Dorsal displacement of the soft palate (DDSP) occurs when the caudal free-margin of the soft palate displaces dorsal to the epiglottis. The result is partial expiratory obstruction and noise during intense exercise, as well as reduced performance. The condition is almost always intermittent and may occur only during exercise. Diagnosis is performed via endoscopic (static endoscopy if displacement is persistent, dynamic if displacement is intermittent) examination. Treatment is based on clinical and endoscopic evaluation. The most performed surgical procedure for treatment of DDSP is the laryngeal tie-forward, aimed at bringing the larynx into a more rostral and dorsal location.
Etiology and Pathogenesis of Dorsal Displacement of the Soft Palate in Horses
The pathophysiologic mechanisms that result in dorsal displacement of the soft palate are poorly understood. Current research points to neuromuscular dysfunction of the pharyngeal muscles important in maintaining palatal stability. Contributing etiologic factors may include hypoplasia or flaccidity of the epiglottis, and/or positional derangements of both the larynx and hyoid apparatus. Hypoplasia or flaccidity of the epiglottis results in an inability to maintain the caudal border of the soft palate in its normal, ventral location during intense exercise. In addition, the presence of masses, granulomas, or cysts located below the epiglottis and along the caudal free border of the soft palate can lead to palate displacement. Horses with a more caudal larynx or more ventral hyoid apparatus (assessed by position of the basihyoid bone) may be more prone to dorsal displacement of the soft palate. Lastly, horses that have undergone laryngoplasty for left laryngeal hemiplegia are more likely to develop DDSP.(1 References Dorsal displacement of the soft palate captured on static endoscopy. Note that the caudal free edge of the soft palate obscures the epiglottis. The corniculate processes of the arytenoid cartilage... read more )
Diagnosis of Dorsal Displacement of the Soft Palate in Horses
Laryngeal imaging (radiography and ultrasonography)
Horses present with a history of poor performance in association with an expiratory noise. DDSP creates a characteristic gurgling respiratory noise, primarily during expiration, due to vibration of the soft palate. Horses may make no noise at the onset of exercise but displace their palate during high-speed exercise, causing them to “choke down.”
Dynamic endoscopy should be performed on all cases in which DDSP is suspected. During dynamic endoscopy, DDSP will occur toward the end of intense, high speed exercise. Before DDSP occurs, the soft palate will billow and the horse increases swallowing. This swallowing is thought to be an attempt at stabilizing the palate. The intensity of exercise and the horse’s head position can affect the occurrence of DDSP, making the type of dynamic endoscopy (treadmill or overground) an important consideration in diagnosis. If dynamic endoscopy is not possible, static endoscopy should be performed immediately after exercise.
Radiographic or ultrasonographic evaluation of the laryngeal region may be used clinically to augment endoscopy, particularly when findings are inconclusive or when dynamic endoscopy is not available. These modalities can also be useful for post-operative evaluation in horses undergoing laryngeal tie-forward procedures. Radiographs of the larynx are obtained to evaluate the position of the larynx and determine if the location is too ventral and caudal, making DDSP more likely; laryngeal ultrasound is used to measure the depth of the basihyoid bone at the base of the lingual process, with increased depth significantly associated with DDSP.(2 References Dorsal displacement of the soft palate captured on static endoscopy. Note that the caudal free edge of the soft palate obscures the epiglottis. The corniculate processes of the arytenoid cartilage... read more )
Treatment of Dorsal Displacement of the Soft Palate in Horses
Surgical treatment (pursued only in horses > 3 years of age)
Inflammation of the upper respiratory tract can lead to neuropathy of the pharyngeal branch of the vagus nerve, which is important for pharyngeal muscular function. If inflammation of the respiratory tract is diagnosed along with DDSP, then rest and treatment of the underlying inflammatory condition is recommended. Other conservative management strategies focus on manipulation of the position of the laryngohyoid apparatus and include the use of different bits or a tongue tie to prevent caudal retraction of the tongue or a laryngohyoid support device meant to elevate the larynx ("Cornell collar").
Staphylectomy is performed only for horses that have a mass along the caudal free margin of the soft palate. Only a thin margin of soft palate should be resected, or dysphagia will result.
Palatoplasty is performed to stiffen the soft palate to prevent DDSP. A surgical laser is used to create small, multifocal burns along the caudal soft palate to create fibrosis of the soft palate. Injection of the soft palate with a stiffening agent (sclerotherapy) has also been used. Reported success rates are ~25%–50%.(3 References Dorsal displacement of the soft palate captured on static endoscopy. Note that the caudal free edge of the soft palate obscures the epiglottis. The corniculate processes of the arytenoid cartilage... read more )
Myectomy of the sternohyoideus, sternothyroideus +/- omohyoideus can be performed to decrease caudal traction on the larynx by the strap muscles.
Partial sternothyroideus myectomy and tenectomy is performed by transecting the insertional tendon of the sternothyroideus muscle along with removal of a small portion of the rostral muscle belly.
Laryngeal tie-forward is now the most commonly performed procedure for horses with DDSP. This procedure "ties" the back edge of the thyroid cartilage rostrally to the basi-hyoid bone, moving the larynx into a more dorsal and rostral location, mimicking the function of the thyrohyoideus muscle. Reported success rates after laryngeal tie-forward are ~80%.(4 References Dorsal displacement of the soft palate captured on static endoscopy. Note that the caudal free edge of the soft palate obscures the epiglottis. The corniculate processes of the arytenoid cartilage... read more )
Dorsal displacement of the soft palate occurs when the soft palate displaces dorsally, above the epiglottis.
DDSP causes reduced performance due to partial obstruction during expiration.
DDSP causes an expiratory respiratory noise.
Dynamic endoscopy is recommended for definitive diagnosis.
Laryngeal tie-forward is the most commonly used procedure to correct DDSP.
Barnett TP, O'Leary JM, Dixon PM, Barakzai SZ. Characterization of palatal dysfunction after laryngoplasty. Equine Vet J. 2014;46(1):60–63.
Chalmers HJ, Yeager AE, Ducharme N. Ultrasonographic assessment of laryngohyoid position as a predictor of dorsal displacement of the soft palate in horses. Vet Radiol Ultrasound. 2009 Jan-Feb;50(1):91–96.
Barakzai SZ, Boden LA, Hillyer MH, Marlin DJ, Dixon PM. Efficacy of thermal cautery for intermittent dorsal displacement of the soft palate as compared to conservatively treated horses: Results from 78 treadmill diagnosed horses. Equine Vet J. 2009;41(1):65–69.
Woodie JB, Ducharme NG, Kanter P, Hackett RP, Erb HN. Surgical advancement of the larynx (laryngeal tie-forward) as a treatment for dorsal displacement of the soft palate in horses: a prospective study 2001–2004. Equine Vet J. 2005;37:418–423.
For More Information
Barakzai S & Hawkes C. Dorsal Displacement of the soft palate and palatal instability. Equine Veterinary Education (2010) 22 (5) 253–264.
Also see pet health content regarding dorsal displacement of the soft palate in horses Dorsal Displacement of the Soft Palate in Horses Dorsal displacement of the soft palate is a condition of the upper respiratory tract that can limit performance in horses. It is a relatively common cause of upper respiratory noise during maximal... read more .