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- 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
- These horses are also known as "roarers"
- Equine laryngeal hemiplegia is a very common condition.
- The disease starts with an idiopathic degeneration of the left recurrent laryngeal nerve.
- This leads to atrophy of the left dorsal cricoarytenoid muscle.
- Without the use of this muscle, the horse is unable to abduct the left arytenoid cartilage and vocal fold.
- Airways are therefore partially obstructed on inspiration.
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
- 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