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Soft palate: dorsal displacement
Synonym(s): Choking down, DDSP
Introduction
- Abnormal position of soft palate and larynx.
- Performance limiting condition in the equine athlete.
- Cause: idiopathic or secondary to many possible underlying causes.
- Signs: can cause respiratory noise together with a dramatic drop in exercise tolerance; variable drop in performance associated with acute dyspnea; characteristic gurgling noise; and less often, severe respiratory obstruction.
- Diagnosis: history, signs, endoscopy at rest, on high-speed treadmill, and with dynamic (over ground) endoscopy.
- Treatment: conservative or surgical treatments. Success rates approximately 60-70% depending on surgical procedure performed.
- Prognosis: fair for complete resolution.
Presenting signs
- Respiratory noise.
- Poor performance.
- Exercise intolerance.
Age predisposition
- All ages (>2 years) that undergo fast competitive work.
Breed/Species predisposition
- Thoroughbreds Thoroughbred.
- Standardbreds Standardbred.
Cost considerations
- Underlying cause.
- Athletic expectations.
Pathogenesis
Etiology
- Idiopathic: neuromuscular dysfunction or incoordination between muscles of soft palate and possibly hyoepiglotticus muscle possibly due to fatigue, unfitness, local inflammation.
- Secondary to predisposing factors, eg guttural pouch inflammation or palatal cysts.
- Can be permanent or intermittent (more common form).
Excessively long soft palate is no longer considered to be a contributing cause.
Predisposing factors
General
- Fatigue:
- Unfitness.
- Cardiovascular disease Heart: disease - overview.
- Pulmonary disease.
- Airway obstruction Trachea: foreign body Pharynx: foreign body.
- Palate defects:
- Congenital/iatrogenic
. - Ulceration.
- Cysts.
- Congenital/iatrogenic
- Epiglottic defects.
- Hypoplasia.
- Entrapment Larynx: epiglottic entrapment.
- Forced breathing through mouth:
- Unsuitable bit.
- Excessive flexion of neck (dressage).
- Other upper respiratory tract conditions:
- Laryngeal hemiparesis Larynx: hemiplegia.
- Pharyngitis.
- Subepiglottic cysts.
- Neoplasia Respiratory: neoplasia.
- Presence of mucus (recurrent airway obstruction (RAO) Lung: recurrent airway obstruction (RAO)) or blood in nasopharynx (exercise-induced pulmonary hemorrhage Lung: EIPH (exercise-induced pulmonary hemorrhage)).
Pathophysiology
- Hypothetical dysfunction of the neuromuscular group: pharyngeal nerve(s), palatinus and palatopharyngeus muscles.
- Condition has been reproduced by local anesthesia of the pharyngeal branch of the vagus nerve (which innervates the palatinus muscle).
- Associated with lymph node inflammation in the floor of the medial compartment of the guttural pouch (associated with the pharyngeal branch of the vagus nerve).
- Transection of the omohyoid, sternohyoid, hyoepiglottic and thyrohyoid muscles → intermittent DDSP. These muscles influence the position of the hyoid apparatus and larynx.
- Severe exertion → billowing at junction of hard and soft palate → wave moves caudally along soft palate towards free edge.
- Concurrent caudal retraction of larynx and irregular breathing → soft palate slips out from under epiglottis and obstructs the rima glottidis.
- Swallowing may be associated with DDSP but usually occurs afterwards in an attempt to regain correct position of soft palate.
Diagnosis
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Treatment
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Prevention
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Outcomes
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Further Reading
Publications
Refereed papers
- Recent references from PubMed and VetMedResource.
- Lo Feudo C M, Stucchi L, Cavicchioli P et al (2022) Association between dynamic upper airway obstructions and fitness parameters in Standardbred racehorses during high-speed treadmill exercise. J Am Vet Med Assoc 270 (11), 1343-1350 PubMed.
- Vermedal H, O’Leary J M, Fjordbakk C T et al (2021) Outcome analysis of 95 harness racehorses with confirmed dorsal displacement of the soft palate treated with laryngeal tie-forward surgery. Equine Vet J PubMed.
- Davison J A, Lumsden J M, Boston R C & Ahern B J (2017) Overground endoscopy in 311 Thoroughbred racehorses: findings and correlation to resting laryngeal function. Aust Vet J 95 (9), 338-342 PubMed.
- Carmalt J L, Johanssen B & Waldner C (2016) Comparisons between staphylectomy and tie-forward procedures in combination with sternothryroideus myotenectomy for the treatment of intermittent dorsal displacement of the soft palate: An observational study. Vet Surg 45 (6), 816-823 PubMed.
- Allen K J, Christley R M, Birchall M A & Franklin S H (2012) A systemic review of the efficacy of interventions for dynamic intermittent dorsal displacement of the soft palate. Equine Vet J 44 (3), 259-266 PubMed.
- Strand E et al (2012) Relative prevalence of upper respiratory tract obstructive disorders in two breeds of harness racehorses (185 cases: 1998-2006). Equine Vet J 44 (5), 518-523 PubMed.
- O'Neill H & Giorio M E (2010) Obstructive lesions of the equine upper respiratory tract Part 2: Surgical options and expected outcomes: Part 2. UK Vet 15 (5), 4-6 VetMedResource.
- Barakzai S Z, Boden L A, Hillyer M H et al (2009) 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 41 (1), 65-69 PubMed.
- Ortvet K F et al (2009) Successful treatment of persistent dorsal displacement of the soft palate and evaluation of laryngohyoid position in 15 racehorses. Equine Vet J 42 (1), 23-29 PubMed.
- Cheetham J, Pigott J H, Thorson L M et al (2008) Racing performance following the laryngeal tie-forward procedure: A case-controlled study. Equine Vet J 40 (5), 501-507 PubMed.
- Franklin S H (2008) Dynamic collapse of the upper respiratory tract: A review. Equine Vet Educ 20 (4), 212-224 VetMedResource.
- Reardon R J M, Fraser B S L, Heller J et al (2008) The use of race winnings, ratings and a performance index to assess the effect of thermocautery of the soft palate for treatment of horses with suspected intermittent dorsal displacement. A case-control study in 110 racing Thoroughbreds. Equine Vet J 40 (5), 508-517 PubMed.
- Barakzai S Z & Dixon P M (2005) Conservative treatment for thoroughbred racehorses with intermittent dorsal displacement of the soft palate. Vet Rec 157 (12), 337-340 PubMed.
- Greet T R C & Dixon P M (2005) 'Flapping like a sail in the breeze': the history of equine soft palate displacement and its treatment. Equine Vet J 37 (5), 386-388 PubMed.
- Woodie J B et al (2005) 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 37 (5), 418-423 PubMed.
- Woodie J B et al (2005) Can an external device prevent dorsal displacement of the soft palate during strenuous exercise? Equine Vet J 37 (5), 425-429 PubMed.
- Barakzai S Zetal (2004) Assessment of the efficacy of composite surgery for the treatment of dorsal displacement of the soft palate in a group of 53 racing Thoroughbreds (1990-1996). Equine Vet J 36 (2), 175-179 PubMed.
- Tulleners E et al (1997) Epiglottic augmentation for treatment of dorsal displacement of the soft palate in racehorses - 59 cases (1985-1994). JAVMA 211, 1022-1028 PubMed.
- Anderson J D et al (1995) Sternothyrohyoideus myectomy or staphylectomy for treatment of intermittent dorsal displacement of the soft palate in racehorses - 209 cases (1986-1991). JAVMA 206, 1909-1912 PubMed.
Other sources of information
- Ducharme N & Cheetham J (2019) Pharynx. In: Equine Surgery. 5th edn. Eds: Auer J & Stick J. Saunders, USA. pp 710-733.
- Smith J J & Embertson R M (2003) Sternothyroideus Myotomy, Staphylectomy and Soft Palate Thermoplasty for Treatment of Dorsal Displacement. In: Proc 49th AAEP Convention. pp 377-380.
- Hackett R P (1998) Soft Palate Displacement. In: Proc World Equine Airway Symposium.