Muscular pathology in equine laryngeal neuropathy

Three adductor muscles of the larynx, the cricoarytenoideus lateralis (CAL), the arytenoideus transversus (AT) and the ventricularis (Ve), from 36 horses were examined histologically. The neurogenic changes seen in each muscle were evaluated qualitatively. In addition, in 6 horses with clinical and subclinical signs of neurogenic atrophy, measurements of muscle fibre area were performed. Neurogenic changes observed in the Ve were less than in CAL and AT. Measurements of muscle fibre area also demonstrated that CAL and AT showed a wider range of pathological changes than did Ve. The results show that denervation does not uniformly affect all adductor muscles of the larynx. On the other hand, the appearance in some animals of fibre type grouping in the right AT to the same or to a greater extent than in the left AT supports the classification of equine laryngeal neuropathy as a distal axonopathy.