Hepatitis has a broad spectrum of presentations that range from a complete lack of symptoms to severe liver failure. The acute form of hepatitis, generally caused by viral infection, is characterized by constitutional symptoms that are typically self-limiting. Chronic hepatitis presents similarly, but can manifest signs and symptoms specific to liver dysfunction with long-standing inflammation and damage to the organ.

Acute viral hepatitis follows a pattern of infection that involves three distinct phases:

1. The initial prodromal phase (preceding symptoms) involves non-specific and flu-like symptoms common to many acute viral infections. These include fatigue, nausea, vomiting, poor appetite, joint pain, and headaches. Fever, when present, is most common in cases of hepatitis A and E. Late in this phase, people can experience liver-specific symptoms, including choluria (dark urine) and clay-colored stools.

2. Yellowing of the skin and whites of the eyes follow the prodrome after about 1–2 weeks and can last for up to 4 weeks. The non-specific symptoms seen in the prodromal typically resolve by this time, but people will develop an enlarged liver and right upper abdominal pain or discomfort. 10–20% of people will also experience an enlarged spleen, while some people will also experience a mild unintentional weight loss.

3. The recovery phase is characterized by resolution of the clinical symptoms of hepatitis with persistent elevations in liver lab values and potentially a persistently enlarged liver. All cases of hepatitis A and E are expected to fully resolve after 1–2 months. Most hepatitis B cases are also self-limiting and will resolve in 3–4 months. Few cases of hepatitis C will resolve completely.

Both drug-induced hepatitis and autoimmune hepatitis can present very similarly to acute viral hepatitis, with slight variations in symptoms depending on the cause. Cases of drug-induced hepatitis can manifest with systemic signs of an allergic reaction including rash, fever, serositis (inflammation of membranes lining certain organs), elevated eosinophils (a type of white blood cell), and suppression of bone marrow activity.

There is a rapid onset of clinical signs over the period of 2–7 days, beginning with anorexia, lethargy, and hyperbilirubinemia (icterus and discolored urine). Signs of hepatic encephalopathy (ataxia, blindness, aggression, and coma) and fever can also occur. Other signs include photodermatitis, hemorrhagic diathesis, dependent edema, and colic. The reason for colic is unknown, but is thought to be due to rapid decrease in the size of the liver, and the increased risk of gastric impaction. Rarely, weight loss can occur.

This is quite extensive and includes

- acute infectious hepatitis

- acute mycotoxicosis

- acute pyrrolizidine toxicosis

- acute infectious hepatitis

- acute mycotoxicosis

- haemolytic disease

- hepatotoxins

This may cause fatty liver, hepatitis, fibrosis and sclerosis leading to cirrhosis and finally liver failure.

This includes mostly drug-induced hepatotoxicity, (DILI) which may generate many different patterns over liver disease, including

- cholestasis

- necrosis

- acute hepatitis and chronic hepatitis of different forms,

- cirrhosis

- Effects of Acetaminophen (Tylenol)

- other rare disorders like focal nodular hyperplasia, Hepatic fibrosis, peliosis hepatis and veno-occlusive disease.

Liver damage is part of Reye's syndrome.

Alcoholic liver disease is a term that encompasses the liver manifestations of alcohol overconsumption, including fatty liver, alcoholic hepatitis, and chronic hepatitis with liver fibrosis or cirrhosis.

It is the major cause of liver disease in Western countries. Although steatosis (fatty liver) will develop in any individual who consumes a large quantity of alcoholic beverages over a long period of time, this process is transient and reversible. Of all chronic heavy drinkers, only 15–20% develop hepatitis or cirrhosis, which can occur concomitantly or in succession.

The mechanism behind this is not completely understood. 80% of alcohol passes through the liver to be detoxified. Chronic consumption of alcohol results in the secretion of pro-inflammatory cytokines (TNF-alpha, Interleukin 6 [IL6] and Interleukin 8 [IL8]), oxidative stress, lipid peroxidation, and acetaldehyde toxicity. These factors cause inflammation, apoptosis and eventually fibrosis of liver cells. Why this occurs in only a few individuals is still unclear. Additionally, the liver has tremendous capacity to regenerate and even when 75% of hepatocytes are dead, it continues to function as normal.

In the early stages, patients with ALD exhibits subtle and often no abnormal physical findings. It is usually not until development of advanced liver disease that stigmata of chronic liver disease become apparent. Early ALD is usually discovered during routine health examinations when liver enzyme levels are found to be elevated. These usually reflect alcoholic hepatic steatosis. Microvesicular and macrovesicular steatosis with inflammation are seen in liver biopsy specimens. These histologic features of ALD are indistinguishable from those of nonalcoholic fatty liver disease. Steatosis usually resolves after discontinuation of alcohol use. Continuation of alcohol use will result in a higher risk of progression of liver disease and cirrhosis. In patients with acute alcoholic hepatitis, clinical manifestations include fever, jaundice, hepatomegaly, and possible hepatic decompensation with hepatic encephalopathy, variceal bleeding, and ascites accumulation.Tender hepatomegaly may be present, but abdominal pain is unusual. Occasionally, the patient may be asymptomatic.

Liver failure or hepatic insufficiency is the inability of the liver to perform its normal synthetic and metabolic function as part of normal physiology. Two forms are recognised, acute and chronic. Recently a third form of liver failure known as acute-on-chronic liver failure (ACLF) is increasingly being recognized.

Acute liver failure is defined as "the rapid development of hepatocellular dysfunction, specifically coagulopathy and mental status changes (encephalopathy) in a patient without known prior liver disease".

The disease process is associated with the development of a coagulopathy of liver aetiology, and clinically apparent altered level of consciousness due to hepatic encephalopathy. Several important measures are immediately necessary when the patient presents for medical attention. The diagnosis of acute liver failure is based on physical exam, laboratory findings, patient history, and past medical history to establish mental status changes, coagulopathy, rapidity of onset, and absence of known prior liver disease respectively.

The exact definition of "rapid" is somewhat questionable, and different sub-divisions exist which are based on the time from onset of first hepatic symptoms to onset of encephalopathy. One scheme defines "acute hepatic failure" as the development of encephalopathy within 26 weeks of the onset of any hepatic symptoms. This is sub-divided into "fulminant hepatic failure", which requires onset of encephalopathy within 8 weeks, and "subfulminant", which describes onset of encephalopathy after 8 weeks but before 26 weeks. Another scheme defines "hyperacute" as onset within 7 days, "acute" as onset between 7 and 28 days, and "subacute" as onset between 28 days and 24 weeks.

Acute fatty liver of pregnancy (or hepatic lipidosis of pregnancy) usually manifests in the third trimester of pregnancy, but may occur any time in the second half of pregnancy, or in the puerperium, the period immediately after delivery. On average, the disease presents during the 35th or 36th week of pregnancy. The usual symptoms in the mother are non-specific including nausea, vomiting, anorexia (or lack of desire to eat) and abdominal pain; excessive thirst may be the earliest symptom without overlap with otherwise considered normal pregnancy symptoms; however, jaundice and fever may occur in as many as 70% of patients.

In patients with more severe disease, pre-eclampsia may occur, which involves elevation of blood pressure and accumulation of fluid (termed oedema). This may progress to involvement of additional systems, including acute renal failure, hepatic encephalopathy, and pancreatitis. There have also been reports of diabetes insipidus complicating this condition.

Many laboratory abnormalities are seen in acute fatty liver of pregnancy. Liver enzymes are elevated, with the AST and ALT enzymes ranging from minimal elevation to 1000 IU/L, but usually staying in the 300-500 range. Bilirubin is almost universally elevated. Alkaline phosphatase is often elevated in pregnancy due to production from the placenta, but may be additionally elevated. Other abnormalities may include an elevated white blood cell count, hypoglycemia, elevated coagulation parameters, including the international normalized ratio, and decreased fibrinogen. Frank disseminated intravascular coagulation, or DIC, may occur in as many as 70% of people.

Abdominal ultrasound may show fat deposition in the liver, but, as the hallmark of this condition is microvesicular steatosis (see pathology below), this is not seen on ultrasound. Rarely, the condition can be complicated by rupture or necrosis of the liver, which may be identified by ultrasound.

The main features of acute liver failure are rapid-onset jaundice, weakness, and eventually, changes in mental status that can begin as mild confusion but progress to coma.

The main sign of jaundice is a yellowish discoloration of the white area of the eye and the skin. Urine is dark in colour.

Slight increases in serum bilirubin are best detected by examining the sclerae, which have a particular affinity for bilirubin due to their high elastin content. The presence of scleral icterus indicates a serum bilirubin of at least 3 mg/dL.

The conjunctiva of the eye are one of the first tissues to change color as bilirubin levels rise in jaundice. This is sometimes referred to as "scleral icterus". However, the sclera themselves are not "icteric" (stained with bile pigment) but rather the conjunctival membranes that overlie them. The yellowing of the "white of the eye" is thus more properly termed "conjunctival icterus". The term "icterus" itself is sometimes incorrectly used to refer to jaundice that is noted in the sclera of the eyes; however, its more common and more correct meaning is entirely synonymous with jaundice.

Chemicals produce a wide variety of clinical and pathological hepatic injury. Biochemical markers (e.g. alanine transferase, alkaline phosphatase and bilirubin) are often used to indicate liver damage. Liver injury is defined as a rise in either (a) ALT level more than three times of upper limit of normal (ULN), (b) ALP level more than twice ULN, or (c) total bilirubin level more than twice ULN when associated with increased ALT or ALP. Liver damage is further characterized into hepatocellular (predominantly initial Alanine transferase elevation) and cholestatic (initial alkaline phosphatase rise) types. However they are not mutually exclusive and mixed types of injuries are often encountered.

Specific histo-pathological patterns of liver injury from drug-induced damage are discussed below.

Zonal Necrosis

This is the most common type of drug-induced liver cell necrosis where the injury is largely confined to a particular zone of the liver lobule. It may manifest as a very high level of ALT and severe disturbance of liver function leading to acute liver failure.

Hepatitis

In this pattern, hepatocellular necrosis is associated with infiltration of inflammatory cells. There can be three types of drug-induced hepatitis. (A) viral hepatitis is the most common, where histological features are similar to acute viral hepatitis. (B) in focal or non-specific hepatitis, scattered foci of cell necrosis may accompany lymphocytic infiltration. (C) chronic hepatitis is very similar to autoimmune hepatitis clinically, serologically, and histologically.

Cholestasis

Liver injury leads to impairment of bile flow and cases are predominated by itching and jaundice. Histology may show inflammation (cholestatic hepatitis) or it can be bland (without any parenchymal inflammation). On rare occasions, it can produce features similar to primary biliary cirrhosis due to progressive destruction of small bile ducts (Vanishing duct syndrome).

Steatosis

Hepatotoxicity may manifest as triglyceride accumulation, which leads to either small-droplet (microvesicular) or large-droplet (macrovesicular) fatty liver. There is a separate type of steatosis by which phospholipid accumulation leads to a pattern similar to the diseases with inherited phospholipid metabolism defects (e.g., Tay-Sachs disease)

Granuloma

Drug-induced hepatic granulomas are usually associated with granulomas in other tissues and patients typically have features of systemic vasculitis and hypersensitivity. More than 50 drugs have been implicated.

Vascular lesions

These result from injury to the vascular endothelium.

Neoplasm

Neoplasms have been described with prolonged exposure to some medications or toxins. Hepatocellular carcinoma, angiosarcoma, and liver adenomas are the ones usually reported.

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 mother, caused by long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency. 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.

Hepatotoxicity (from "hepatic toxicity") implies chemical-driven liver damage. Drug-induced liver injury is a cause of acute and chronic liver disease.

The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure the organ. Other chemical agents, such as those used in laboratories and industries, natural chemicals (e.g., microcystins) and herbal remedies can also induce hepatotoxicity. Chemicals that cause liver injury are called hepatotoxins.

More than 900 drugs have been implicated in causing liver injury (see LiverTox, external link, below) and it is the most common reason for a drug to be withdrawn from the market. Hepatotoxicity and drug-induced liver injury also account for a substantial number of compound failures, highlighting the need for drug screening assays, such as stem cell-derived hepatocyte-like cells, that are capable of detecting toxicity early in the drug development process. Chemicals often cause subclinical injury to the liver, which manifests only as abnormal liver enzyme tests.

Drug-induced liver injury is responsible for 5% of all hospital admissions and 50% of all acute liver failures.

"Hepatocellular (hepatic)" jaundice can be caused by acute or chronic hepatitis, hepatotoxicity, cirrhosis, drug-induced hepatitis and alcoholic liver disease. Cell necrosis reduces the liver's ability to metabolize and excrete bilirubin leading to a buildup of unconjugated bilirubin in the blood. Other causes include primary biliary cirrhosis leading to an increase in plasma conjugated bilirubin because there is impairment of excretion of conjugated bilirubin into the bile. The blood contains an abnormally raised amount of conjugated bilirubin and bile salts which are excreted in the urine. Jaundice seen in the newborn, known as "neonatal jaundice", is common in newborns as hepatic machinery for the conjugation and excretion of bilirubin does not fully mature until approximately two weeks of age. Rat fever (leptospirosis) can also cause hepatic jaundice. In hepatic jaundice, there is invariably cholestasis. Defects in bilirubin metabolism also leads to jaundice, as in Gilbert's syndrome (a genetic disorder of bilirubin metabolism which can result in mild jaundice, which is found in about 5% of the population) and Crigler-Najjar syndrome, Type I and II.

Laboratory findings depend on the cause of jaundice.

- Urine: Conjugated bilirubin present, urobilirubin > 2 units but variable (except in children). Kernicterus is a condition not associated with increased conjugated bilirubin.

- Plasma protein show characteristic changes.

- Plasma albumin level is low but plasma globulins are raised due to an increased formation of antibodies.

Bilirubin transport across the hepatocyte may be impaired at any point between the uptake of unconjugated bilirubin into the cell and transport of conjugated bilirubin into biliary canaliculi. In addition, swelling of cells and oedema due to inflammation cause mechanical obstruction of intrahepatic biliary tree. Hence in hepatocellular jaundice, concentration of both unconjugated and conjugated bilirubin rises in the blood. In hepatocellular disease, there is usually interference in all major steps of bilirubin metabolism—uptake, conjugation and excretion. However, excretion is the rate-limiting step, and usually impaired to the greatest extent. As a result, conjugated hyperbilirubinaemia predominates.

The unconjugated bilirubin still enters the liver cells and becomes conjugated in the usual way. This conjugated bilirubin is then returned to the blood, probably by rupture of the congested bile canaliculi and direct emptying of the bile into the lymph leaving the liver. Thus, most of the bilirubin in the plasma becomes the conjugated type rather than the unconjugated type, and this conjugated bilirubin which did not go to intestine to become urobilinogen gives the urine the dark color.

In late pregnancy liver function decreases significantly, which can be easily monitored by blood tests. Early clinical manifestations of ALF in late pregnancy include hypodynamia, decrease in appetite, dark amber urine, deep jaundice, nausea, vomiting, and abdominal distention. Among patients whose deaths were attributed to ALF in late pregnancy, the majority had experienced vaginal deliveries.

Fatty liver (FL) is commonly associated with alcohol or metabolic syndrome (diabetes, hypertension, obesity, and dyslipidemia), but can also be due to any one of many causes:

- Metabolic: abetalipoproteinemia, glycogen storage diseases, Weber–Christian disease, acute fatty liver of pregnancy, lipodystrophy

- Nutritional:malnutrition, total parenteral nutrition, severe weight loss, refeeding syndrome, jejunoileal bypass, gastric bypass, jejunal diverticulosis with bacterial overgrowth

- Drugs and toxins: amiodarone, methotrexate, diltiazem, expired tetracycline, highly active antiretroviral therapy, glucocorticoids, tamoxifen, environmental hepatotoxins (e.g., phosphorus, mushroom poisoning)

- Alcohol: Alcoholism is one of the major causes of fatty liver due to production of toxic metabolites like aldehydes during metabolism of alcohol in the liver. This phenomenon most commonly occurs with chronic alcoholism.

- Other: celiac disease, inflammatory bowel disease, HIV, hepatitis C (especially genotype 3), and alpha 1-antitrypsin deficiency

Fatty liver is a reversible condition wherein large vacuoles of triglyceride fat accumulate in liver cells via the process of steatosis (i.e., abnormal retention of lipids within a cell). Despite having multiple causes, fatty liver can be considered a single disease that occurs worldwide in those with excessive alcohol intake and the obese (with or without effects of insulin resistance). The condition is also associated with other diseases that influence fat metabolism. When this process of fat metabolism is disrupted, the fat can accumulate in the liver in excessive amounts, thus resulting in a fatty liver. It is difficult to distinguish alcoholic FLD, which is part of alcoholic liver disease, from nonalcoholic FLD (NAFLD), and both show microvesicular and macrovesicular fatty changes at different stages.

The accumulation of fat in alcoholic or non-alcoholic steatosis may also be accompanied by a progressive inflammation of the liver (hepatitis), called steatohepatitis. This more severe condition may be termed either alcoholic steatohepatitis or non-alcoholic steatohepatitis (NASH).

Cholestasis is a condition where bile cannot flow from the liver to the duodenum. The two basic distinctions are an obstructive type of cholestasis where there is a mechanical blockage in the duct system that can occur from a gallstone or malignancy, and metabolic types of cholestasis which are disturbances in bile formation that can occur because of genetic defects or acquired as a side effect of many medications.

Possible causes:

- pregnancy

- androgens

- birth control pills

- antibiotics (such as TMP/SMX)

- abdominal mass (e.g. cancer)

- biliary atresia and other pediatric liver diseases

- biliary trauma

- congenital anomalies of the biliary tract

- gallstones

- acute hepatitis

- cystic fibrosis

- intrahepatic cholestasis of pregnancy (obstetric cholestasis)

- primary biliary cirrhosis, an autoimmune disorder

- primary sclerosing cholangitis, associated with inflammatory bowel disease

- some drugs (e.g. flucloxacillin and erythromycin)

Drugs such as gold salts, nitrofurantoin, anabolic steroids, chlorpromazine, prochlorperazine, sulindac, cimetidine, erythromycin, estrogen, and statins can cause cholestasis and may result in damage to the liver.

Subacute sclerosing panencephalitis (SSPE) is a rare and chronic form of progressive brain inflammation caused by a persistent infection with measles virus (which can be a result of a mutation of the virus itself). The condition primarily affects children and young adults. It has been estimated that about 1 in 10,000 people infected with measles will eventually develop SSPE. However, a 2016 study estimated that the rate for babies who contracted measles was as high as 1 in 609. No cure for SSPE exists and the condition is often fatal. However, SSPE can be managed by medication if treatment is started at an early stage. Much of the work on SSPE has been performed by the National Institute of Neurological Disorders and Stroke (NINDS).

SSPE should not be confused with acute disseminated encephalomyelitis which has a similar cause but very different timing and course.

Signs and symptoms depend largely upon the primary lesions giving rise to the condition. In addition to the heart or lung symptoms, there will be a sense of fullness and tenderness in the right hypochondriac region. Gastrointestinal catarrh is usually present, and vomiting of blood may occur. There is usually more or less jaundice. Owing to portal obstruction, ascites occurs, followed later by generalised oedema. The stools are light or clay-colored, and the urine is colored by bile. On palpation, the liver is found enlarged and tender, sometimes extending several inches below the costal margin of the ribs.

Acute: The acute form is a sudden onset of the disease at full-force. Symptoms include high fever, anemia (due to the breakdown of red blood cells), weakness, swelling of the lower abdomen and legs, weak pulse, and irregular heartbeat. The horse may die suddenly.

Subacute: A slower, less severe progression of the disease. Symptoms include recurrent fever, weight loss, an enlarged spleen (felt during a rectal examination), anemia, and swelling of the lower chest, abdominal wall, penile sheath, scrotum, and legs.

Chronic: The horse tires easily and is unsuitable for work. The horse may have a recurrent fever and anemia, and may relapse to the subacute or acute form even several years after the original attack.

A horse may also not appear to have any symptoms, yet still tests positive for EIA antibodies. Such a horse can still pass on the disease. According to most veterinarians, horses diagnosed EIA positive usually do not show any sign of sickness or disease.

EIA may cause abortion in pregnant mares. This may occur at any time during the pregnancy if there is a relapse when the virus enters the blood. Most infected mares will abort, however some give birth to healthy foals. Foals are not necessarily infected.

Studies indicate that there are breeds with a tolerance to EIA.

Recent studies in Brazil on living wild horses have shown that in the Pantanal, about 30% of domesticated and about 5.5% of the wild horses are chronically infected with EIA.