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

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Larynx Pathology Flashcards