Equine laryngeal dysplasia is a congenital syndrome recognized in horses of various breeds. Also referred to as 4th branchial arch disease (4-BAD), this syndrome involves developmental malformation of laryngeal structures formed from the 4th and, occasionally 6th, branchial arches. Aplasia or hypoplasia of various laryngeal structures may occur unilaterally or bilaterally but defects are most often right-sided. Numerous developmental abnormalities involving the cricoid and thyroid cartilages and pharyngeal muscles have been identified.
Developmental anomalies most often include:
Malformations of thyroid and cricoid cartilages
Absent crico-thyroid and crico-arytenoid articulations
Hypoplasia or aplasia of the cricothyroideus or cricopharyngeus muscles
Malformation of upper esophageal sphincter muscles
Clinical signs of laryngeal dysplasia can first occur in foals or adult horses, with the severity of clinical signs dependent upon the extent of the defect, specific structures affected, and the use of the horse. The most common clinical sign is respiratory noise during exercise, although dyspnea, exercise intolerance, dysphagia, and mild eructation or colic (secondary to aerophagia) are reported. In some horses, laryngeal dysplasia is diagnosed as an incidental finding.
Diagnosis can often be made via laryngeal palpation and endoscopy (rest or dynamic). Dynamic endoscopy is essential for assessing laryngeal function during exercise and for prognostic and treatment decisions. Laryngeal ultrasound or radiography are useful in confirming the diagnosis. CT or MRI are the most accurate diagnostic tool.
Diagnostic findings can include:
Palpation of the larynx consistent with an absent cricothyroid articulation—palpable space between the cricoid and thyroid cartilages; absence of one or both wings of the thyroid cartilage
Endoscopic examination at rest or dynamic—reduced right-sided arytenoid abduction (most common), vocal fold collapse, rostral displacement of the palatopharyngeal arch, and aryepiglottic fold collapse
Radiography—dilation of the cricopharynx with a continuous column of air from the pharynx to the cervical esophagus
Laryngeal ultrasonography—absent cricothyroid articulation, dorsal extension of thyroid cartilage
Numerous surgical treatment approaches have been proposed and include ventriculocordectomy, arytenoidectomy, laryngoplasty, and laser thermoplasty. Choice of treatment and outcome depend on the nature and severity of structural abnormalities and goals for athletic performance. In general, affected horses are unlikely to become effective athletes.
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Also see pet health content regarding laryngeal dysplasia in horses Disorders of the Larynx in Horses The larynx is the part of the throat often called the “voice box” in humans. It is located near the top of the trachea. The larynx is composed of muscles and cartilage, and it includes the vocal... read more .