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Ultrasonographic detection of early atrophy of the intrinsic laryngeal muscles of horses

Heather J. Chalmers DVM, PhD1, Laurent Viel DVM, PhD2, Jeff L. Caswell DVM, PhD3, and Norm Ducharme DVM, MS4
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  • 1 Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
  • | 2 Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
  • | 3 Department of Pathobiology, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.
  • | 4 Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853.

Abstract

OBJECTIVE To describe the ultrasonographic changes in the cricoarytenoideus dorsalis (CAD) and cricoarytenoideus lateralis (CAL) muscles of horses before and at various times during the 32 weeks after unilateral neurectomy of the right recurrent laryngeal nerve.

ANIMALS 28 healthy Standardbreds.

PROCEDURES For each horse, the appearance of the CAD and CAL muscles on the right (neurectomized) and left (control) sides was serially monitored ultrasonographically by percutaneous (CAD and CAL) and transesophageal (CAD) approaches. The ultrasonographic images were assessed to determine the mean pixel intensity, muscle thickness, and appearance grade, and comparisons were made between the muscles of the neurectomized and control sides.

RESULTS The muscle appearance grade and mean pixel intensity for the CAL and CAD muscles on the neurectomized side were significantly increased by 2 and 4 weeks, respectively, after the neurectomy. The transesophageal approach enhanced the ultrasonographic visibility of the CAD muscle and allowed us to detect a significant decrease in the thickness of the CAD muscle on the neurectomized side over time, compared with thickness of the CAD muscle on the control side.

CONCLUSIONS AND CLINICAL RELEVANCE Results suggested ultrasonography can be used to successfully assess the CAL and CAD muscles of horses. A qualitative grading scheme was sufficient for successful detection and monitoring of muscle atrophy and reduced the need for image standardization. The transesophageal approach described for assessment of the CAD muscle warrants further investigation.

Contributor Notes

Address correspondence to Dr. Chalmers (heather.chalmers@uoguelph.ca).