Hepatic Flashcards
True or false: The horse does not have a gall bladder so bile flows freely almost continuously and unconcentrated in a direction opposite to blood.
True
Where are the spaces of Disse and what do they do?
Spaces of Disse lie beneath pores in the endothelial lining of the sinusoids. These connect with lymphatic vessels and freely absorb plasma but not RBCs.
A cleft, lies between the hepatocytes and the cells lining the sinusoids. It contains fluid similar to the composition of blood but does not contain erythrocytes.
What do stellate cells do?
Store fat soluble vitamins such as vitamin A.
What are the different zones of the liver lobule and what are the features of each?
Zone 1 (periportal) is located adjacent to the branching hepatic arteries and portal veins. It is the most oxygenated and hence most metabolically active. Responsible for oxidative liver functions such as gluconeogenesis and ß-oxidation of fatty acids and is the primary site for deposition of haemosiderin.
Zone 2 is the one typically affected by toxins such as creeping indigo.
Zone 3 is located adjacent to the central veins and has the highest cytochrome P450 mixed-function oxidase activity and the least favourable situation for oxygenation. It is most susceptible to toxins and hypoxic damage.
Where does the bile duct empty?
Major duodenal papilla (with the pancreatic duct)
When liver parenchyma cells are destroyed they are replaced with fibrous tissue that eventually contracts around the blood vessels. What is the effect of this?
Portal hypertension which can impede flow from the intestines and spleen resulting in leakage of fluid from the capillaries into the lumen and walls of the the intestine.
Which coagulation and fibrinolysis factors are formed in the liver?
Factors II, V, VII-XIII, fibrinogen, antithrombin III, protein C, plasminogen, plasminogen activatior inhibitor.
What is the role of hepcidin?
Reduces dietary iron absorption by reducing iron transport across the gut mucosa and reduces iron exit from macrophages and the liver.
What influence to glucocorticoids, glucagon and thyroid hormone have on the liver?
They increase gluconeongenesis, glycogenolysis and promote peripheral protein catabolism.
What is the role of the liver in eliminating ammonia?
- Synthesis of non-essential amino acids from α keto acids and ammonia via reversal deamination. Involves formation of glutamate from α-ketoglutarate and ammonia.
- Glutamate is used to form other amino acids and also participates in the conversion of more ammonia into glutamine which is delivered to the kidney to be converted back to ammonia and excreted (glutamine is non-toxic except in the brain where it causes cerebral oedema).
- Ammonia not excreted by the kidneys is returned to the liver where it synthesises urea via the Krebs-Henseleit cycle for excretion via the kidneys.
How are the majority of short-chain fatty acids (SCFA) delivered to the liver?
Incorporated into phospholipid or triglyceride by enterocytes and delivered via the portal blood.
What are the differences between VLDLs and HDLs and what happens to them once packaged?
VLDLs primarily contain triglycerides whereas HDLs primarily contain protein and phospholipids. They are released into hepatic sinusoids and once in the systemic circulation adipose tissue takes them up or endothelial lipases alter their composition by removing triglyceride, forming intermediate low density lipoproteins.
What are the roles of glucocorticoids and insulin on fatty acids in the liver?
Glucocorticoids increase fatty acid mobilisation from the periphery.
Insulin decreases adipose tissue release of fatty acids by activating lipoprotein lipase and inhibiting hormone sensitive lipase.
Insulin also acts on the liver to increase fatty acid synthesis from glucose.
What is the role of bile acids?
Amphoteric molecules that act as detergents to facilitate excretion of cholesterol and phospholipid from the liver into bile and facilitate digestion and absorption of lipid and lipid soluble compounds such as vitamin A, D, E and K from the intestinal tract.
What is the difference between conjugated and unconjugated bilirubin?
Macrophages in the spleen, bone marrow and liver engulf pigments, convert them to biliverdin, and then convert that to bilirubin and release it as free bilirubin - this is unconjugated for which is bound to albumin and delivered to the liver. Within the hepatocyte, the bilirubin is conjugated with glucuronide and is now water soluble and excreted into the bile canaliculi as conjugated bilirubin.
In normal circumstances, little conjugated bilirubin escapes into the circulation but with severe liver disease, increased amounts will escape and be freely filtered in the urine.
Microflora in the GIT reduce conjugated bilirubin to urobilinogen and stercobilinogen which impart a yellow-brown colour to faeces. Urobilinogen is absorbed by intestinal mucosa and returned to the liver.
A small amount of conjugated bilirubin in the intestinal lumen is hydrolysed to unconjugated bilirubin and reabsorbed. The live extracts most of the urobilinogen however a small amount spills over into the urine where it is concentrated and therefore detectable.
What are the phases of hepatic detoxification?
Phase 1: polar groups are added to the compound or existing polar groups are exposed by oxidation, hydroxylation, deamination or reduction. Some substrates are capable of saturating the enzymes responsible for this (usually of the P450 system) causing accelerated removal rates (eg barbiturates, bute, chlorinated hydrocarbons); others are inhibitors of these microsomal enzymes thus prolonging effects (eg chloramphenicol, cimetidine, organophosphates, morphine and quinidine)
Phase 2. The product of phase 1 is conjugated usually with glucuronate or sulphate.
True or false: substances for detoxification are usually water-soluble and biotransformation renders them more susceptible to renal or biliary excretion.
False. Substances for detoxification are usually water INSOLUBLE and biotransformation renders them more susceptible to renal or biliary excretion.
Biotransformation sometimes results in the formation of toxic metabolites from a non-toxic parent compound. Which group of horses may be more at risk of toxic effects when metabolising these compounds?
Young horses may have less ability to metabolise aromatic hydrocarbons for example.
What is the role of Kupffer cells?
They phagocytose and cleans the portal blood of bacterial endotoxins and other products absorbed from the GIT before they reach the systemic circulation and help cleanse the hepatic arterial blood of fibrin degradation products, tissue plasminogen activators, haemoglobin, microbes, foreign antigens and other particulate debris and help recycle iron from senescent or injured RBCs hence they accumulate haemosiderin.
What role does the liver have in vitamin D metabolism or synthesis?
Vitamin D is first converted in the liver to 25-hydroxycholecalciferol and exported to the kidney where it is transformed into 1,25 dihydroxycholecalciferol, the active form.
What role does the liver have in the foetus and how does this change with adulthood?
In the foetus, the liver is a site of haematopoiesis.
In adults it is an extra-medullary site only for intense conditions of erythrocyte regeneration or if a large portion of the bone marrow is destroyed.
In most conditions, what proportion of hepatic mass must be lost before the hepatic function is impaired?
80%+
Why do clinical signs rarely accompany focal hepatic injury?
Because sufficient hepatic reserve exists in unaffected regions to compensate.
The multifocal or generalised disease is more likely to result in clinically significant hepatic disease.
What is bridging necrosis?
Necrosis of contiguous hepatocytes that spans adjacent lobules in a portal to portal, portal to central or central to central fashion.
What are the gross features of zonal injury and common types of zonal injury?
Appears pale with an enhanced lobular pattern on the cut surface. Two most common types of zonal injury are centrilobular (primarily zone 3, such as severe acute anaemia, passive congestion from congestive heart failure and PA toxicity) and peri-acinar (involves only a wedge around the central vein).
Why are centrilobular and peri-acinar hepatocytes most susceptible to anoxic damage?
The normal oxygen tension is lowest in these regions and mixed function oxidase activity is the greatest in these areas.
What is a common cause of periportal (zone 1 acinar lobular) injury?
Infarction of hepatic vessels as may occur with verminous arteritis or exposure to gut-derived toxins.
List causes of acute generalised hepatic injury
- Infection (bacterial, viral, parasitic)
- Necrosis
- Apoptosis
- Inflammation (including immune disorders)
- Hepatotoxic agents
Acute inflammation most commonly accompanies necrosis and is characterised by what cells?
Neutrophils and lymphocytes in the area of cell death or surrounding portal triads.
What is cholangitis and what is the common source?
An inflammatory process primarily involving the biliary system. Usually the result of ascending infection from the GIT after cholestasis.
What role do stellate cells have in hepatic fibrosis and what stimulates them?
Kupffer cells produce TNF-a which stimulates the stellate cells to contract individually but proliferate in number. Once activated, they become chemotactic, decrease their vitamin A stores, secrete collagen and then become senescent.
What conditions commonly result in fibrosis?
Fibrosis often follows conditions resulting in chronic hypoxia, chronic inflammation, chronic cholangitis or cholestasis, metastatic neoplasia, trauma or ingestion of antimitotic agents such as PA.
What are the clinical signs of hepatic insufficiency in horses?
Common: depression, anorexia, colic, HEP, weight loss, orange-coloured urine and icterus.
Less: photosensitization, diarrhoea, bilateral pharyngeal paralysis, bleeding; ascites, dependent oedema;
Rarer: steatorrhea, tenesmus, generalised seborrhea, pruritus, endotoxic shock, polydipsia and haemolysis.
What are the stages (adapted from human medicine) of HEP?
Stage I: mild confusion, decreased attention, slowed ability to perform mental tasks, irritability
Stage II: Drowsiness, lethargy, obvious personality changes, inappropriate behaviour, disorientation
Stage III: Somnolent but rousable, marked confusion, amnesia, occasional aggressive uncontrolled behaviour
Stage IV: Coma
What is the pathogenesis of hepatic encephalopathy and proposed mechanisms?
Several mechanisms may be involved:
- GIT-derived neurotoxins (ammonia most commonly incriminated)
- Augmented activity of GABA
- Altered expression of benzodiazepine receptors
- Increased neurosteroid synthesis
- False neurotransmitter accumulation after plasma amino-acid imbalance (>AAA /
- Increased blood manganese concentrations
- Increase inflammatory mediators expression (cytokines)
- Increased permeability of the BBB and cerebral hypertension
- Impaired CNS energy metabolism.
In the face of liver failure ammonia is insufficiently metabolised via the urea cycle and with increasing concentrations, it enters the CNS and may cause encephalopathy. It has a toxic effect on cell membrane neurons by inhibiting Na/K ATPase activity in nerve cell membranes causing depletion of ATP. It also interferes with CNS energy production through alteration of the tricarboxylic acid cycle resulting in α-ketoglutarate formation and increased synthesis of glutamine which when it accumulates in astrocytes, causes swelling of the cell and generation of cerebral oedema.
Because glutamate is the major excitatory neurotransmitter in the mammalian brain, in acute liver failure increased synaptic release results in overaction of glutamate receptors and hence hyperexcitability. In chronic liver failure downregulation of glutamate receptor activity or increased GABA activity contributes to decreased excitatory transmission. Hyperammonaemia also induces NO and ROS which lead to the accumulation of peroxides, oxidative stress and nerve cell damage. Other gut-derived neurotoxins such as Mercaptans, short-chain fatty acids, oxindole and phenols are likely involved.
Histologically what cell type confirms HEP?
Alzheimer type II changes to astrocytes (enlarge nuclei and lack of cytoplasm).
What mechanisms might induce increased GABAergic tone in HEP?
- Hyperammonaemia may increase GABAergic tone
- The GABA receptor has binding sites for 3 classes of synergistic ligands (GABA and agonists, benzodiazepines, barbiturates); Increased brain levels of natural benzodiazepines may increase GABA-ergic tone in HEP
- There is evidence for a functional increase in GABAergic tone mediated allosterically through the benzodiazepine receptor by an endogenous diazepam-like substance. Clinical response to flumazenil (benzodiazepine receptor antagonist) supports this.
What is the proposed role of inflammatory products associated with hepatic injury in the development of HEP?
- Breakdown products of hepatocytes and inflammatory mediators (cytokines, free radicals etc) increase the permeability of the BBB
- Toxic events in the brain result in both cytotoxic (swelling without alteration in BBB) and vasogenic (increased permeability of the BBB) brain oedema
- TNFα is increased in patients with acute and chronic liver disease and the level correlates with severity of HEP and prognosis.
- TNFα increases ammonia diffusion into the brain, inhibits astrocyte uptake of glutamate and inhibits glutamate synthetase, increases expression of benzodiazepine receptors and increases brain capillary fluid leakage and cerebral oedema formation.
- Excess manganese (as occurs with hepatic disease) potentiates the production of TNFα.
- Alterations in cerebral blood flow and BBB permeability leading to cerebral hypertension and oedema and changes in cerebral metabolism are present in patients with HEP.
What does icterus signify?
Hyperbilirubinaemia
What broad categories cause hyperbilirubinaemia and for each, what are the main causes?
- Increased production: Haemolysis (intra or extravascular) or intracorporeal haemorrhage and subsequent reabsorption of RBC products; Occurs regardless of liver function as the rate of production exceeds the ability of the liver to excrete. Results in increased unconjugated bilirubin, although a mild increase in conjugated bilirubin may occur concurrently.
- Impaired hepatic uptake/conjugation: Results in increased unconjugated bilirubin (retention or hepatic icterus); Most common form in horses. Certain drugs, anorexia or prematurity can impede hepatic uptake and conjugation of bilirubin. Congenital deficiency in enzymes required to conjugate bilirubin may result in ‘Gilbert’s Syndrome’ (human condition, but suspected in some TBs)
- Impaired excretion of bilirubin: Blockage of bile can accompany cholangitis, hepatitis, obstructive cholelithiasis, neoplastic infiltration, fibrosis, physical obstruction of the biliary tract or hyperplasia of the biliary tract. Conjugated >30%.
Is hepatocellular disease most commonly associated with increases in conjugated bilirubin, unconjugated bilirubin or both?
Usually both, although the majority is usually from unconjugated. Increases in the conjugated fraction less than 25% of the total are usually indicative of predominant hepatocellular disease and increases greater than 30% are usually indicative of cholestasis.
Describe the pathogenesis of hepatogenic photosensitisation.
Phylloerythrin is a GIT product of bacterial degradation of chlorophyll that is conjugated and excreted by the liver. During hepatic insufficiency blood concentrations increase. Exposure of the phylloerythrin to UV light causes activation of electrons within the molecule to an excited state, with the resultant free radical formation and cell membrane damage and necrosis.
Unpigmented areas absorb the most UV light hence the lesion distribution. Lesions are initially erythematous and oedematous and progress to pruritus, pain, vesiculation, ulceration, necrosis and sloughing.
Explain why colic might be seen in horses with acute hepatocellular disease?
Pain is due to acute change in hepatic size (due primarily to hepatic swelling) and/or biliary obstruction (cholelithiasis).
Signs may include anorexia, bruxism, dog-sitting, recumbency and rolling.
Palpation on the right, particularly behind the last rib may elicit a pain response.
A proportion (10/25 in one report) of horses with liver disease and colic may also have gastric impactions.
What is the suspected pathogenesis of the development of diarrhoea with hepatic disease, although uncommon?
Alterations in the intestinal microflora, portal hypertension (rare but can increase hydrostatic and oncotic pressure resulting in water and protein loss into the lumen), intestinal hyperema, and deficiency of bile acids may be involved.
Why is steatorrhea rare in horses with hepatic disease?
Due to the low-fat equine diet.
Which factors associated with coagulation and fibrinolysis are sensitive to hepatic disease and why?
- Fibrinogen
- Vitamin K dependent factors (II, VII, IX, X and protein C) have short half-lives. Factor VII half-life is 4-5hours; others range from 4-5 days.
- Vitamin K is fat-soluble so requires bile acids for intestinal absorption, hence any disorder that results in reduced bile acid excretion will limit Vitamin K dependent factors.
- Antithrombin III activity should be increased with liver disease, hence promoting bleeding.
- Failure to remove activated coagulation factors promotes coagulation, and FDP’s interfere with platelet function and fibrin clot formation
What causes pruritus and seborrhea in horses with liver disease?
Retention of bile acids and accumulation in the skin.
True or false: Ponies with hyperlipaemia may develop dependent abdominal oedema after vascular thrombosis or as a result of increased blood flow and hydrostatic pressure in the subcutaneous abdominal vein caused by a partial obstruction of the caudal vena cava by the rapidly enlarged liver
True
Why is oedema secondary to hypoalbuminaemia a rare finding in horses with acute hepatic disease?
The half life of albumin is long (19-20 days) hence hypoalbuminaemia and resultant oedema is rare in acute disease.
What is hepatorenal syndrome?
Acute azotaemia and anuria occur in ponies with hyperlipaemia and hepatic lipidosis. Thought to be due to reduced effective circulating volume, decreased hepatic inactivation of renin and endotoxaemia.
What is the proposed mechanism of PU/PD in cases of chronic hepatic disease?
- Increased aldosterone concentrations occur due to reduced hepatic biotransformation and decreased effective circulating volume due to portal hypertension and hypoalbuminaemia, resulting in Na and H20 retention.
- Na raises osmolality of the extracellular fluid, thereby stimulating the thirst centre and PD/PU ensues.
List the hepatocellular derived enzymes, biliary derived enzymes and indicators of hepatic function.
Hepatocellular enzymes: sorbitol dehydrogenase (SDH), AST, GLDH, ARG, ALP (more biliary, mild hepatocellular), LDH, ALT, ICD
Biliary enzymes: GGT, ALP
Hepatic function: Bile acids, conjugated bilirubin, ammonia, partial thromboplastin time, prothrombin time
True or false: magnitude of elevation of hepatocellular-derived enzymes may not correspond to functional abnormalities and therefore should be interpreted as a measure of disease rather than a test of function
True
List non-hepatic causes of increased unconjugated bilirubin.
- Haemolysis (up to 1,368umol/L)
- Anorexia (up to 135umol/L)
- Intestinal obstruction
- Cardiac insufficiency
- Gilbert’s syndrome (inherited bilirubin-uridine diphosphate glucuronyl transferase deficiency)
- Drug administration (corticosteroids, heparin, halothane)
What is the proposed mechanism for higher bilirubin concentration in foals?
Turnover of foetal haemoglobin to adult haemoglobin and concurrent deficiency of liver-binding and conjugating enzymes relative to adults.
True or false: a normal bilirubin value precludes a diagnosis of hepatic insufficiency.
False.
In a horse with detectable urinary bilirubin concentrations, is a hepatocellular or cholestatic disease more likely and why?
Chlolestatic.
Conjugated bilirubin is water soluble but only excreted in the urine when it reaches levels that surpass the renal threshold. If conjugated bilirubin is contributing more than 30% to the total bilirubin then cholestatic disease is suspected, hence when the value increases sufficiently to cause renal overflow, cholestatic disease should also be suspected
Is detection or failure to detect urobilinogen in urine an indicator of reduced bilirubin excretion?
Failure to detect urobilinogen - this is usually present in urine and indicates a patent bile duct.
True or false: enterohepatic circulation normally removes greater than 90% of bile acids, hence increased concentrations can occur with liver disease and quantitation provides an excellent screen of liver failure
True
True or false: prolonged fasting does not cause an increase in serum bile acids.
False. Short term (<14hrs) doesn’t, but more prolonged fasting does.
List causes for increased bile acids in liver disease
- Shunting or decreased blood flow to the liver (first-pass effect),
- Failure of the liver to remove bile acids from the enterohepatic circulation,
- Failure of hepatocytes to conjugate the bile acids for excretion,
- Failure of excretion and subsequent regurgitation into the blood with biliary obstruction.
In horses with PA toxicity, a serum bile acids above what level was associated with a grave prognosis?
50umol/L
True or false: serum bile acid concentrations are often lower in neonatal foals during the first month of life
False. They are usually higher in foals during the first month of life and frequently exceed 20umol/L.
Which two conditions are typically associated with the highest bile acid concentrations?
Biliary obstructive disease
Portosystemic shunts
Why are globulins often increased with chronic hepatic disease?
Decreased Kupffer cell mass and hence reduced function results in wider dissemination of enteric-derived foreign antigens. Plasma cells respond to the general increased antigen load, resulting in polyclonal gammopathy (α and ß globulin may increase). However, this is of course non-specific.
What are the collection, storage and handling requirements of blood for measurement of ammonia levels?
- EDTA blood can be refrigerated anaerobically for up to 6 hours without a significant increase in ammonia content
- If longer periods before measurement it should be anaerobic collection, prompt removal of RBCs and the plasma sample frozen until measurement.
Is hyperammonaemia a sensitive or specific (or both) indicator of liver dysfunction?
It is a sensitive indicator of liver dysfunction, but not specific for liver disease.
When evaluating clotting factors in liver disease, which is the first that is likely to be abnormal and why?
Abnormalities in prothrombin time (PT) generally occur first due to the short half-life of factor VII.
However to adequately evaluate heamostatic function measurement of activated partial thromboplastin time (APTT), fibrinogen and FDP concentrations and platelet count is required.
What ratio of clotting time (PT or APTT) of the patient with suspected hepatic disease to the normal horse’s value would make you suspect it to be abnormal?
Ratio greater than 1.3
What are the common changes in glucose dynamics with hepatic insufficiency?
Hyperglycaemia can occur secondary to catecholamine and corticosteroid release
Hypoglycaemia can occur secondary to acute massive hepatic failure but is more common with chronic failure because anorexia results in depletion of glycogen stores, and gluconeogenesis and glycogenolysis are impaired by increased glucagon concentrations.
Why might the concentration of triglycerides increase during hepatic insufficiency?
Due to increased mobilisation from adipose tissue to support energy-requiring processes along with decreased clearance by the liver.
Which cytosolic enzymes are liver-specific and not inducible?
And which general liver enzymes are not liver-specific?.
Liver specific:
- Sorbitol dehydrogenase (SDH)
- Arginase (ARG)
- Ornithine carbamoyltransferase
- Glutamate dehydrogenase (GLDH)
Non-specific:
- Aspartate aminotransferase (AST)
- Alkaline phosphatase (ALP)
- Lactate dehydrogenase (LDH) (unless iso-enzyme 5 identified, as this is narrowed to liver and muscle only)
- Alanine aminotransferase (ALT)
- Isocitrate dehydrogenase (ICD)
Why is sorbitol dehydrogenase (SDH) both an ideal and unsuitable candidate for evaluation of acute liver disease?
- Liver specific and not inducible,
- Short half-life makes it ideal for evaluation of acute ongoing disease,
- Returns to baseline within 3-5 days after a transient insult,
- However, the short half-life means it has to be assayed within hours of collection, making it often impractical.
What is the normal half-life of Bromsulphthalein (BSP) in horses, why and how is this measured and what does a prolonged half-life measurement indicate?
Normal half-life is 2.8-0.5min.
It can be measured as a determinant of hepatic function. After IV injection of 2.2mg/kg BSP heparinised samples are taken at 3,6,9,12 and 15 minutes to determine the half-life. If it is prolonged, it suggests a loss of >50% hepatic function. It can hence be used to differentiate HEP from other causes of abnormal behaviour or cerebral signs, or with chronic disease when other enzymes may be normal.
It is probably only available in research settings - clearance of radiopharmaceutical technetium may be more suitable.
What factors may influence the measured half-life of BSP?
- Hypoalbuminaemia results in reduced protein binding so increased delivery to the hepatocyte and shorter half-life.
- Hyperbilirubinaemia will result in competition with bilirubin for binding sites and a prolonged half-life
- With portosystemic shunts, the rate of delivery to the liver will be decreased and the half-life prolonged
What is the procedure for operative mesenteric portography and under what situation is this mostly used in the horse?
A celiotomy is performed, radiopaque material is injected into a mesenteric vein and rapid sequential survey radiographs are obtained. Simultaneous opacification of the portal vein, azygous vein and caudal vena cava or lack of filling of the intrahepatic portal system is indicative of portosystemic shunting.
What sedatives are most safe in cases of HEP?
Xylazine or detomidine
Why is diazepam contraindicated in cases of HEP?
It enhances the effect of GABA on central inhibitory neurons and may exacerbate signs of HEP.
Why might treatment with K and acidifying fluids be useful in some cases of HEP?
Hypokalaemia and alkalosis result in increased renal production of ammonia and increased diffusion of ammonia into the CNS.
Are low protein diets recommended for horses with hepatic disease?
Low protein diets are advisable in patients with hepatic disease causing high blood ammonia and/or signs of HEP. However, a moderate-normal protein diet should be given to horses with chronic liver disease that have normal mentation and blood ammonia concentrations.
List treatment for hepatic disease in horses
In acute disease with HE:
- IVFT, correction of A/B and electrolyte derangement (mild hypokalaemia and/or acidosis may be beneficial for reduced renal ammonia production)
- Lactulose or Lactitol to reduce intestinal ammonia production
- MgSO4 for neuro function
- NSAIDs
- Pentoxifylline to reduce hepatic fibrosis
- Silybin (milk thistle extract) may help with anti-fibrosis, antioxidant and metabolic effects
- Hypertonic saline / mannitol for cerebral oedema
In cholestatic disease:
- Ursodiol may help reduce obstruction by making bile more liquid and easier to excrete
- Vitamin K therapy to reduce risk of deficiency
Describe the pathogenesis of Theiler’s disease
Acute onset, rapidly progressive (2-7days) hepatic failure in adult horses that results initially in anorexia, icterus, progression to HEP, photodermatitis, haemorrhagic diathesis, fever, dependent oedema, bilirubinuria and sudden death in some cases.
Frequently there is a history of previous administration of an equine-origin biologic antiserum 4-10wks prior to onset of signs (AHS, Anthrax, EEE, WEE, tetanus, C. perfringens, C. botulinum, S. equi equi, EHV-1, pregnant mares serum and plasma), with tetanus antitoxin being the most commonly associated (although possibly most frequently used?). In the absence of a history of blood products, seasonality around summer and fall has been reported. Horses that survive more than 1 week usually recover, although sudden death or progressive weight loss can occur.
List clinicopathologic findings and treatment with Theiler’s disease
Clinicopathologic:
- Bilirubinaemia (both conjugated [usually less than 25%] and unconjugated)
- Elevation in liver enzymes SDH, GLDH, ARG and AST
- GGT is elevated but not as high as hepatocellular enzymes
- BSP half-life, PT and APTT are prolonged
- Elevation in blood ammonia is common
Treatment: No specific treatment, Supportive care as if for hepatic insufficiency
List histologic findings with Theiler’s disease
- Small liver
- Widespread centrilobular to mid-zonal hepatocellular necrosis and apoptosis with haemorrhage
- Mod-severe centrilobular hepatocyte vacuolar (fatty) change and granular swelling, haemosiderosis and bile casts.
What is Nonprimate Hepacivirus and what is the prevalence of seropositivity and disease among horses?
Hepacivirus (Flavivirus): Experimental infection results in mild elevations in liver enzymes and lymphocytic portal inflammation and piecemeal hepatocyte necrosis. Enzyme increase is correlated with development of antibodies, suggesting anti-body mediated activity related to the virus could cause clinical disease (SCID foals produce no antibody and have no clinical signs).
- 40% adult horses are seropositive
- 4% prevalence of active infection of which a fifth are chronic carriers
What is Theiler’s disease-associated virus and what are the common findings?
Flavivirus that has been associated with disease in horses that received botulinum antitoxin consisting of clinical and or biochemical evidence of hepatitis 6-8wks after the antitoxin administration. Persistent viraemia was present in 4/17 horses. Horse-horse transmission seems not to occur.
What is Equine Pegivirus?
This flavivirus was identified in horses that showed elevated liver enzymes but were not clinically unwell. The virus has not been shown to be hepatotrophic. Carrier states seem to occur and transmission is thought to be blood although high seroprevalence of the disease suggests transmission other than in plasma and anti-toxin inoculations must occur.
What is equine parvovirus?
This virus has been found in conjunction with Theiler’s disease in horses administered blood-origin products. Experimental inoculation causes liver disease - it is thought to be the most closely associated with Theiler’s disease. Some healthy horses remain persistently viraemic and antibody positive
What is the aetiologic agent, signalment and prognosis in cases of Tyzzer’s disease?
- Clostridium piliforme (motile, spore forming obligate intracytoplasmic bacterium) that is common in the environment (excrete in faeces of healthy foals and mares)
- Foals eat contaminated faeces or soil, the bacteria replicate in the intestinal epithelium and reach the liver and heart by way of the lymphatics and blood supply causing multifocal hepatitis, myocarditis and enteritis.
- Occurs in foals primarily from 7-42 days of age that are often well-grown and otherwise healthy.
- Prognosis is poor - highly fatal.
- Rare reports of treatment with penicillin, TMS and PPN exist but many don’t have definitive diagnosis of the bacterium.
What are the clinical and necropsy findings with Tyzzer’s disease?
Clinically:
- Depression progressing to recumbency, fever, tachypnoea, tachycardia, icterus, petechiation, diarrhoea, dehydration, shock, seizure, coma
- Sudden death with no premonitory signs
Necropsy:
- Swollen liver
- White foci scattered throughout the parenchyma
- Icterus & petechial haemorrhages
- Bacteria may be seen with Warthin-Starry or Dietrerlis-silver stain as haystacks of rods.
List differential diagnoses for Tyzzer’s disease in young foals.
- Iron hepatotoxicity
- Perinatal EHV-1
- Leptospirosis
- Listeria monocytogenes
- Bartonella sp
- Bacteraemia with secondary hepatitis
- Atresia of the bile duct
- Portosystemic shunt
What is the infectious organism and clinical findings of Infectious necrotic hepatitis or black’s disease?
Clostridium novyi type B
- Peracute onset (sometimes with sudden death) and progressive clinical signs over 24-72hrs
- Depression, Reluctance to move, Fever, Icterus, Ataxia, Colic, Petechiae, Periods of recumbency, Tachycardia and tachypnoea.
- May be geographically close to populations of sheep
- Hepatic parasite migration may predispose
- Carcass blackens rapidly after death from engorgement of subcutaneous blood vessels
- Serosanguinous effusion at necropsy
- Widespread haemorrhages and icterus
- Multifocal areas of coagulative hepatic necrosis
- Large numbers of gram-positive rods
- The organism is difficult to isolate, requires rapid tissue sampling and anaerobic conditions.
- High doses of penicillin may be effective, but most cases are fatal.
True or false: neonatal foals infected with EHV-1 typically show profound hepatic necrosis despite serum enzyme activities not significantly different from premature foals or foals with septicaemia.
True.
True or false: icterus in cases of equine infectious anaemia is due to both erythrocyte destruction and acute hepatic necrosis.
True
What are the histological findings of giant cell hepatopathy, in what gestation foetus does it typically occur and what are the suspected aetiological agents?
Disorganisation of hepatic cords, multifocal necrosis, a mild mononuclear cell infiltrates and a large hepatocyte syncytium with 8-10 nuclei.
Occurs in mid-term aborted foetuses
Unknown aetiology but may be due to viral or bacterial infections, including leptospirosis.
List parasitic damage that may be seen in the liver.
- P. equorum - larval migration can cause focal or diffuse hepatic fibrosis
- Strongylus spp - migrate through portal veins causing focal hepatitis, subcapsular haemorrhage and oedema and parenchyma fibrosis with capsular fibrin deposits; S. vulgaris may cause thrombotic emboli and infarcts.
- Echinococcus, Schistosoma and Sarcocystis spp may induce damage by cysts formation and / granuloma.
- Fasciola hepatica - migration and biliary system colonization - cholangiohepatitis.
- Heterobilharzia americana causes a remarkable starry sky image of the liver on ultrasound.
Hepatotoxic chemicals, including arsenic, carbon tetrachloride, chlorinated hydrocarbons in insecticides, carbon disulfide, pentachlorophenols in wood preservatives, phenol disinfectants etc all cause what main pathological findings in the liver with toxicosis?
Centrilobular necrosis
Which drugs can cause adverse liver effects?
Phenothiazines and macrolide antibiotics (cholestatic injury)
Imidocarb (hepatic disease in donkeys only)
Tetracycline (fatty infiltration without dysfunction)
Erythromycin, rifampin, tetracycline, halothane, dantrolene, aspirin, phenobabital (can cause idiosyncratic hepatotoxicity).
Why is prior administration of colostrum somewhat protective against ferrous fumarate iron toxicity in neonates?
Colostrum contains abundant Vit E and essential cofactors for glutathione which protects against free-radical damage which is a proposed mechanism for iron toxicity.
What are the clinical signs and necropsy findings of iron toxicity in foals?
Clinically: HEP, icterus and per-acute death.
Necropsy:
- Small liver with marked hepatic necrosis with blood-filled reticular
- Mild biliary hyperplasia and periportal fibrosis
- Periportal fibrosis
- Alzheimer type 2 cells in the brain (could occur within 48 hours of toxin administration).
What is the mechanism of hepatic failure in foals with neonatal isoerythrolysis (NIE)?
The provision of multiple transfusions of red blood cells adds to the iron overload that is already occurring due to the mass breakdown of their own RBCs. Results in iron toxicity and subsequent liver failure.
Histology shows hepatocellular necrosis with extensive biliary proliferation.
*Note: foals with NI should be given blood transfusions, however, aim for an acceptable level of oxygenation rather than desired PCV to reduce the provision of excessive RBCs that will later contribute to iron overload and potential toxicity.
What is haemochromatosis and what are the features?
Tissue damage and dysfunction caused by deposition of haemosiderin in parenchyma cells.
Excessive dietary iron was not evident in 3 cases. Clinical signs and laboratory evidence of liver disease develop although serum iron was normal in 3 cases. Haemochromatosis was accompanied by bile duct hyperplasia and hepatic fibrosis. All 3 died or were euthanised.
1 case of haemochromatosis associated with excessive dietary iron and increased serum iron is reported.
What is the most common mycotoxin to cause hepatic disease in horses and what are the typical findings?
Fumonisins B (Fusarium). In addition to leukoencephalomalacia this can cause hepatotoxicity with hepatocyte vacuolation with centrilobular fatty change, hepatocyte necrosis, mild mononuclear infiltrate, mild bile duct proliferation and periportal fibrosis.
The complex mechanism of action of Fumonisins B is based on the inhibition of sphingosine (sphinganine) N-acetyltransferase (ceramide synthase)
What other mycotoxins have been associated sporadically with hepatic disease?
Aflatoxins can cause severe illness and death although response to these is variable.
What are the clinical signs of acute biliary occlusion and likely causes?
Icterus and increased conjugated bilirubin, GGT and SBA.
Abdominal pain
Often secondary to cholelithiasis, can be GIT disease such as colon displacement, can be with liver lobe torsion as well as duodenal ulcers in foals, neoplasias and pancreatitis can be associated.
Differentiate hyperlipaemia and hyperlipidaemia
Hyperlipaemia: serum TGL >5.7mmol/L with grossly lipaemic serum; may lead to hepatic fatty infiltration, often accompanied by clinical signs of liver disease and guarded prognosis.
Hyperlipidaemia: serum TGL increased but usually <5.7mmol/L without grossly lipaemic serum or fatty infiltration of the liver.
What are the most common primary diseases predisposing to hyperlipaemia?
- Enterocolitis
- Endotoxemia
- Parasitism
- PPID
- Azotemia
- Neonatal septicemia
List clinical signs of hyperlipaemia
Icterus, anorexia, weakness, severe depression, ataxia, muscular weakness, recumbency, diarrhoea, mild colic, fever, dependent oedema.
Signs of hepatic failure may prevail.
Sudden death with hepatic rupture can occur.
What is the pathogenesis of hyperlipaemia?
When glycogen stores become depleted fatty acid oxidation becomes the main mechanism for energy provision.
Stress increases catecholamines and glucocorticoids which stimulate fatty acid release from adipose tissue. A negative energy balance further promotes fatty acid mobilisation. FFA, non-esterified fatty acids and glycerol are released into the blood and carried to the liver where FFA may be oxidised to ACoA and used for ATP production, re-synthesised into TGLs and stored in the liver or used to make VLDLs. Ponies with hyperlipaemia have larger-diameter VLDLs containing greater concentrations of TGLs. Hence hyperlipaemia in ponies is the result of efficient and excessive hepatic synthesis of TGLs from mobilised FFA with subsequent secretion of TGL laden VLDL into the blood. In addition, activity of lipoprotein lipase is not impaired in these ponies, in fact it is increased. Hence it is the overproduction of VLDLs by the liver, not impairment of their removal which is primarily responsible for hyperlipidaemia in ponies. However, if FFA mobilisation exceeds oxidation and VLDL secretion, hepatic lipidosis ensues and may lead to hepatic failure and/or rupture.
How does insulin normally protect against hyperlipaemia?
Insulin inhibits tissue hormone-sensitive lipase, the enzyme responsible for lipolysis of adipose tissue.
In addition, it stimulates gluconeogenesis in the liver and activates lipoprotein lipase which is responsible for uptake of VLDL by adipose tissue. This mechanism may fail with reduced tissue sensitivity to insulin.
What dietary manipulations should be made in cases of hyperlipaemia?
Concentrated carbohydrate feed such as molasses-coated grain and high-quality pasture or hay should be encouraged. 5% dextrose as a CRI of 2mL/kg/hr and enteral nutrition should be attempted. Avoid fats.
What additional treatment can be implemented to reduce TGL concentrations?
Heparin potentiates the activity of lipoprotein lipase and may increase TG removal from the blood, although in some ponies lipoprotein lipase is already at maximum so the heparin may not provide additional benefit and may increase the risk of haemorrhage.
True or false: ingestion of pyrrolizidine alkaloids typically results in an acute onset liver failure
False. Typically results in a delayed onset, chronic, progressive liver failure.
Acute severe intoxication can produce centrilobular hepatocellular necrosis.
What are the clinical signs of PA toxicity?
- Often delayed by 1-12 months from ingestion
- Anorexia
- Weight loss
- Exercise intolerance
- Mild-moderate icterus
- Oedema
- Diarrhoea
- PU/PD
- Laryngeal paresis
- Oral ulcers +/- halitosis
- Development of HEP and photosensitisation is typically abrupt and late in the disease.
Under which circumstances are horses more likely to eat PA containing plants?
- When no alternative is available.
- If treated with a herbicide (may make them more palatable - often sweeter).
- Contamination of hay or concentrates with PA containing plants.
What is the approximate amount required for PA toxicity?
Consumption of 2-5% body weight in the plants in a short period of time can result in acute toxicity.
However, in most cases, it is the cumulative effect of chronic low-level exposure.
What is the pathogenesis of PA toxicity?
Once ingested, PAs are carried to the liver via the portal circulation and metabolised by microsomal enzymes in zone 3 to toxic pyrrole derivatives. The pyrroles inhibit cellular replication and protein synthesis. Because the cells can’t divide they enlarge and form megalocytes, which then fibrosis when these cells die.
When fibrosis becomes extensive the liver shrinks, develop a firm texture and failure is inevitable. If ingestion has been acute and high volume, extensive centrilobular hepatocellular necrosis occurs and lesions may look similar to Theiler’s disease. It may take 30 days or more to see megalocytes after exposure to PAs.
What extrahepatic effects can be seen with PA toxicity?
- Myocardial necrosis
- Colitis
- Widespread haemorrhages
- Adrenal cortical hypertrophy
- Pulmonary dysfunction includes hydrothorax, pulmonary oedema, epithelialisation and pulmonary arteritis.
Which liver enzymes and at which stages of the disease may be elevated with PA toxicity and why?
During the early disease stage, SDH and AST are often elevated, as well as sometimes GGT and ALP.
During chronic or late stages SDH and AST are often normal or only mildly increased. GGT, ALP and serum bile acids will be persistently increased due to periportal fibrosis.
What is the prognosis for horses with PA toxicity and what is a good measure of subclinical disease in herd-mates?
After onset of clinical signs of liver failure death usually occurs within 10 days.
Serum bile acid >50umol/L is suggestive of a poor prognosis.
GGT may be useful for monitoring in herd-mates.
What are the clinical findings with Alsike Clover and how do you differentiate it from PA toxicity?
Toxic principle unknown - may be the clover or a mycotoxin by a commensal fungus on the plant.
Photodermatitis and liver disease develop after 2 weeks of consumption when the diet consists of at least 20% clover.
Histologically you see biliary hyperplasia and periportal fibrosis without severe bile obstruction.
Typically there are only minimal parenchymal lesions which may distinguish this condition from PA toxicity.
What is chronic active hepatitis and what are the clinical signs?
Chronic progressive hepatopathy characterised by biliary hyperplasia, periportal and/or biliary inflammation and associated hepatocellular damage.
Clinical signs are often insidious and compatible with progressive liver failure (depression, anorexia, weight loss, exercise intolerance, colic, icterus and in many cases fever); may moist exfoliative coronary dermatitis.
What is the pathogenesis of chronic active hepatitis and how is it diagnosed?
Unknown aetiology. A similar condition in humans has been associated with autoimmune diseases and viruses.
Predominantly plasma and mononuclear cells infiltrate the liver of these horses, as well as often concurrent coronary dermatitis, would support autoimmune disease but not proven. Suppurative inflammatory response of the biliary system, periportal inflammation and hepatocellular necrosis would support ascending infection from the GIT.
Mild elevation in SDH and AST alongside marked elevation in GGT and ALP, with or without elevation in bile acids, bilirubin and total protein are suggestive. Definitive diagnosis requires histology to show progressive periportal hepatocellular necrosis that obscures and distorts the limiting plate (cord of hepatocytes that surrounds the portal triad). Bridging fibrosis develops with progression and cirrhosis prevails.
What is the treatment for chronic active hepatitis?
- Corticosteroids may be effective in some cases and may help reduce fibrosis although are unlikely to alter prognosis or long term survival.
- Azathioprine has been used successfully in people but bioavailability in horses is poor.
- Antimicrobials are indicated if the biopsy is suggestive of cholangitis - choose those excreted in bile such as chloramphenicol, ceftiofur, ampicillin, penicillin, gentamicin.
What is the suggested aetiology/pathogenesis for cholelithiasis?
Retrograde bacterial (and potentially ingesta) infection from the small intestine. In some cases, a previous history of enteritis may be present and supports this pathogenesis. The stones tend to be calcium bilirubinate and to a lesser extent calcium phosphate.
It is thought that the calcium bilirubinate crystals form first, followed by sludge formation and then stone formation. If the stones occur in the common bile duct, obstructive failure would be expected.
List clinical signs associated with cholelithiasis/cholangiohepatitis.
- Fever
- Colic
- Icterus
- Weight loss
- Liver enlargement
- Distended, thickened bile ducts with variable liver echogenicity +/- visible calculi.
Often hepatocellular function is not severely compromised due to the acute nature (only mild increase in SDH, GLDH and AST), however, hepatobiliary enzymes are often increased (GGT and ALP as well bilirubin - conjugate fraction >25%).
List the treatments for cholangiohepatitis and cholelithiasis?
- Long term antibiotics (need good gram-ve activity eg enrofloxacin, 3rd gen cephalosporins, aminoglycosides, possible TMS)
- DMSO may be useful for calcium bilirubinate stones as it dissolves the stone
- Ursodiol has no effect in horses on calcium bilirubinate calculi but as an anti-inflammatory and choleretic agent, it increases bile production and may make bile more liquid and easier to excrete.
- Manual crushing or surgical removal may be possible for calculi in the bile duct but intrahepatic calculi are inaccessible.
True or false: Biliary obstruction may be seen in neonatal foals associated with duodenal ulcers adjacent to the hepatopancreatic ampulla, causing biliary stenosis or cholestasis.
True.
True or false: Hepatic abscessation in foals is often haematogenous in origin as sequelae to bacteraemia or ascending through the umbilical vein as sequelae to omphalophlebitis. However, in adults, it is more commonly secondary to ascending infection via the bile duct or from the portal blood.
True.
List the common hepatic neoplasms
- Cholangiocarcinoma (most common)
- Hepatocellular carcinoma / Hepatoma
- Hepatoblastoma
- Mixed hamartoma
What is the origin of Cholangiocarcinoma?
Originates from the bile duct epithelium and has a tendency to form multiple foci, has a firm texture and a whitish colour produced by abundant fibrous stroma.
Primary mass is typically solitary with multiple intrahepatic secondaries.
Extrahepatic metastasis is common, with transperitoneal lymphatic spread to the peritoneum and diaphragm and haematogenous spread to the lungs.
What is amyloidosis and what are the common predisposing conditions?
Extracellular deposition of beta-pleated sheets of AA fibrils (most commonly) distorts normal tissue architecture and may lead to functional impairment. The liver and spleen are the most common organs.
Most affected horses have been hyperimmunised (eg for serum production), have severe parasitism or chronic infection or inflammation.
What are the histological findings with amyloidosis?
Extracellular deposits of AA amyloid periportally and adjacent to the sinusoids in the space of Disse. Often accompanied by hepatocytic atrophy and mild mononuclear cell infiltrate.
What is the difference between systemic primary, immunocytic or idiopathic amyloidosis compared with local immunocytic amyloidosis?
Systemic primary, immunocytic or idiopathic amyloidosis is caused by the deposition of amyloid light-chain fibrils. Green birefringence in polarized light (red congo stain) which lost after treatment whit K permanganate.
Local immunocytic amyloidosis is deposition in the URT mucosa or skin and is more common in horses than systemic primary amyloidosis.
What is the cause of hypoxaemia and pressure necrosis with right-sided heart failure?
Rising pressure in the caudal vena cava and retrograde pressure increases in the hepatic central veins, causing pressure necrosis and hypoxaemia of the adjacent hepatocytes.
What is the typical age of presentation for portosystemic shunts and what is the suggested reason for this delayed presentation?
Typically 2-6mo.
Possibly due to delayed hindgut development in foals - the hindgut is necessary to produce enough enteric ammonia to cause hyperammonaemia and clinical signs.
What are the clinicopathological and histological findings with portosystemic shunts?
Reduced BUN, increased ammonia, increased SBA and variable increases in other liver enzymes
Hepatocellular atrophy and necrosis, fibrosis and biliary hyperplasia.
What diagnostic tests can be used for confirmation of Portosystemic shunt?
- CT with contrast
- Ultrasound with trans-splenic injection of agitated saline and concurrent cardiac ultrasound
- Trans-rectal scintigraphy
- Intra-operative contrast radiography or fluoroscopy
What are the clinical signs and reported predisposing conditions to portal vein thrombosis?
- Clinical signs include diarrhoea (likely due to increased mesenteric venous pressure) and hepatic encephalopathy due to acquired portosystemic shunting.
- Neoplasia may predispose to thrombosis
- Cirrhosis may result in thrombosis
- In foals, following enteritis or in association with R. equi infection.
- Secondary to hypercoagulability due to systemic disease/inflammation
True or false: extrahepatic biliary atresia is considered congenital.
True
Which lobe of the liver is most susceptible to torsion?
The left medial or accessory lobe is most commonly affected.
Entire left lobe torsion has also been reported.
List clinical signs and diagnostic findings described for liver lobe torsion
Anorexia, tachycardia, clinical and laboratory signs of systemic inflammation secondary to necrosis of the twisted lobe and peritonitis.
Peritoneal fluid is often sanguineous (peritonitis is always present), increases in SDH and GLDH may be present but overall liver enzyme elevation is often unremarkable.
The affected lobe may appear as a mixed echogenic mass on ultrasound if visible (often obscured by a gas-filled colon).
What is the treatment for liver lobe torsion
Surgical repair via stapled resection.
What are the other bacterias associated whit bacterial hepatitis?
- Salmonella
- E coli
- Citrobacter
- Klepbsiella
- Aeromonas
- Clostridium
- Actinobacter
what acute phase proteins are produce in liver?
- Fibrinogen
- SAA
- Plasminogen
- Complement
- Haptoglobin
- Ceruloplasmin
- Ferritin
- C Reactive protein.
