The effect of bilateral glossopharyngeal nerve anaesthesia on swallowing in horses.

Summary Reasons for performing study: Dysfunction of the glossopharyngeal nerve has been implicated as a cause of dysphagia in horses. However, recent studies have indicated that this is not the case. Objectives: To determine whether bilateral glossopharyngeal nerve anaesthesia would cause dysphagia in horses or result in measurable alterations in the timing, function, or sequence of swallowing. Methods: Swallowing was evaluated in 6 normal horses with and without bilateral glossopharyngeal nerve anaesthesia. Swallowing dynamics were assessed subjectively and objectively based on time from prehension of food until swallowing, number of tongue movements until initiation of swallowing, depth of bolus at the base of the tongue prior to initiation of swallow and evidence of tracheal aspiration using fluoroscopy and endoscopy. Results: There was no evidence of aspiration or dysphagia in horses before or after bilateral glossopharyngeal nerve block. No observed or measured differences in swallowing sequence or function could be detected in blocked compared to unblocked horses. However, there was a trend in blocked horses for the number of tongue pushes and the time to swallowing to be increased. Conclusions: Glossopharyngeal nerve function may not be essential for normal swallowing function in otherwise healthy horses. Potential relevance: Clinically, normal swallowing is not an appropriate test of glossopharyngeal nerve function and dysphagic horses should not be assumed to have glossopharyngeal nerve dysfunction.