Recurrent laryngeal neuropathy (RLN) is a distal axonopathy of the recurrent laryngeal nerve. Current diagnostics rely upon disease recognition in the clinically affected horse, with no ante-mortem test yet available to detect subclinical muscle fiber changes. The purpose of the present study was to validate a novel method of muscle retrieval from the equine larynx in the standing horse. First, an immunohistochemical comparison of muscle fiber types was made between the left cricoarytenoideus lateralis and the cricoarytenoideus dorsalis in six endoscopically normal horses. Similar muscle isoforms were found in both, but the lateralis was found to have a greater percentage of type 2a and fewer type 1 fibers than the dorsalis. Also, in horses with subclinical RLN (as evident by fiber type regrouping), there were significant regional variations of muscle types within the lateralis, not found in the dorsalis. Subsequently, ultrasound guided biopsy of the left cricoarytenoideus lateralis was performed in six, sedated horses, which were then monitored for complications. The procedure was well tolerated and biopsy specimens suitable for immunohistochemical analysis were successfully obtained in all horses. No major complications were noted following the procedure. Ultrasound guided biopsy provided a minimally invasive and effective method to obtain cricoarytenoideus lateralis muscle samples in horses.
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