Post anaesthetic myelopathy in the horse: a case report

The first case of post anaesthetic myelopathy in a horse is described. A two year old 530 kg Shire stallion underwent surgical removal of a granuloma in the ventral sternal region under general inhalation anaesthesia in dorsal recumbency. Total duration of the operation was 85 min. The anaesthesia was uneventful except for profuse sweating and arterial hypertension observed during the whole period. During recovery the horse was not able to stand, and flaccid paralysis of hind limbs, absence of reaction to an induced pain stimulus on the hind limbs and no patellar or anal reflex was recorded; in addition, tail tonus was weak. Panniculus reflex was absent distally from the 17th intercostal space. Head, neck and front limb movement was not affected. The horse did not respond to treatment by intravenous administration of dexamethasone, hypertonic or isotonic saline. The status deteriorated and the horse was euthanised 4 h after the end of anaesthesia. The main pathological findings were haemorrhage, oedema and malacia of L5-L6 spinal cord segments and cauda equina. Histological examination of the spinal cord revealed haemorrhage and areas of necrosis predominantly in the grey matter of L5 and L6 segments. Impairment of spinal cord perfusion due to haemodynamic changes associated with dorsal recumbency and general anaesthesia is presumed. Predisposition factors could include young age, dorsal recumbency and high weight.