External transcutaneous ultrasound technique in the equine cricoarytenoideus dorsalis muscle: Assessment of muscle size and echogenicity with resting endoscopy.
Authors: Satoh Masato, Higuchi Tohru, Inoue Satoshi, Miyakoshi Daisuke, Kajihara Ayako, Gotoh Tadahiro, Shimizu Yasuhito
Journal: Equine veterinary journal
Summary
# Editorial Summary Recurrent laryngeal neuropathy (RLN) remains a significant performance-limiting condition in horses, yet current diagnostic approaches rely heavily on endoscopic assessment. Satoh and colleagues evaluated whether external transcutaneous ultrasonography could reliably measure the cricoarytenoideus dorsalis muscle (CAD) as an alternative diagnostic tool, comparing muscle thickness, cross-sectional area and echogenicity between 164 horses stratified by resting laryngeal grade using the Havemeyer classification. Horses with advanced RLN (grades 3 and above) demonstrated significantly reduced left CAD to right CAD ratios for both thickness (0.69) and area (0.66), alongside increased hyperechogenicity of the affected muscle, with thickness and area showing negative correlation to disease severity. The transcutaneous technique proved comparable to previously published transoesophageal ultrasonography findings whilst offering practical advantages—being non-invasive, requiring no special equipment beyond standard ultrasound machines, and eliminating the need for oesophageal intubation. For equine practitioners, this approach offers a straightforward bedside assessment method to objectively quantify laryngeal muscle atrophy and guide clinical decision-making regarding surgical intervention, particularly when distinguishing between laryngoplasty candidates and those who might benefit from nerve grafting procedures.
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Practical Takeaways
- •External transcutaneous ultrasound is a practical, noninvasive alternative to transoesophageal ultrasound for diagnosing recurrent laryngeal neuropathy in horses—no need for expensive endoscope equipment or invasive techniques
- •Measuring left-to-right muscle thickness and cross-sectional area ratios provides objective criteria to help decide whether a horse needs laryngoplasty or nerve graft procedures
- •Asymmetric atrophy and hyperechogenicity of the left cricoarytenoideus dorsalis muscle on ultrasound can be used as a screening tool to identify RLN suspects before or alongside endoscopic examination
Key Findings
- •LCAD:RCAD thickness and area ratios were 0.69 and 0.66 respectively in horses with resting grades 3 and 4, indicating significant atrophy of the left cricoarytenoideus dorsalis muscle in affected horses
- •LCAD:RCAD ratios in grades 3.II, 3.III and 4 were significantly lower than control horses, with negative correlation between LCAD thickness/area and resting laryngeal grade
- •Left cricoarytenoideus dorsalis muscle showed increased hyperechogenicity in horses with resting grades 3 and 4 compared to the right muscle
- •Transcutaneous ultrasonography results were comparable to transoesophageal ultrasonography, offering a simpler, noninvasive diagnostic alternative for assessing RLN