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

Six ponies and four horses with a mean (sd) age of 15.9 (6.0) years developed sudden-onset bilateral laryngeal paralysis (BLP) in association with hepatic dysfunction. Nine of them had been referred for the investigation of respiratory distress, and one pony had been referred for weight loss before BLP developed. Nine of the animals had clinicopathological evidence of liver disease, and nine had histological evidence of liver disease. All of the animals had one or more of the following: hepatic encephalopathy (in eight), hyperammonaemia (in six) and endoscopic evidence of BLP (in nine). Three of the animals had signs of pituitary pars intermedia dysfunction, a diagnosis supported in two by endocrine function testing, and in two by histopathological examination. Histopathological examination of the intrinsic laryngeal musculature and recurrent laryngeal nerves of four of the horses and of the region of the nucleus ambiguus of two did not reveal any abnormalities. Three of the animals were euthanased after they had first been examined, and one improved temporarily before the condition recurred. A temporary tracheostomy was performed in six of the animals, five of which subsequently died or were euthanased; one pony recovered.