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HE may be precipitated by severel conditions in animals, all of which cause an increase in the blood concentrations of ammonia and/or mercaptans:
 
HE may be precipitated by severel conditions in animals, all of which cause an increase in the blood concentrations of ammonia and/or mercaptans:
*'''Metabolic alkalosis'''
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*'''Metabolic alkalosis''' increases the production of ammonia by the kidneys and increases the uptake of urea across the blood brain barrier.
 
*'''Hypokalaemia'''
 
*'''Hypokalaemia'''
 
*'''Constipation''', increasing the length of time that colonic bacteria are able to act on undigested amino acids.
 
*'''Constipation''', increasing the length of time that colonic bacteria are able to act on undigested amino acids.
 
*'''Gastro-intestinal haemorrhage''', increasing the amount of protein available to GI bacteria.
 
*'''Gastro-intestinal haemorrhage''', increasing the amount of protein available to GI bacteria.
 
*'''Diet with a high protein, purine or methionine content'''
 
*'''Diet with a high protein, purine or methionine content'''
*'''Azotaemia'''
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*'''Azotaemia''', increasing the concentration of urea in the GI tract and also causing GI haemorrhage if [[Uraemia|uraemia]] develops.
*'''Hypermetabolic state or fever''', as may occur in many forms of systemic illness due to the effects of inflammatory cytokines and which leads to the catabolism of lean body protein.
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*'''Hypermetabolic state or fever''', as may occur in many forms of systemic illness due to the effects of inflammatory cytokines and which leads to the catabolism of lean body protein.  A similar phenemenon may occur if glucocorticoids are administered at high doses.
 
*'''Dehydration''' increases the effective circulating ammonia concentraton.
 
*'''Dehydration''' increases the effective circulating ammonia concentraton.
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===Diagnostic Imaging===
 
===Diagnostic Imaging===
 
Imaging is not required to make a diagnosis of HE but it may reveal abnormalities relating to the underlying cause.
 
Imaging is not required to make a diagnosis of HE but it may reveal abnormalities relating to the underlying cause.
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==Pathology==
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Myelin degeneration, consisting of vacuoles between the grey and white matter, may be observed on histopathological examination of cerebral tissues from affected animals.
    
==Treatment==
 
==Treatment==
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==From Pathology==
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===Clinical===
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*non-specific neurological signs (attributed to the retention of ammonia and gamma aminobutyric acid in [[Liver - Anatomy & Physiology|liver]] failure and their effects on the brain)
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**dullness
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**apparent unawareness of surroundings
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**pointless or compulsive movements
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**mania
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**generalised convulsions
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NB: usually soon followed by death
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===Microscopically===
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*lesions in the brain vary in expression
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**most species may show myelin degeneration consisting of vacuoles between the grey and white matter
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**the horse may show very little visible neural changes, perhaps an increase in astrocytes
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===Causes===
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::[[Portosystemic Shunt|Portosystemic Shunting]]
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::Chronic [[Liver - Anatomy & Physiology|liver]] damage
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*due to ingestion of toxic compounds over a long period of time
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*E.g. [[Ragwort|ragwort]] [[Category:Liver_-_General_Pathology]]
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[[Category:Liver_-_General_Pathology]]
 
[[Category:Dog]][[Category:Cat]]
 
[[Category:Dog]][[Category:Cat]]
   
[[Category:To_Do_-_James]]
 
[[Category:To_Do_-_James]]
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