Diagnostic Sensitivity of Subjective and Quantitative Laryngeal Ultrasonography for Recurrent Laryngeal Neuropathy in Horses

Abstract

Recurrent laryngeal neuropathy (RLN) is the most common cause of laryngeal hemiplegia in horses and causes neurogenic atrophy of the intrinsic laryngeal muscles, including the cricoarytenoideus lateralis muscle. Recurrent laryngeal neuropathy results in paresis to paralysis of the vocal fold and arytenoid cartilage, which limits performance through respiratory compromise. Ultrasound has previously been reported to be a useful diagnostic technique in horses with RLN. In this report, the diagnostic sensitivity of subjective and quantitative laryngeal ultrasonography was evaluated in 154 horses presented for poor performance due to suspected upper airway disease. Ultrasonographic parameters recorded were: cricoarytenoideus lateralis echogenicity (subjective and quantitative), cricoarytenoideus lateralis thickness, vocal fold movement, and arytenoid cartilage movement. Ultrasonographic parameters were then compared with laryngeal grades based on resting and exercising upper airway endoscopy. Subjectively increased left cricoarytenoideus lateralis echogenicity yielded a sensitivity of 94.59% and specificity of 94.54% for detecting RLN, based on the reference standard of exercising laryngeal endoscopy. Quantitative left cricoarytenoideus lateralis echogenicity values differed among resting laryngeal grades I-IV. Findings from this study support previously published findings and the utility of subjective and quantitative laryngeal ultrasound as diagnostic tools for horses with poor performance.

Development of a quantitative method for ultrasonographic assessment of recurrent laryngeal neuropathy in horses

“…Recent studies highlighted that abnormal arytenoid movement during dynamic endoscopic exam was statistically associated with relative hyperechogenicity of the cricoarytenoideus lateralis muscle Chalmers et al 2012). Subjective hyperechogenicity of the left cricoarytenoideus lateralis muscle had a sensibility of 94.59% and a specificity of 94.54% for the detection of RLN (Chalmers et al 2012). These findings are consistent with reports in human medicine, in which quantitative measures of muscle echogenicity have been proposed as methods for enhancing detection of neuromuscular pathologies.…”

“…Yet, no significant difference was observed in left cricoarytenoideus lateralis raw echogenicity between the grade A and grade B horses (Chalmers et al 2012).…”

“…The relevance of quantitative assessment of the cricoarytenoideus lateralis echogenicity for RLN diagnosis has previously been described (Chalmers et al 2012). A recent report evaluated the relationship between ultrasonographic appearance of the cricoarytenoideus lateralis muscle and its histological composition after right recurrent laryngeal transection.…”

“…Increased cricoarytenoideus lateralis muscle echogenicity was associated with histological markers of muscle atrophy including reduced mean fiber diameter, increased collagen content, increased fiber density, and as a later stage change, increased fat content (Maurtis et al 2003;Chalmers-Chaudhry, 2014). In naturally occurring RLN, progressive alterations in fiber diameter and infiltration with fibrous connective tissue and fat increase the number of reflections within the muscle and therefore the mean gray value of the muscle in the ultrasound image (Cahill & Goulden, 1986;Pillen, 2010;Chalmers et al 2012). Quantitative gray-scale analysis has been shown to improve the reliability and sensitivity of muscle ultrasound for the detection of neuromuscular disorders in children compared to visual evaluation alone (Pillen, 2006).…”

“…Beyond these muscles, the cricoarytenoideus lateralis muscle is the first one to undergo neurogenic atrophy and is histologically the most severely affected in RLN (Cahill & Goulden, 1986;Duncan et al 1974). Recent studies highlighted that abnormal arytenoid movement during dynamic endoscopic exam was statistically associated with relative hyperechogenicity of the cricoarytenoideus lateralis muscle Chalmers et al 2012). Subjective hyperechogenicity of the left cricoarytenoideus lateralis muscle had a sensibility of 94.59% and a specificity of 94.54% for the detection of RLN (Chalmers et al 2012).…”