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==From Pathology==
−===Clinical===
−*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)
−**dullness
−**apparent unawareness of surroundings
−**pointless or compulsive movements
−**mania
−**generalised convulsions
−NB: usually soon followed by death
−===Microscopically===
−*lesions in the brain vary in expression
−**most species may show myelin degeneration consisting of vacuoles between the grey and white matter
−**the horse may show very little visible neural changes, perhaps an increase in astrocytes
−===Causes===
−::[[Portosystemic Shunt|Portosystemic Shunting]]
−::Chronic [[Liver - Anatomy & Physiology|liver]] damage
−*due to ingestion of toxic compounds over a long period of time
−*E.g. [[Ragwort|ragwort]] [[Category:Liver_-_General_Pathology]]
+
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'''
+*'''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'''
+*'''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.
+*'''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.
+
+==Pathology==
+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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−[[Category:Liver_-_General_Pathology]]
[[Category:Dog]][[Category:Cat]]
[[Category:Dog]][[Category:Cat]]
−[[Category:To_Do_-_James]]
[[Category:To_Do_-_James]]