Laryngeal Hemiplegia

• In Horses:
• Unilateral paralysis of arytenoids
• Common 2-13% training thoroughbreds
• Damaged/ dysfunctional recurrent laryngel nerve (branch of vagus)
• Mostly left side affected, occasionally also the right nerve
• Demyelination of nerve fibres, and leading to atrophy of intrinsic laryngeal muscles particularly the adductor (cricoarytenoid) which allows the left arytenoid cartilage to lean into the laryngeal lumen
• The 'roaring' is noticeable after exercising
• The aetiology is not properly established but suggested factors are:
  • Length of the left recurrent nerve
  • Extension neuritis in guttural pouch mycosis
  • Neurotoxins - organophosphorus compounds may produce similar degenerative changes in the nerves
  • Enlarged retropharyngeal lymph nodes
  • Neoplasia
  • Trauma

• These horses are also known as "roarers"
• Equine laryngeal hemiplegia is a very common condition.

Pathogenesis

1. The disease starts with an idiopathic degeneration of the left recurrent laryngeal nerve.
2. This leads to atrophy of the left dorsal cricoarytenoid muscle.
3. Without the use of this muscle, the horse is unable to abduct the left arytenoid cartilage and vocal fold.
4. Airways are therefore partially obstructed on inspiration.

View images courtesy of Cornell Veterinary Medicine

Idiopathic Laryngeal Hemiplegia:

Progressive loss of fibres (esp. large diameter) within left recurrent laryngeal nerve compared to right

Dying back axonopathy with myelin sheath involvement:

Degenerating fibres

Regenerating clusters

De/Re-myelination

Flattening of nerve between aorta & trachea

Inspiratory 'roaring' noise - flapping of vocal fold

'Slap test' - adduction of contralateral arytenoid during expiration

Endoscopic examination - assymetric arytenoids, poor abduction of left vocal fold.

Palpable atrophy of laryngeal musculature

Laryngeal Ventriculectomy (Hobday procedure)

'Tie Back'

Laryngeal muscle prosthesis

Prognosis usually good

Test yourself with the Larynx Pathology Flashcards

Larynx Pathology Flashcards