Laryngeal Paralysis

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Introduction

The larynx functions to regular airflow and voice production and to prevent inhalation of food. The arytenoid cartilages of the larynx abduct at each inspiration, and are controlled by the dorsal cricoarytenoid muscles. These are innervated by the recurrent laryngeal nerve.

Lesions to this nerve or to the muscle result in laryngeal paralysis, which can be unilateral or bilateral. The flaccid arytenoid cartilage is sucked into the laryngeal lumen during inspiration, leading to an inspiratory dyspnoea.

Congenital and acquired forms have been recognised in dogs and cats:

Congenital laryngeal paralysis: reported in the Bouvier des Flandres, Bull Terriers, Dalmatians, Rottweilers and Huskies.

There is Wallerian degeneration of the recurrent laryngeal nerve and abnormalities of the nucleus ambiguus.

The disease appears before 1 year of age, earlier than in dogs with the acquired form.

Acquired laryngeal paralysis: most common in large breed dogs such as Labradors, St Bernards, Irish Setters over the age of 9. It has also been reported in cats. It occurs three times more commonly in males than in females.

The most common cause is idiopathic, but other causes include: trauma, neck surgery (thyroidectomies in cats), cranial mediastinal or neck mass, hypothyroidism causing a polyneuropathy and polymyopathy.

Clinical Signs

Clinical signs progress slowly.

Early signs include: change in voice, gagging and coughing during eating and drinking, exercise intolerance, laryngeal stridor.

There may be episodes of severe dyspnoea, cyanosis and collapse.

Animals present with an inspiratory dyspnoea that is not alleviated by mouth-breathing.

Aspiration pneumonia may be present as coughing, pyrexia and consolidation of the cranial lung fields on auscultation.

Diagnosis

Clinical signs and presentation are suggestive.

Radiography is essential to evaluate the lungs, as aspiration pneumonia is common.

Laryngeal examination is the definitive method of diagnosis. A light plane of anaesthesia should be used so as not to inhibit laryngeal function further. Motion of the arytenoid cartilages is observed during inspiration. In laryngeal paralysis the arytenoid cartilages and the vocal folds are immobile and drawn towards the midline during inspiration. In unilateral cases, only one side does not move.

There may be oedema and erythema of the cartilages due to repeated trauma during respiration.

Treatment

Emergency treatment: animals are usually presented in a state of collapse and cyanosis. Corticosteroids can be given to reduce airway inflammation and oedema, and oxygen should be provided by mask or oxygen cage.

Cooling and sedation with acepromazine may also be effective if the animal is hot and stressed.

An emergency tracheostomy may have to be performed if the animal deteriorates further.

Surgical correction:

Unilateral or bilateral arytenoid lateralisation: this is the most common surgical approach. Unilateral lateralisation is sufficient to treat signs of laryngeal paralysis. Aspiration pneumonia is a complication of surgery, and occurs more frequently if bilateral lateralisation is performed. Therefore the bilateral technique should only be used if the unilateral technique does not resolves the clinical signs.
Partial laryngectomy: ventriculocordectomy and partial arytenoidectomy through the oral or ventral approach. There is a risk of haemorrhage and inflammation with this procedure, and aspiration pneumonia results if too much of the larynx is excised.
Modified castellated laryngofissure: through a stepped incision into the thyroid cartilage, resection of the vocal folds and stabilisation of the arytenoid cartilages. This requires a temporary tracheostomy tube for 3-4 days post-operatively, and aspiration pneumonia, oedema and stenosis can occur.
Permanent tracheostomy: to bypass the upper airway obstruction. This may be indicated in dogs at high risk of developing aspiration pneumonia due to megaoesophagus or myopathies.

The technique of choice is usually unilateral arytenoid lateralisation, but the choice may be determined by the size of the animal, the severity of the obstruction and the preference of the surgeon.

Prognosis

The prognosis is reasonably good provided there is no significant underlying disease process.

The risk of aspiration pneumonia can be managed by feeding larger pieces of food, slowly and with a raised bowl.


Laryngeal Paralysis Learning Resources
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Flashcards
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Small Animal Soft Tissue Surgery Q&A 22

Larynx Pathology Flashcards


References

Slatter, D. (2002) Textbook of small animal surgery Elsevier Health Sciences

Merck and Co (2008) Merck Veterinary Manual Merial

Norsworthy, G. (2010) The Feline Patient Wiley-Blackwell




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