Parts of this article (those related to the use of the new 2023 nomenclature) need to be updated.(November 2023) |
Fatty liver | |
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Other names | Hepatic steatosis |
Micrograph showing a fatty liver (macrovesicular steatosis), as seen in non-alcoholic fatty liver disease. Trichrome stain. | |
Specialty | Gastroenterology |
Symptoms | None, tiredness, pain in the upper right side of the abdomen [1] [2] |
Complications | Cirrhosis, liver cancer, esophageal varices [1] [3] |
Types | Non-alcoholic fatty liver disease (NAFLD), alcoholic liver disease [1] |
Causes | Alcohol, diabetes, obesity [3] [1] |
Diagnostic method | Based on the medical history supported by blood tests, medical imaging, liver biopsy [1] |
Differential diagnosis | Viral hepatitis, Wilson disease, primary sclerosing cholangitis [3] |
Treatment | Avoiding alcohol, weight loss [3] [1] |
Prognosis | Good if treated early [3] |
Frequency | NAFLD: 30% (Western countries) [2] ALD: >90% of heavy drinkers [4] |
Fatty liver disease (FLD), also known as hepatic steatosis and steatotic liver disease (SLD), is a condition where excess fat builds up in the liver. [1] Often there are no or few symptoms. [1] [2] Occasionally there may be tiredness or pain in the upper right side of the abdomen. [1] Complications may include cirrhosis, liver cancer, and esophageal varices. [1] [3]
The main subtypes of fatty liver disease are metabolic dysfunction–associated steatotic liver disease (MASLD, formerly "non-alcoholic fatty liver disease" (NAFLD)) and alcohol-associated liver disease (ALD), with the category "metabolic and alcohol associated liver disease" (metALD) describing an overlap of the two. [5]
The primary risks include alcohol, type 2 diabetes, and obesity. [1] [3] Other risk factors include certain medications such as glucocorticoids, and hepatitis C. [1] It is unclear why some people with NAFLD develop simple fatty liver and others develop nonalcoholic steatohepatitis (NASH), which is associated with poorer outcomes. [1] Diagnosis is based on the medical history supported by blood tests, medical imaging, and occasionally liver biopsy. [1]
Treatment of NAFLD is generally by dietary changes and exercise to bring about weight loss. [1] In those who are severely affected, liver transplantation may be an option. [1] More than 90% of heavy drinkers develop fatty liver while about 25% develop the more severe alcoholic hepatitis. [4] NAFLD affects about 30% of people in Western countries and 10% of people in Asia. [2] NAFLD affects about 10% of children in the United States. [1] It occurs more often in older people and males. [3] [6]
Fatty liver disease was classified into:
In 2023, a new nomenclature was chosen, [5] [7] with the classifications including:
Often there are no or few symptoms. [1] Occasionally there may be tiredness or pain in the upper right side of the abdomen. [1]
Fatty liver can develop into hepatic fibrosis, cirrhosis or liver cancer. [8] For people affected by NAFLD, the 10-year survival rate was about 80%. The rate of progression of fibrosis is estimated to be one per 7 years in NASH and one per 14 years in NAFLD, with an increasing speed. [9] [10] There is a strong relationship between these pathologies and metabolic illnesses (diabetes type II, metabolic syndrome). These pathologies can also affect non-obese people, who are then at a higher risk. [8]
Less than 10% of people with cirrhotic alcoholic FLD will develop hepatocellular carcinoma, [11] the most common type of primary liver cancer in adults, but up to 45% people with NASH without cirrhosis can develop hepatocellular carcinoma. [12]
The condition is also associated with other diseases that influence fat metabolism. [13]
Fatty liver (FL) is commonly associated with metabolic syndrome (diabetes, hypertension, obesity, and dyslipidemia), but can also be due to any one of many causes: [14] [15]
The fatty change represents the intracytoplasmatic accumulation of triglycerides (neutral fats). At the beginning, the hepatocytes present small fat vacuoles (liposomes) around the nucleus (microvesicular fatty change). In this stage, liver cells are filled with multiple fat droplets that do not displace the centrally located nucleus. In the late stages, the size of the vacuoles increases, pushing the nucleus to the periphery of the cell, giving a characteristic signet ring appearance (macrovesicular fatty change). These vesicles are well-delineated and optically "empty" because fats dissolve during tissue processing. Large vacuoles may coalesce and produce fatty cysts, which are irreversible lesions. Macrovesicular steatosis is the most common form and is typically associated with alcohol, diabetes, obesity, and corticosteroids. Acute fatty liver of pregnancy and Reye's syndrome are examples of severe liver disease caused by microvesicular fatty change. [19] The diagnosis of steatosis is made when fat in the liver exceeds 5–10% by weight. [13] [20] [21]
Defects in fatty acid metabolism are responsible for pathogenesis of FLD, which may be due to imbalance in energy consumption and its combustion, resulting in lipid storage, or can be a consequence of peripheral resistance to insulin, whereby the transport of fatty acids from adipose tissue to the liver is increased. [13] [22] Impairment or inhibition of receptor molecules (PPAR-α, PPAR-γ and SREBP1) that control the enzymes responsible for the oxidation and synthesis of fatty acids appears to contribute to fat accumulation. In addition, alcohol use disorder is known to damage mitochondria and other cellular structures, further impairing cellular energy mechanism. On the other hand, non-alcoholic FLD may begin as excess of unmetabolised energy in liver cells. Hepatic steatosis is considered reversible and to some extent nonprogressive if the underlying cause is reduced or removed.
Severe fatty liver is sometimes accompanied by inflammation, a situation referred to as steatohepatitis. Progression to alcoholic steatohepatitis (ASH) or non-alcoholic steatohepatitis (NASH) depends on the persistence or severity of the inciting cause. Pathological lesions in both conditions are similar. However, the extent of inflammatory response varies widely and does not always correlate with degree of fat accumulation. Steatosis (retention of lipid) and onset of steatohepatitis may represent successive stages in FLD progression. [23]
Liver disease with extensive inflammation and a high degree of steatosis often progresses to more severe forms of the disease. [24] Hepatocyte ballooning and necrosis of varying degrees are often present at this stage. Liver cell death and inflammatory responses lead to the activation of hepatic stellate cells, which play a pivotal role in hepatic fibrosis. The extent of fibrosis varies widely. Perisinusoidal fibrosis is most common, especially in adults, and predominates in zone 3 around the terminal hepatic veins. [25]
The progression to cirrhosis may be influenced by the amount of fat and degree of steatohepatitis and by a variety of other sensitizing factors. In alcoholic FLD, the transition to cirrhosis related to continued alcohol consumption is well-documented, but the process involved in non-alcoholic FLD is less clear.
Flow chart for diagnosis [15] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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‡ Criteria for nonalcoholic fatty liver disease: consumption of ethanol less than 20 g/day for women and 30 g/day for men [26] |
Most individuals are asymptomatic and are usually discovered incidentally because of abnormal liver function tests or hepatomegaly noted in unrelated medical conditions. Elevated liver enzymes are found in as many as 50% of patients with simple steatosis. [27] : 1794 The serum alanine transaminase (ALT) level usually is greater than the aspartate transaminase (AST) level in the nonalcoholic variant and the opposite in alcoholic FLD (AST:ALT more than 2:1). Simple blood tests may help to determine the magnitude of the disease by assessing the degree of liver fibrosis. [28] For example, AST-to-platelets ratio index (APRI score) and several other scores, calculated from the results of blood tests, can detect the degree of liver fibrosis and predict the future formation of liver cancer. [29]
Imaging studies are often obtained during the evaluation process. Ultrasonography reveals a "bright" liver with increased echogenicity. Pocket-sized ultrasound devices might be used as point-of-care screening tools to diagnose liver steatosis. [30] [31] Medical imaging can aid in diagnosis of fatty liver; fatty livers have lower density than spleens on computed tomography (CT), and fat appears bright in T1-weighted magnetic resonance images (MRIs). Magnetic resonance elastography, a variant of magnetic resonance imaging, is investigated as a non-invasive method to diagnose fibrosis progression. [32] Histological diagnosis by liver biopsy is the most accurate measure of fibrosis and liver fat progression as of 2018. [8] Conventional imaging methods, such as ultrasound, CT and MRI, are not specific enough to detect fatty liver disease unless fat occupies at least 30% of the liver volume. [33]
Decreasing caloric intake by at least 30% or by approximately 750–1,000 kcal/day results in improvement in hepatic steatosis. [8] For people with NAFLD or NASH, weight loss via a combination of diet and exercise was shown to improve or resolve the disease. [8] In more serious cases, medications that decrease insulin resistance, hyperlipidemia, and those that induce weight loss such as bariatric surgery as well as vitamin E have been shown to improve or resolve liver function. [8] [15]
Bariatric surgery, while not recommended in 2017 as a treatment for FLD alone, has been shown to revert FLD, NAFLD, NASH and advanced steatohepatitis in over 90% of people who have undergone this surgery for the treatment of obesity. [8] [34]
In the case of long-term total-parenteral-nutrition-induced fatty liver disease, choline has been shown to alleviate symptoms. [35] [36] [37] This may be due to a deficiency in the methionine cycle. [38]
NAFLD affects about 30% of people in Western countries and 10% of people in Asia. [2] In the United States, rates are around 35% with about 7% having the severe form NASH. [1] NAFLD affects about 10% of children in the United States. [1] Recently the term Metabolic dysfunction-associated fatty liver disease (MAFLD) has been proposed to replace NAFLD. MAFLD is a more inclusionary diagnostic name as it is based on the detection of fatty liver by histology (biopsy), medical imaging or blood biomarkers but should be accompanied by either overweight/obesity, type 2 diabetes mellitus, or metabolic dysregulation. [39] The new definition no longer excludes alcohol consumption or coexistence of other liver diseases such as viral hepatitis. Using this more inclusive definition, the global prevalence of MAFLD is an astonishingly high 50.7%. [39] Indeed, also using the old NAFLD definition, the disease is observed in up to 80% of obese people, 35% of whom progress to NASH, [40] and in up to 20% of normal weight people, [10] despite no evidence of excessive alcohol consumption. FLD is the most common cause of abnormal liver function tests in the United States. [14] Fatty liver is more prevalent in Hispanic people than white, with black people having the lowest prevalence. [10]
In the study Children of the 90s, 2.5% born in 1991 and 1992 were found by ultrasound at the age of 18 to have non-alcoholic fatty liver disease; five years later transient elastography found over 20% to have the fatty deposits on the liver, indicating non-alcoholic fatty liver disease; half of those were classified as severe. The scans also found that 2.4% had a degree of liver fibrosis, which can lead to cirrhosis. [41] [42]
After the lockdown of the COVID-19 pandemic, a study demonstrated that 48% of patients with liver steatosis gained weight, while 16% had a worsened steatosis grade. Weight gain was associated with poor adherence to the suggested diet, reduced levels of physical activity, and increased prevalence of homozygosity for the PNPLA3 rs738409 single nucleotide polymorphism. [43] PNPLA3 rs738409 is already a known risk factor for NAFLD. [44] [45]
Fatty liver disease can occur in pets such as reptiles (particularly turtles [46] ) and birds [47] as well as mammals like cats and dogs. [48] The most common cause is overnutrition. A distinct sign in birds is a misshapen beak. Fatty livers can be induced via gavage in geese or ducks to produce foie gras. Fatty liver can also be induced in ruminants such as sheep by a high-caloric diet. [49] [50]
Hepatitis is inflammation of the liver tissue. Some people or animals with hepatitis have no symptoms, whereas others develop yellow discoloration of the skin and whites of the eyes (jaundice), poor appetite, vomiting, tiredness, abdominal pain, and diarrhea. Hepatitis is acute if it resolves within six months, and chronic if it lasts longer than six months. Acute hepatitis can resolve on its own, progress to chronic hepatitis, or (rarely) result in acute liver failure. Chronic hepatitis may progress to scarring of the liver (cirrhosis), liver failure, and liver cancer.
Alcoholic liver disease (ALD), also called alcohol-related liver disease (ARLD), is a term that encompasses the liver manifestations of alcohol overconsumption, including fatty liver, alcoholic hepatitis, and chronic hepatitis with liver fibrosis or cirrhosis.
Steatosis, also called fatty change, is abnormal retention of fat (lipids) within a cell or organ. Steatosis most often affects the liver – the primary organ of lipid metabolism – where the condition is commonly referred to as fatty liver disease. Steatosis can also occur in other organs, including the kidneys, heart, and muscle. When the term is not further specified, it is assumed to refer to the liver.
Alcoholic hepatitis is hepatitis due to excessive intake of alcohol. Patients typically have a history of at least 10 years of heavy alcohol intake, typically 8–10 drinks per day. It is usually found in association with fatty liver, an early stage of alcoholic liver disease, and may contribute to the progression of fibrosis, leading to cirrhosis. Symptoms may present acutely after a large amount of alcoholic intake in a short time period, or after years of excess alcohol intake. Signs and symptoms of alcoholic hepatitis include jaundice, ascites, fatigue and hepatic encephalopathy. Mild cases are self-limiting, but severe cases have a high risk of death. Severity in alcoholic hepatitis is determined several clinical prediction models such as the Maddrey's Discriminant Function and the MELD score.
Liver disease, or hepatic disease, is any of many diseases of the liver. If long-lasting it is termed chronic liver disease. Although the diseases differ in detail, liver diseases often have features in common.
Steatohepatitis is a type of fatty liver disease, characterized by inflammation of the liver with concurrent fat accumulation in liver. Mere deposition of fat in the liver is termed steatosis, and together these constitute fatty liver changes.
Metabolic dysfunction–associated steatotic liver disease (MASLD), previously known as non-alcoholic fatty liver disease (NAFLD), is a type of chronic liver disease. This condition is diagnosed when there is excessive fat build-up in the liver, and at least one metabolic risk factor. When there is also increased alcohol intake, the term MetALD, or metabolic dysfunction and alcohol associated/related liver disease is used, and differentiated from alcohol-related liver disease (ALD) where alcohol is the predominant cause of the steatotic liver disease. The terms non-alcoholic fatty liver (NAFL) and non-alcoholic steatohepatitis have been used to describe different severities, the latter indicating the presence of further liver inflammation. NAFL is less dangerous than NASH and usually does not progress to it, but this progression may eventually lead to complications, such as cirrhosis, liver cancer, liver failure, and cardiovascular disease.
Acute fatty liver of pregnancy is a rare life-threatening complication of pregnancy that occurs in the third trimester or the immediate period after delivery. It is thought to be caused by a disordered metabolism of fatty acids by mitochondria in the fetus, caused by long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency. This leads to decreased metabolism of long chain fatty acids by the feto-placental unit, causing subsequent rise in hepatotoxic fatty acids in maternal plasma. The condition was previously thought to be universally fatal, but aggressive treatment by stabilizing the mother with intravenous fluids and blood products in anticipation of early delivery has improved prognosis.
Phosphatidylethanolamine N-methyltransferase is a transferase enzyme which converts phosphatidylethanolamine (PE) to phosphatidylcholine (PC) in the liver. In humans it is encoded by the PEMT gene within the Smith–Magenis syndrome region on chromosome 17.
Cirrhosis, also known as liver cirrhosis or hepatic cirrhosis, chronic liver failure or chronic hepatic failure and end-stage liver disease, is a condition of the liver in which the normal functioning tissue, or parenchyma, is replaced with scar tissue (fibrosis) and regenerative nodules as a result of chronic liver disease. Damage to the liver leads to repair of liver tissue and subsequent formation of scar tissue. Over time, scar tissue and nodules of regenerating hepatocytes can replace the parenchyma, causing increased resistance to blood flow in the liver's capillaries—the hepatic sinusoids—and consequently portal hypertension, as well as impairment in other aspects of liver function. The disease typically develops slowly over months or years.
Obeticholic acid (OCA), sold under the brand name Ocaliva, is a semi-synthetic bile acid analogue which has the chemical structure 6α-ethyl-chenodeoxycholic acid. It is used as a medication used to treat primary biliary cholangitis. Intercept Pharmaceuticals Inc. hold the worldwide rights to develop OCA outside Japan and China, where it is licensed to Dainippon Sumitomo Pharma.
Aramchol is an investigational drug being developed by Galmed Pharmaceuticals as a first-in-class, potentially disease modifying treatment for nonalcoholic steatohepatitis, or NASH, a more advanced condition of non-alcoholic fatty liver disease.
Christos Socrates Mantzoros is a Greek-born American physician-scientist, practicing internist-endocrinologist, teacher and researcher. He is a professor of medicine at Harvard Medical School and an adjunct professor at Boston University School of Medicine. He currently serves as the chief of endocrinology, diabetes and metabolism at the VA Boston Healthcare System, where he created de novo a leading academic division true to its tripartite mission and as the founding director of human nutrition at Beth Israel Deaconess Medical Center (BIDMC), Harvard Medical School. Finally, he holds the editor-in-chief position of the journal Metabolism: Clinical and Experimental.
Melissa Palmer is an American hepatologist. She is recognized for her research and treatment of hepatitis and liver disease. Palmer is the Chief Medical Officer of Gannex Pharma, a wholly owned company of Ascletis Pharma.
Claudio Tiribelli is an Italian hepatologist best known for his studies on bilirubin and Kernicterus, a bilirubin-induced neurological condition.
Cilofexor is a nonsteroidal farnesoid X receptor (FXR) agonist in clinical trials for the treatment of non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), and primary sclerosing cholangitis (PSC). It is being investigated for use alone or in combination with firsocostat, selonsertib, or semaglutide. In rat models and human clinical trials of NASH it has been shown to reduce fibrosis and steatosis, and in human clinical trials of PSC it improved cholestasis and reduced markers of liver injury.
Hepatokines are proteins produced by liver cells (hepatocytes) that are secreted into the circulation and function as hormones across the organism. Research is mostly focused on hepatokines that play a role in the regulation of metabolic diseases such as diabetes and fatty liver and include: Adropin, ANGPTL4, Fetuin-A, Fetuin-B, FGF-21, Hepassocin, LECT2, RBP4,Selenoprotein P, Sex hormone-binding globulin.
AXA1125 is an experimental drug developed by Axcella Health that "increased β-oxidation and improved bioenergetics in preclinical models". It was studied as a treatment for non-alcoholic fatty liver disease and long COVID.
HU6 is the first Controlled Metabolic Accelerator (CMA). CMAs are designed to increase basal metabolic rate (BMR) by a small, imperceptible amount. The result is a selective increase in fat metabolism and loss of body fat, especially visceral fat. There is also an independent reduction in Reactive Oxygen Species (ROS) or free radicals, thus reducing systemic inflammation. Developed by Rivus Pharmaceuticals, the drug is tested to reduce weight and liver fat in humans with risk factors for metabolic dysfunction-associated steatohepatitis (MASH). In a phase 2a trial, the higher dosage levels reduced liver fat on average by more than 30 percent and also reduced body weight significantly. A phase 2b trial in MASH was subsequently initiated. Data from this study is expected to be reported in 2025. Additionally, a Phase 2a study (HuMAIN) was performed in patients suffering from Heart Failure with Preserved Ejection Fraction (HFpEF), a disease that is mediated by visceral fat and obesity. The study achieved the primary endpoint of weight loss, as well as a number of secondary endpoints.
Nimer Assy is an Israeli hepatologist and academic focusing on internal medicine and liver transplantation. He is a professor at the Bar-Ilan University Azrieli Medical School and the Department Head of the Clinical Research Unit within Internal Medicine Ward A of the Galilee Medical Center.