Histological and ultrastructural evidence that recurrent laryngeal neuropathy is a bilateral mononeuropathy limited to recurrent laryngeal nerves

Reasons for performing study: Recurrent laryngeal neuropathy (RLN) is a common and debilitating peripheral nerve disease of horses, but it remains unclear if this disease is a mono- or polyneuropathy. An understanding of the distribution of the neuropathological lesions in RLN affected horses is fundamental to studying the aetiology of this very significant disease of tall horses. Objective: To determine whether RLN should he classified as a mono- or polyneuropathy. Methods: Multiple long peripheral nerves and their innervated muscles were examined systematically in 3 clinically affected RLN horses Results: Severe lesions were evident in the left as well as right recurrent laryngeal nerves in all horses, both distally and, in one case, also proximally. No primary axonal lesions were evident in other nerves nor were changes found in their innervated muscles. Conclusions: RLN is not a polyneuropathy but should be classified as a bilateral mononeuropathy. Potential relevance: Genetic and local factors specifically affecting the recurrent laryngeal nerves in RLN-affected horses should now be investigated further.