Equis ISSN 2398-2977

Soft palate: dorsal displacement

Synonym(s): Choking down, DDSP

Contributor(s): Debbie Archer, Patrick Colahan, Paddy Dixon, Huw Llewellyn, Vetstream Ltd

Introduction

  • Abnormal position of soft palate and larynx during maximum physical exertion.
  • Performance limiting condition in the equine athlete.
  • Cause: idiopathic or secondary to many possible underlying causes.
  • Signs: can cause severe respiratory obstruction; respiratory noise together with a dramatic drop in exercise tolerance; variable drop in performance associated with acute dyspnea; characteristic gurgling noise.
  • Diagnosis: history, signs, endoscopy at rest and on high speed treadmill.
  • Treatment: conservative or surgical treatments. No one treatment favored over the other - success rates approximately 60% regardless of surgical procedure performed.
  • Prognosis: guarded.

Pathogenesis

Etiology

  • Idiopathic: neuromuscular dysfunction or inco-ordination 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

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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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • 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 J44(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 J44(5), 518-523 PubMed
  • Barakzai S Z & Hawkes C S (2010)Dorsal displacement of the soft palate and palatal instability.Equine Vet Educ 22(5), 253-264 VetMedResource
  • 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 Vet15(5), 4-6 VetMedResource.
  • Pigott J Het al(2010)Incidence of swallowing during exercise in horses with dorsal displacement of the soft palate.Equine Vet J42(8), 732-737 PubMed.
  • Barakzai S Z, Finnegan C, Dixon P M, Hillyer M H & Boden L A (2009)Use of tongue ties in Thoroughbred racehorses in the United Kingdom, and its association with surgery for dorsal displacement of the soft palate.Vet Rec165(10), 278-281 PubMed.
  • Barakzai S Z, Boden L A, Hillyer M H, Marlin D J & Dixon P M (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 J41(1), 65-69 PubMed.
  • Ortvet K Fet al(2009)Successful treatment of persistent dorsal displacement of the soft palate and evaluation of laryngohyoid position in 15 racehorses.Equine Vet J42(1), 23-29 PubMed.
  • Cheetham J, Pigott J H, Thorson L M, Mohammed H O & Ducharme N G (2008)Racing performance following the laryngeal tie-forward procedure: A case-controlled study.Equine Vet J40(5), 501-507 PubMed.
  • Franklin S H (2008)Dynamic collapse of the upper respiratory tract: A review.Equine Vet Educ20(4), 212-224 VetMedResource.
  • Reardon R J M, Fraser B S L, Heller J, Lischer C, Parkin T & Bladon B M (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 Throughbreds.Equine Vet J40(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 Rec157(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 J37(5), 386-388 PubMed.
  • Woodie J Bet 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 J37(5), 418-423 PubMed.
  • Woodie J Bet al(2005)Can an external device prevent dorsal displacement of the soft palate during strenuous exercise?Equine Vet J37(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 J36(2), 175-179 PubMed.
  • Tulleners Eet al(1997)Epiglottic augmentation for treatment of dorsal displacement of the soft palate in racehorses - 59 cases (1985-1994).JAVMA211, 1022-1028 PubMed.
  • Anderson J Det al(1995)Sternothyrohyoideus myectomy or staphylectomy for treatment of intermittent dorsal displacement of the soft palate in racehorses - 209 cases (1986-1991).JAVMA206, 1909-1912 PubMed.
  • Dugdale D J & Greenwood R E S (1993)Some observations on conservative techniques for treating laryngopalatal dislocation (dorsal displacement of the soft palate) in the horse.Equine Vet Educ5(4), 177-180 VetMedResource.

Other sources of information

  • 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.


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