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
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.
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.
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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