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?
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?
Alkaline phosphatase (ALP)
Gamma glutamate dehydrogenase (GGT)
Which liver function tests can be done on the horse?
Bile acid stimulation test
Serum bilirubin levels
Serum ammonia levels
When do serum bile acid levels increase?
Serum bile acid levels increase when there is cholestasis
When do serum bile acid levels decrease?
Serum bile acid levels decrease when there is decreased functional hepatic mass
When do serum bilirubin levels increase?
Serum bilirubin levels increase when there is cholestasis and when there is decreased functional hepatic mass
When do serum ammonia levels increase?
Serum ammonia levels increase when there is decreased functional hepatic mass, due to portosystemic shunts or due to gastrointestinal disease
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
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
How do you diagnose Tyzzer’s disease?
Liver biopsy and histopathology using silver staining (Warthin-Starry stain)
Faecal PCR
List two examples of plants containing pyrrolizidine alkaloids
Ragwort
Senecia
What are the key features of pyrrizidine alkaloid toxicity?
Bridging fibrosis
Bile duct hyperplasia
Megalocytosis
