Dorsal Displacement of the Soft Palate (DDSP)

Outline

Overview
Signalment
Signs
Causes and Risk Factors

BASICS

Overview

When the soft palate displaces dorsally, the epiglottis cannot be seen within the nasopharynx as it is in the oropharynx
During exhalation, the caudal free margin of the soft palate billows across the rima glottis, creating an airway obstruction during exhalation
DDSP has been estimated to affect 10% of racehorses
This condition may be intermittent at exercise or permanent

Signalment

The most common presentation is intermittent and is seen predominantly in racehorses and to a lesser degree in sport horses.

Signs

Intermittent DDSP occurs during exercise
Usually associated with an abnormal upper respiratory noise during exhalation, often referred to as “gurgling noise”
Approximately 10–20% of horses with DDSP do not make a noise and are referred to as “silent displacers”
Horses with intermittent DDSP generally have a history of exercise intolerance and may make a “gurgling” noise during exhalation; concurrent with these signs is open-mouth breathing

Causes and Risk Factors

The causes can be classified into 2 groups. (1) Intrinsic causes associated with structural abnormality such as subepiglottic cyst, subepiglottic masses, epiglottic cartilage deformity, epiglottitis, and palatal cyst or inflammation. It can also be due to decreased muscular activity of the palatinus and palatopharyngeus muscles. It may also be due to heightened sensory input of the larynx, as seen with painful conditions. (2) Extrinsic causes are those associated with factors affecting neuromuscular control of the position of the basihyoid bone and/or larynx.

Diagnosis ⬆ ⬇

Outline

Differential Diagnosis
Imaging
Other Diagnostic Procedures

DIAGNOSIS

Differential Diagnosis

Epiglottic entrapment.

Imaging

Lateral radiographs of the larynx/pharynx allow identification of soft palate displacement, the length of the epiglottic cartilage, and presence of subepiglottic and palatal cysts/mass. However, these findings are more easily assessed by endoscopy.

Other Diagnostic Procedures

The diagnosis of intermittent DDSP is based on a history of a sudden decrease in performance in the second half of the exercise intensity or competition and generally is associated with “gurgling” expiratory respiratory noises
Palatal instability at exercise is seen as a prodromal sign of DDSP
Endoscopy of the upper airway at rest usually is normal but may identify structural anomalies and the presence of an ulcer on the caudal edge of the soft palate
There is a poor correlation with the observation of DDSP at rest and during exercise
The best diagnostic test is dynamic endoscopy (overground or treadmill)

Treatment ⬆ ⬇

TREATMENT

Treatment initially is directed at modifying or eliminating factors associated with the occurrence of DDSP
The incidence of intermittent DDSP decreases with maturity
If upper respiratory tract inflammation was diagnosed during the examination, treatment should include judicious use of systemic anti-inflammatory medication
Several surgical therapies and combination surgical therapies currently are performed as treatment. Certain procedures (laser or cautery-assisted treatment of the soft palate, staphylectomy, or surgical imbrication of the palate) attempt to “stiffen” the soft palate or reduce its obstructive surface (staphylectomy); there is a lack of evidence-based data in support of persistent stiffening or fibrosis being induced. Other techniques such as myectomies (sternothyroid and/or sternohyoid muscle resection) and surgical repositioning of the larynx in a dorsal and forward position (laryngeal tie-forward) are thought to optimize the position of the larynx during exercise. The latter 2 techniques (laryngeal tie-forward and sternothyroid muscles) are generally combined

Medications ⬆ ⬇

Outline