PATHOLOGY - Equine Hepatobiliary Disease Flashcards
What are the general clinical signs of hepatopathies in horses?
Lethargy
Anorexia
Weight loss
Colic
Jaundice
Photosensitivity
Clinical signs of hepatic encephalopathy
They can be very non-specific
What is photosensitivity?
Photosensitivity is a heightened skin sensitivity to ultraviolet (UV) light
What causes primary photosensitivity?
Primary photosensitivity is due to primary intoxication of plant-derived photodynamic agents which interact with UV light to produce local free radicals and reactive oxygen species with cause skin damage
What causes secondary photosensitivity?
Secondary photosensitivity is due to accumulation of plant derived photodynamic agents - phylloerythrin which is a metabolite of chlorophyll - secondary to altered hepatic metabolism. These photodynamic agents interact with UV light to produce local free radicals and reactive oxygen species with cause skin damage
Where are photosensitivity lesions most commonly seen?
Photosensitivity lesions are most commonly seen on unpigmented skin frequently exposed to UV light
What should always be investigated if a horse presents with photosensitivity?
If a horse presents with photosensitivity you should always investigate liver parameters
How do you treat photosensitivity?
Treat underlying disease
Cover skin and treat locally (there is suncream available for horses)
What are the clinical signs of hepatic encephalopathy in horses?
Depression
Yawning
Anorexia
Head pressing
Circling
Ataxia
Blindness
Aggression
Somnolence
Comatose
How do you manage hepatic encephalopathy in horses?
Nutritional support
Antibiotics
Lactulose
Treat factors that can worsen the hepatic encephalopathy (usually with fluid therapy)
Why are antibiotics used in the management of hepatic encephalopathy?
Antibiotics are used in the management of hepatic encephalopathy to reduce ammonia producing enteric bacteria
Why is lactulose used in the management of hepatic encephalopathy?
The breakdown of lactulose to lactate in the colon leads to acidification of the colon contents, which will favour the conversion of ammonia (NH3) to ammonium (NH4) which cannot be absorbed across the cell membranes into the bloodstream. Furthermore, lactulose is a laxative which will decrease the time available for ammonie (NH3) to be absorbed into the bloodstream from the gastrointestinal tract
Which factors can exacerbate clinical signs of hepatic encephalopathy?
Dehydration
Hypokalaemia
Alkalaemia
Gastrointestinal haemorrhage
What are some of the less common clinical signs of hepatopathies in horses?
Diarrhoea
Coagulopathy
Ascites
Bilateral laryngeal paralysis
Pyrexia
Endotoxaemia
Polydipsia
Pigmenturia
Pruritis
Tenesmus
Steatorrhoea
How do you approach investigating hepatopathies in horses?
History and clinical signs
Clinical examination
Biochemistry and haematology
Liver function tests
Ultrasound
Liver biopsy
Which liver enzymes are markers of hepatocellular damage in horses?
Sorbitol dehydrogenase (SDH)
Glutamate dehydrogenase (GLDH)
Aspartate aminotransferase (AST)
Lactate dehydrogenase (LDH)
Where in the body is sorbitol dehydrogenase (SDH) found?
Sorbitol dehydrogenase (SDH) is found in the hepatic cytosol
What should you be aware of when assessing sorbitol dehydrogenase (SDH) levels?
Sorbitol dehydrogenase (SDH) has a very short half life and thus will not remain in the bloodstream for long periods of time
Where in the body is glutamate dehydrogenase (GLDH) found?
Glutamate dehydrogenase (GLDH) is found in the hepatic cytosol
Where in the body is aspartate aminotransferase (AST) found?
Aspartate aminotransferase (AST) is found in the hepatic cytosol, cardiac muscle and skeletal muscle
Less specific marker of hepatocellular damage
Which liver enzymes are markers of cholestasis in horses?
Gamma glutamate dehydrogenase (GGT)
Alkaline phosphatase (ALP)
Which liver function tests can be done on the horse?
Bile acid stimulation test
Serum bilirubin levels
Serum ammonia levels
What can ultrasound be used to evaluate when investigating equine hepatopathies?
Hepatic parenchyma
Vasculature (hepatic veins and portal veins)
Biliary ducts (hard to see)
How should the hepatic parenchyma usually appear on ultrasound?
The hepatic parenchyma should usually be homogenous with a medium echogenicity
On which side of the horse will you get the best view of the liver on ultrasound?
In horses, you will get the best view of the liver on the right side using ultrasound. Due to the liver’s cranial position, it can be obscured by the lung lobes, especially on the left side
What should you always do before taking a liver biopsy?
Coagulation tests
How do you carry out a liver biopsy in a horse?
You can either do an ultrasound guided liver biopsy from the right side of the horse or you can perform the biopsy between the 12th to 14th intercostal spaces and midway between two lines drawn between the shoulder and the tuber coxae, and the point of the elbow and the tuber coxae
What is the main potential complication of a liver biopsy?
Haemorrhage
What are the most common infectious liver diseases seen in horses?
Tyzzer’s disease
Cholangiohepatitis
Theiler’s disease
Which pathogen causes Tyzzer’s disease in horses?
Clostridium piliforme
Which signalement typically presents with Tyzzer’s disease?
Foals
What are the clinical signs of Tyzzer’s disease?
Sudden death
Clinical signs of acute hepatitis
Clinical signs of acute enteritis
How do you diagnose Tyzzer’s disease?
Liver biopsy and histopathology using silver staining (Warthin-Starry stain)
Faecal PCR
What is the prognosis for Tyzzer’s disease?
Often Tyzzer’s disease is fatal
What is cholangiohepatitis?
Cholangiohepatitis is acute inflammation of the biliary ducts and the liver parenchyma
What is the main cause of cholangiohepatitis in horses?
Cholangiohepatitis occurs secondary to diseases which allow for ascending bacterial infections
How do you diagnose cholangiohepatitis in horses?
Liver biopsy, histopathology and culture and sensitivity
How do you treat cholangiohepatitis?
You can treat cholangiohepatitis with a 4 to 6 weeks course of antibiotics based on culture and sensitivity
Which pathogen causes Theiler’s disease?
Several viruses have been isolated in patients with Theilier’s disease
What is a risk factor for Theiler’s disease?
Theiler’s disease can develop as a complication of blood/plasma transfusions in horses
What is the most significant hepatotoxicity seen in horses?
Pyrrolizidine alkaloid toxicity
List examples of plants containing pyrrolizidine alkaloids
Ragwort
Senecia
How do pyrrolizidine alkaloids cause chronic hepatotoxicity?
Pyrrolizidine alklaloids are typically not palatable to horses and thus they do not ingest them, however if there is insufficient forage or the pyrrolizidine alkaloids are incorporated into hay, pellets etc, this can cause chronic, low-level exposure of pyrrolizidine alkaloids which are metabolised by the liver into toxic pyrroles which can interact with DNA. Toxic pyrroles have an antimitotic effect resulting in megalocytosis and inhibit protein synthesis resulting in fibrosis - causing a chronic megalocytic hepatopathy
What is megacytosis?
Megacytosis is where hepatocytes exhibit enlargement of cytoplasmic and nuclear volume without formation of mitotic spindles and mitosis, indicative of irreversible cellular damage
When do clinical signs of pyrrizidine alkaloid toxicity typically arise?
Clinical signs of pyrrizidine alkaloid toxicity typically arise 4 weeks to 12 months following consumption
What are the clinical signs of pyrrizidine alkaloid toxicity?
Anorexia
Weight loss
Lethargy
Mild jaundice
Hepatic encephalopathy
How do you diagnose pyrrizidine alkaloid toxicity?
Liver biopsy and histopathology
What are the key features of pyrrizidine alkaloid toxicity on histopathology?
Bridging fibrosis
Bile duct hyperplasia
Megalocytosis
How do you manage pyrrizidine alkaloid toxicity?
Dietary management
Anti-fibrotic drugs (not usually effective)
How can you monitor the progression of pyrrizidine alkaloid toxicity?
Serial monitoring of liver enzymes to monitor the progression of disease
What is the prognosis for pyrrizidine alkaloid toxicity?
Usually a grave prognosis
What is the proposed cause of chronic hepatitis is horses?
|Chronic hepatitis is rare in horses
Autoimmune disease
How do you diagnose chronic hepatitis?
Liver biopsy and histopathology
How do you treat chronic hepatitis?
Immunosuppressive therapy (with dexamethosone)
What is cholelithiasis?
Cholelithiasis is the calcification of the components of bile - bilirubin, bile acids and cholesterol - to form biliary stones
What are choleliths?
Choleliths is the general term used to describe bile stones located anywhere within the biliary tract
What are hepatoliths?
Hepatoliths is the term used to describe bile stones located in the intrahepatic biliary ducts
What are choledocholiths?
Choledocholiths is a term used to describe bile stones located in the common bile duct
Which signalement typically presents with cholelithaisis?
Middle aged horses (6 to 15 years old)
What is the proposed cause of cholelithiasis?
The proposed cause of cholelithiasis is an ascending bacterial infection from the duodenum
What is one of the main potential consequences of cholelithiasis?
The pressure from the cholelith and the biliary stasis can cause biliary necrosis and fibrosis
How do you treat cholelithiasis?
Broad spectrum antibiotics
Surgical removal of the cholelith
Which hepatic neoplasms can be seen in young horses?
|Hepatic neoplasia is rare in horses
Hepatocellular carciomas
Which hepatic neoplasms can be seen in older horses?
|Hepatic neoplasia is rare in horses
Cholangiocarcinomas
