Partial paralysis of the larynx prevents maximal opening of the equine trachea. Affected horses can move air, but breathing noises occur, especially during exercise. The most common form of laryngeal paralysis is recurrent laryngeal neuropathy (RLN), which involves degeneration of the recurrent laryngeal nerve. The cause of RLN is unknown, but it seems to affect large, young Thoroughbred horses in particular. A recent study from the University of Edinburgh in Scotland followed a large, mixed-breed population of working horses with laryngeal paralysis to better characterize the features of this disease.
Over 13 years, 375 horses were evaluated. RLN was diagnosed in 351 (94%), versus 24 with laryngeal paralysis secondary to known nerve injury. Eighty-five percent of the RLN horses were Thoroughbreds or Thoroughbred crosses, as expected.
Using endoscopy, laryngeal movements were examined and graded from 0 (no problem with movement) to 5 (total lack of movement of one or both sides of the larynx). Ninety-six percent of RLN cases were unilateral and left-sided, which is typical. The average grade for RLN horse was 4, corresponding with a marked lack of opening of the larynx, even during exercise. There was no age or gender predilection for RLN, although most horses (42%) were National Hunt racing horses. Only 1% were horses raced on the flat.
Ninety percent of RLN horses made respiratory noises during exercise, and 64% had decreased exercise tolerance. Of the 24 animals with non-RLN paralysis, 11 were cases of bilateral involvement in ponies with liver disease or recent general anesthesia. In contrast, seven of the remaining 12 cases with unilateral involvement were due to guttural pouch infections.
Dixon, P.M.; McGorum, B.C.; Railton, D.I.; et al. Equine Veterinary Journal, 33(5), 452-458, 2001.
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