Dorsal Displacement of Soft Palate

Also known as: DDSP

Introduction

Dorsal displacement of the soft palate is a performance-limiting condition of the upper respiratory tract and is a relatively common cause of upper respiratory noise during exercise.

During DDSP, the caudal free margin of the soft palate moves dorsal to the epiglottis, creating a functional obstruction within the airway.

DDSP can be persistent or, more commonly, intermittent.

Horses with persistent disease present with severe exercise intolerance and respiratory noise. There may be concurrent epiglottic entrapment or neurological deficits.

Intermittent DDSP arises as an acute respiratory obstruction that occurs during fast exercise. The condition can occur secondary to other conditions, and may be a symptom rather than a disease in its own right.

Underlying causes include:

Conditions causing fatigue: unthriftiness, primary cardiovascular disorders, primary pulmonary diseases like small airway inflammation, recurrent laryngeal neuropathy

Disorders of the palate: congenital or iatrogenic defects, ulceration of the free border, intrapalatal cysts, pharyngeal paralysis

Disorders of the epiglottis: hypoplasia, deformity, entrapment, subepiglottic cysts, epiglottitis

Conditions causing mouth breathing: neglected dental disease, retained caps, harsh bit

Conditions provoking pharyngeal discomfort: pharyngeal lymphoid hyperplasia, pharyngitis, pharyngeal cysts, upper respiratory tract infections, neoplasia

Neuromuscular dysfunction: extrinsic or intrinsic muscles controlling soft palate position dysfunction

Clinical Signs

Intermittent DDSP occurs during exercise. It causes a loud vibrant noise, described as 'gurgling' and an interference with the progress of the horse, 'choking up' or 'choking down'. The horse often loses its stride completely as it gulps and attempts to restore the larynx to the intranarial position. As soon as the normal anatomical configuration is restored, the horse will appear normal and it can resume galloping.

DDSP usually occurs when the horse reaches the point of maximal exertion, usually in the later stages of a race.

Billowing of the cheeks may also be observed.

Diagnosis

This is based on the history and clinical signs.

Endoscopic examination at rest may enable a diagnosis to be made, however as the condition is intermittent the horse may appear normal.

The gold standard is an exercising endoscopic examination using a treadmill or remote endoscopy is now also available.

Tracheal washings samples can be taken and examined by cytology and culture to find any underlying inflammation or infection.

Treatment

The most effective treatment in young horses and horses with evidence of upper respiratory tract infection is rest and anti-inflammatory therapy.

Tack modifications such as tongue ties and figure of eight nosebands are traditional ways of reducing the occurrence of DDSP, but there is no scientific evidence to support their use.

Surgical treatment alternatives are numerous and include:

staphylectomy: trimming the caudal free margin of the soft palate

myectomy and tenectomy procedures

epiglottic augmentation

thermal and laser procedures to cauterise the soft palate

laryngeal tie-forward

The results of the surgical treatments are unpredictable, but may be successful in approximately 50% of cases.

Laryngeal tie-forward has been found to have the best prognosis for improved racing performance.

Dorsal Displacement of Soft Palate Learning Resources
Flashcards Test your knowledge using flashcard type questions	Nasopharynx Pathology Flashcards Equine Internal Medicine Q&A 07

References

McGorum, B. (2007) Equine respiratory medicine and surgery Elsevier Health Sciences

Rush, B. (2004) Equine Respiratory Diseases John Wiley and Sons

Merck and Co (2008) The Merck Veterinary Manual Merial