.⁶⁵^,⁶⁶ In combination with the proven lack of reproducible gross evaluation of the liver by surgeons, authorities recommend a liver biopsy for all high-risk and bariatric patients,⁶⁷^–⁶⁹ especially when other causes of steatosis have been excluded.⁵⁹

Abnormal iron study results are a common feature in patients with NAFLD. For instance, elevated serum levels of ferritin (but not transferrin saturation) may be found in patients with NAFLD and may cause clinical concern about an iron overload disorder.⁷⁰ The serum ferritin level in NAFLD patients has been reported as an independent predictor of the histologic severity of underlying liver disease.⁷¹ An elevated serum ferritin level may indicate hepatocyte necrosis and systemic inflammation, and it is a recognized feature of the metabolic syndrome (discussed later). However, iron overload itself is not a feature of type 2 diabetes mellitus. The associations of iron dysregulation, HFE (hemochromatosis) mutations, and fibrosis with the metabolic syndrome remain subjects of debate.⁷⁰ A meta-analysis did not support an association between HFE genetic variants and NAFLD.⁷²

The proinflammatory iron regulator hepcidin is expressed in the liver and adipose tissue of obese patients, and this finding correlates with low transferrin values in 68% and anemia in 24% of these individuals.⁷³ Demonstration of hepcidin mRNA and protein in adipose tissue is a new finding and is the subject of iron and adipokine studies.⁷³

Laboratory tests are indicative of the complexity of this condition. Markers of systemic inflammation, such as elevated levels of C-reactive protein, fibrinogen, and plasminogen activator inhibitor 1, are found in the setting of NASH and fibrosis.⁷⁴ A depressed level of adiponectin, an endocrine product of visceral adipose tissue, is recognized as a pathologic feature of NAFLD or NASH.⁷⁴ Some work has implicated additional factors as being proinflammatory (e.g., hemoglobin) in subsets of individuals with NAFLD but without the metabolic syndrome.⁷⁵ In contrast with ALD, leukocytosis, cholestasis, and jaundice are not typical features of uncomplicated, noncirrhotic NASH.

By ultrasonography, computed tomography (CT), or magnetic resonance imaging (MRI), the characteristic finding in NAFLD is increased hepatic fat. The ultrasound finding is referred to as a bright liver. Newer types of imaging studies use methods to semiquantitate the lipid content of the liver.⁷⁶ However, when steatosis involves less than 33% of the liver parenchyma, imaging tests may not detect it.⁷⁷ Imaging is also not an adequate replacement for tissue analysis for determination of the degree of disease activity or the stage of fibrosis in patients with precirrhotic NASH.⁷⁸

Epidemiology and Prevalence

The epidemiology and prevalence of NAFLD are understood in terms of its relationship with obesity and increased risks of stroke and heart disease, a group of associations referred to as metabolic syndrome. The common underlying feature of this syndrome is systemic insulin resistance. Studies have confirmed associations of NAFLD with hepatic insulin resistance, cardiovascular diseases,⁷⁹ and the metabolic syndrome in adults⁸⁰ and children.⁸¹ In one definition of metabolic syndrome, a patient must have at least two of the following disorders plus type 2 diabetes mellitus, insulin resistance, or glucose intolerance: obesity (BMI ≥ 30); arterial hypertension (≥140/90 mm Hg); dyslipidemia as low levels of high-density lipoprotein (<0.9 mmol/L) or hypertriglyceridemia (>1.7 mmol/L); and microalbuminuria (>20 µg/min).⁸² The sole finding of fatty liver may indicate progression of the metabolic syndrome⁸³ and progression of liver disease.⁸⁴

NAFLD is a worldwide disorder and has been documented in almost all cultures. This global phenomenon is closely related to acquisition of a Western diet and lifestyle, which includes less physical activity. Initially thought to be a disease predominantly of overweight women, the entire spectrum of NAFLD is now recognized as common among men of all ages, but severe NASH and advanced fibrosis remain more common among adult women.²¹^,⁵⁹ Several studies have confirmed an underrepresentation of this disease process in African Americans of all age groups and an overrepresentation in Hispanics.⁵⁹

Once referred to as a disease of the affluent, NAFLD has become recognized as everyman’s disease.⁸⁵ Future projections of the rates of obesity, type 2 diabetes mellitus, and their complications in the developing world for the year 2030 are staggering. They range from 18.6% in sub-Saharan Africa to 79.4% in India. The projected percent positive change for type 2 diabetes mellitus incidence is 32% in Europe, 72% in the United States, 150% in India, 162% in sub-Saharan Africa, and 164% in the Middle East.⁸⁶

Having considered the worldwide and multicultural nature of NAFLD, some studies have evaluated certain ethnic proclivities for development of this disease. For instance, an image-based study of hepatic steatosis from a large, urban, multiethnic population in the United States⁷⁶ found the following relative prevalence rates: Hispanic > white > African American. Results from a subsequent clinic-based study that used liver tests and liver biopsy results differed only slightly,⁸⁷ showing the following ethnic prevalence rates: white > Hispanic> Asian. African Americans represented only 3% of patients in this cohort. Others have observed an apparent underrepresentation of African Americans in cohorts of patients with NAFLD.⁸⁸ A small biopsy series from an inner-city hospital in the United States that primarily serves African Americans confirmed the relative scarcity of the disease in this patient population. Less than 2% of 320 liver biopsies showed clinicopathologic evidence of NAFLD, even though the BMI of the cohort was between 26.9 and 32.7.⁸⁹

Unfortunately, most of the early prevalence studies were performed without a full understanding of the link between the metabolic syndrome and fatty liver disease. In later studies, surrogate markers such as elevated ALT levels and a bright liver on ultrasound were used to examine study populations. However, similar to pathologic studies, the results vary widely, which is partly related to the criteria used to define the positivity of test values. For instance, in studies that relied on elevated serum aminotransferase levels, recognized shortcomings included underrecognition of positive cases with normal test values, determination of criteria for normal values in an increasingly obese population,⁸⁴ determination of reliable ALT values from frozen sera, and ascertainment of the levels of alcohol intake.⁹⁰ Methods of assessment of body habitus (i.e., BMI, waist-to-hip ratio, midthigh measurements, and more sophisticated and expensive calculations) also vary.⁷⁸ Commonly cited studies are listed in Table 49.3.

Table 49.3

Prevalence of Nonalcoholic Fatty Liver Disease among U.S. Adults Based on NHANES III Data*

Study	Criteria	Prevalence of NAFLD
Clark et al, 2002²⁷⁴	Any elevation of AST, ALT, GGT	23% of all U.S. adults
		31% male
		16% female
		39% of obese men, 40% of obese women
Clark et al, 2003²⁷⁵	± patients with diabetes	AST > 37 U/L, ALT > 40 U/L (men)
		AST, ALT > 31 U/L (women)
		7.9% of all U.S. adults; 69% unexplained (5.5% of adults)
Ruhl and Everhart, 2003²⁷⁶	Elevated ALT only; excluded patients with diabetes	ALT > 43 U/L (men and women)
Ruhl and Everhart, 2003²⁷⁶	Elevated ALT only; excluded patients with diabetes	2.8% elevated ALT, 65% explained by elevated body mass index

^* Limitations of NHANES data: autoimmune hepatitis, primary biliary cirrhosis, Wilson’s disease, and α₁-antitrypsin deficiency not excluded rigorously and absence of liver pathology for confirmation or exclusion.

ALT, Alanine aminotransferase; AST, aspartate aminotransferase; GGT, γ-glutamyltransferase; NAFLD, nonalcoholic fatty liver disease; NHANES III, Third National Health and Nutrition Examination Survey.

Validation of the findings of the Third National Health and Nutrition Examination Survey (NHANES III) has emerged from subsequent studies. One calculated hepatic lipid levels by proton magnetic spectroscopy in a multiethnic population in the southwestern United States and found that 31% of 2287 unselected individuals had a greater than 5.5% rate of hepatic steatosis. Of these, 79% had normal ALT values.⁷⁶ A contemporaneous study from a large clinic population in California showed that of 742 individuals with newly diagnosed chronic liver disease, 21.4% had NAFLD.⁸⁷ NAFLD was found to be the most common cause of incidental liver function test abnormalities (26.4%) in a U.K. prospective primary care cohort of 1118 adults by a combination of ultrasound and biomarker assays; ALD was a close second (25.3%). Of the NAFLD cases, 7.6% had evidence of previously undetected advanced fibrosis.⁹¹

A U.S. biopsy-based prevalence study of asymptomatic adults found that 46% of 156 adult, unselected patients who had steatosis on ultrasound had NAFLD diagnosed on biopsy. Of the biopsied NAFLD patients, 30% had diagnostic NASH, and 2.7% of those with NASH had advanced fibrosis (≥stage 2). This finding allowed speculation that more than 2 million of the U.S. adult population was at risk for advanced fibrosis because of NASH. These findings led the researchers to conclude that the prevalence of NAFLD was greater than that of hepatitis C and posed a serious concern for the future of health care.⁹²

A study in a predominantly nonaffluent, nonobese population in India represented by 1911 inhabitants of a rural community showed the prevalence of NAFLD diagnosed by ultrasonography and CT to be 8.7%. NASH was seen in 31% of 36 biopsied persons with potentially significant disease, 4 of whom had cirrhosis.⁹³^,⁹⁴

The estimated prevalence rate of NAFLD in the United States is greater than that of ALD (Table 49.4). It may affect as many as 5% of the adult population, with an even higher rate among patients with type 2 diabetes.⁵⁹ Table 49.5 summarizes several published series focused on histologic documentation of fatty liver in adult autopsies. Correlations between body weight and diabetes were discussed in many of these studies long before the metabolic syndrome was identified as a specific entity. More than one investigator suggested that steatosis was a normal consequence of aging (see Pathogenesis).

Table 49.4

Prevalence Estimates of Fatty Liver Disease Compared with Other Chronic Liver Diseases

Disorder	Prevalence
Nonalcoholic fatty liver disease	25-75% of obese, diabetic adults 16% of 15- to 19-yr-old adolescents 38% of obese adolescents
Hepatitis C	1.3-2.0%
Alcohol-induced liver disease	1%
Hepatitis B	0.3-0.4%
Hereditary hemochromatosis	1/200-400 of northern European descent
Autoimmune hepatitis, primary biliary cirrhosis, primary sclerosing cholangitis	9-17/100,000
α₁-Antitrypsin deficiency	1/1500-7600
Wilson disease	1/30,000

Data from McCullough AJ. Pathophysiology of nonalcoholic steatohepatitis. J Clin Gastroenterol. 2006;40(suppl 1):S17-S29 and Yu AS, Keeffe EB. Elevated AST or ALT to non-alcoholic fatty liver disease: accurate predictor of disease prevalence? Am J Gastroenterol. 2003;98:955-956.

Table 49.5

Prevalence of Fatty Liver Disease in Autopsy Studies

Study	Population Studied (N)	Prevalence of Fatty Liver	Associated Features
Hilden et al, 1977²⁷⁷	Motor vehicle accident victims; adults (503)	24% overall 0.5% had features of alcoholic hepatitis	Age: 1% < 20 yr 18% 20-40 yr 39% > 60 yr Overweight: associated with steatosis, not age
Underwood Ground, 1982²⁷⁸	Aircrew, accidental deaths, all men (199)	15.6% overall 2.1% had features of alcoholic hepatitis	All healthy; none had overt alcoholism
Hornboll and Olsen, 1982²⁷⁹	678 Consecutive autopsies, all > 20 yr of age (396 with alcohol and other exclusions)	54% overall 43% had < 33% 11% had > 33%	Age: no association after 40 yr Overweight: strong association with degree of fatty change; diabetic people were more common in this group Diabetes not independently associated
Underwood Ground, 1984²⁸⁰	Aircraft, motor vehicle accidents, all men; all accidents associated with alcohol, other illnesses excluded (166)	21%	Questioned possible irregular use of alcohol as factor; discussed increased carbohydrate intake relationship to fatty liver disease
Wanless, 1990¹⁷⁶	Hospitalized, 207 obese patients, 144 matched, nonobese controls; alcoholic patients excluded (351)	Steatosis: 36.3% overall, 29.2 obese, 7.1% lean Steatohepatitis: 18.5% obese, 2.7% lean	Overweight: prevalence and grade of steatosis and steatohepatitis correlated with grade of obesity Diabetes: increased the risk of steatohepatitis and fibrosis
Schwimmer et al, 2006²³¹	Consecutive pediatric and adolescent autopsies in a single county, nonselected (742)	Steatosis: 13% overall 2-4 yr: 0.7% 15-19 yr: 17.3%	Age: fatty liver incidence increased with age Obesity: 38% had fatty liver Ethnicity: Hispanic (11.8%), Asian (10.2%), white (8.6%), African American (1.5%)

In summary, the true prevalence rate of NAFLD remains unknown because there are no reliable or specific noninvasive tests available for an accurate diagnosis or exclusion of this process. A review of noninvasive markers in NAFLD, NASH, and fibrosis indicates the efforts in the field.²¹ Although liver biopsy evaluation is considered the gold standard of diagnostic tests, it cannot be considered an appropriate screening tool. Results from biopsy studies reinforce the observations that not all obese individuals have hepatic steatosis⁸^,⁹⁵^,⁹⁶ and that unexplained elevated ALT values cannot be assumed to indicate fatty liver disease. For example, Skelly and colleagues⁹⁷ showed that as many as one third of 354 biopsies performed for unexplained elevated ALT levels were histologically normal or had abnormalities because of liver diseases other than NAFLD or NASH. Recommendations for the focused role of liver biopsy for patients with suspected NAFLD or NASH were discussed in the practice guidelines from the American Association for the Study of Liver Diseases⁵⁹ and in a consensus conference of the European Association for the Study of the Liver.⁶⁹

Familial Associations and Risk Factors

The genetic predispositions found in NAFLD are exemplified by differences in the incidence of other risk factors, such as obesity, diabetes, hypertension, and hyperlipidemia, among various ethnic populations. Studies have documented fatty liver disease and cirrhosis among kindreds.⁹⁸ One study of 20 patients showed a trend toward familial clustering and maternal linkage for insulin resistance among patients with NAFLD.⁹⁹

Type 2 diabetes and obesity are risk factors for progressive disease in clinical¹⁰⁰ and histologic studies.⁸^,¹⁰¹^,¹⁰² Various possible environmental and genetic factors have been proposed for NAFLD,¹³^,¹⁰³ including the type of diet, exercise, smoking,¹⁰⁴ the role of small bowel bacterial overgrowth, endotoxin and related immune or cytokine responses, polymorphisms for genes that control fatty acid oxidation (e.g., microsomal transfer protein), and fibrosis (i.e., angiotensinogen and TGF-β).

Broad, nonexclusive categories of genes under investigation as potential risk factors for NAFLD¹⁰⁵ include those involved in the control of adiposity and insulin resistance (e.g., peroxisome proliferator–activated receptor-γ [PPAR-γ], central versus peripheral fat depots); determinants of hepatic steatosis (i.e., free fatty acid delivery and de novo lipogenesis, processing, and egress); hepatic fatty acid oxidation pathways (e.g., mitochondrial, peroxisomal, microsomal); hepatic oxidative stress mechanisms (e.g., production, defense); cytokine effects (e.g., TNF-α, IL6, adipokines); and determinants of progression of fibrosis. One genomic and proteomic study of 98 bariatric patients found downregulation of genes involved in defense against oxidative stress in NAFLD cases and upregulation of genes associated with fibrogenesis and apoptosis in steatohepatitis cases.¹⁰⁶

Genome-wide association and candidate gene studies have identified a variant in PNPLA3, which encodes adiponutrin, an insulin-responsive phospholipase involved in lipolysis and lipogenesis that correlates with accumulation of hepatic triglyceride and some histologic features of severity of NASH with identical ethnic distributions in prevalence studies.¹⁰⁷^–¹¹² This association is not limited to adults.¹¹²^,¹¹³ The effects cannot be shown to be direct, and it is speculated the allelic variant results in sensitization of the liver to metabolic and environmental stressors.²⁰

Pathogenesis

Certain similarities (i.e., steatosis, oxidative damage, and cytokine response) and dissimilarities between the pathogenesis of NAFLD and ALD are highlighted in Figure 49.17. The most commonly discussed driver of NAFLD is insulin resistance and the associated lipotoxicity (i.e., fat in nonfat depots) and complex pathways of systemic and local inflammation.¹¹⁴ The metabolic system of insulin involves signaling among skeletal muscle, adipose tissue, and liver.¹¹⁵^–¹¹⁸

FIGURE 49.17 Alcohol-induced liver disease and nonalcoholic (obesity and insulin resistance related) fatty liver disease share several pathogenetic processes, which are shown in the overlapping portions of the Venn diagram. Conditions unique to each disease are highlighted in the nonoverlapping sections. CTGF, Connective tissue growth factor; CYP2E1, cytochrome P450 2E1; F, female; FFA, free fatty acids; IL-6, interleukin-6; LPS, lipopolysaccharides; M, male; MEOS, microsomal ethanol-oxidizing system; ROS, reactive oxygen species; TLRs, Toll-like receptors; TNF-α, tumor necrosis factor-α; ↑, increased levels.

The manifestations of insulin resistance depend on the type of tissue involved. In visceral adipose tissue, there is unabated release of free fatty acids into portal venous blood. In peripheral muscle, insulin resistance manifests as an inability to use circulating glucose. In liver, continuation of glucose production (i.e., gluconeogenesis) combines with a lack of glycogen storage in the setting of hyperinsulinemia and hyperglycemia. Hepatic steatosis, which corresponds to an accumulation of triglycerides in hepatocytes, results from an imbalance between the delivery of free fatty acids and endogenous lipogenesis and fatty acid disposal through oxidation and packaging of esterified fatty acids and triglycerides for export by apolipoproteins as very-low-density lipoproteins. Each of these steps involves complex, genetically regulated pathways.

Current work shows that triglyceride accumulation is a mechanism of sequestration of potentially damaging free fatty acids and that nontriglyceride fatty acid metabolites likely drive subsequent necroinflammatory lesions recognized as NASH.¹¹⁹ Our understanding of pathogenesis of NAFLD and NASH also includes the roles of altered gut microbiota,¹²⁰ intestinal permeability and lipopolysaccharide (LPS) exposure,¹²¹ differential macrophage activation in adipose tissue depots,¹²² innate immunity,¹²³^,¹²⁴ and supporting activation by inflammasomes in obesity-related liver injury.¹²⁵

Visceral (abdominal) adipose tissue is an energy storage depot and a source of highly active proteins, collectively referred to as adipokines or adipocytokines (Fig. 49.18

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