Horner's syndrome in the horse: experimental induction and a case report

The findings in 6 experimental and 1 natural case of Horner's Syndrome (HS) are presented. The experimental cases were induced by unilateral surgical section of the cervical sympathetic trunk in the middle third of the neck. The naturally occurring case was seen in a 17 year old gelding with a mediastinal tumour. The signs of HS in these horses included ptosis, miosis, enophthalmos, hemilateral sweating and temperature increase of the face and cranial cervical region on the affected side. The intensity of these signs was variable between and within animals. Miosis, enophthalmos and temperature difference were sometimes difficult to discern. Clinically the recognition of HS is important in the localization of lesions, and when accompanied by nasal haemorrhage is highly suggestive of guttural pouch mycosis.