Bilateral laryngeal paralysis associated with hepatic dysfunction and hepatic encephalopathy in six ponies and four horses.

This study explores a case of sudden bilateral laryngeal paralysis (affecting both sides of the larynx) in six ponies and four horses linked to hepatic (liver-based) dysfunction. Outcomes varied among the 10 equines, with most showing evidence of liver disease and experiencing heightened ammonia levels or hepatic encephalopathy, a decline in brain function as a result of severe liver disease. Three animals showed signs of pituitary pars intermedia dysfunction, a condition that affects the endocrine system. Limited recoveries were made, with three animals euthanised shortly after examination, and others either dying or being euthanised after temporary tracheostomy.

Key Findings

• The research involved six ponies and four horses with an average age of around 16 years. These animals developed sudden bilateral laryngeal paralysis – a condition where both sides of the larynx or voice box stop working.
• Nine of these horses were referred for respiratory problems, while one pony was referred due to weight loss.
• Across the group, nine animals had evidence of liver disease, through both clinical pathology and histology (the study of organic tissues).
• Key symptoms across the animals included hepatic encephalopathy (a condition where the brain is affected due to liver function failure) in eight, hyperammonaemia (excess ammonia in the blood which can harm the central nervous system) in six, and endoscopic evidence of bilateral laryngeal paralysis in nine of them.
• Three of the horses had signs of pituitary pars intermedia dysfunction. This condition affects the endocrine system and disrupts hormone production. It was substantiated via endocrine function testing in two, and histopathological examination in two cases.
• Despite the various symptoms, histopathological examinations of the laryngeal musculature and laryngeal nerves, as well as the nucleus ambiguus region, showed no abnormalities in the examined animals.
• Initial treatment outcomes were poor, with three animals being euthanised shortly after examination, one showing temporary improvement, and six undergoing a temporary tracheostomy (creating an opening in the windpipe). Of these, five died or were euthanised, and one pony recovered.

Interpretation and Implications

• The study clearly establishes a link between sudden bilateral laryngeal paralysis and hepatic dysfunction in the sample group of ponies and horses.
• Hepatic encephalopathy, hyperammonaemia, and pituitary pars intermedia dysfunction were significant manifestations in these cases, suggesting these may interact or influence the occurrence of bilateral laryngeal paralysis.
• The relatively high rate of mortality following treatment suggests further research is needed to develop more effective therapies for this group of symptoms and associated conditions in horses.