Introduction

Laryngeal paralysis is caused by a failure of the arytenoid cartilages to abduct during inspiration, causing an airway obstruction. It has been reported in both dogs and cats. Laryngeal paralysis can be congenital or acquired with the latter being the most common. It can be either unilateral or bilateral and results in a partial or complete loss of function of the larynx.¹

Anatomy

The larynx is located immediately cranial to the trachea and is responsible for controlling breathing, vocalization, and protecting the lower airway.¹ It is comprised of several structures, including the laryngeal cartilages (epiglottis, thyroid, cricoid, inter‐arytenoid, sesamoid, and paired arytenoids), vocal folds, and intrinsic and extrinsic musculature. The cricoarytenoideus dorsalis muscle (CAD) is responsible for abducting the arytenoid cartilages to open the glottis during inspiration. This muscle is controlled by the recurrent laryngeal nerves, which originate from the vagus nerve.

Etiology

Congenital laryngeal paralysis can be hereditary or caused by congenital polyneuropathy. Hereditary laryngeal paralysis typically occurs in dogs less than one year old and has been reported in Bouvier de Flandres and Siberian Huskies.² Congenital polyneuropathy causing laryngeal paralysis can also be associated with other clinical signs including hypotonia, hyporeflexia, and diffuse muscle atrophy. It has been reported in several breeds, including Rottweilers, Dalmatians, Bouvier de Flandres, Afghan hounds, and Siberian Huskies.²

Acquired laryngeal paralysis is mostly commonly idiopathic. Canine geriatric onset laryngeal paralysis polyneuropathy (GOLPP), previously known as idiopathic laryngeal paralysis, is a progressive disease that causes degeneration of nerves that control muscles of the larynx, causing paralysis of the larynx via inability to abduct the arytenoid cartilages.^1,3,4 Acquired laryngeal paralysis occurs most commonly in older large‐breed dogs, such as Labrador Retrievers, Golden Retrievers, and St. Bernards. In these cases, laryngeal paralysis is accompanied by esophageal dysfunction (~2/3 cases) and hind end weakness (~1/3 cases).^3,5 The exact cause of GOLPP is unknown, but it is believed to be a combination of environmental and genetic factors.^1,3 Infection, trauma, tumors, iatrogenic causes, and neurological diseases, like myasthenia gravis, can also cause laryngeal paralysis.¹

History and Clinical Findings

Pets with laryngeal paralysis typically present with respiratory stridor, exercise intolerance, and periods of difficulty breathing, especially when the pet is excited or stressed.¹ Exercise intolerance may become more apparent in hot and humid weather, so more cases may present in the spring and summer. In severe cases, a pet may present urgently when they have become cyanotic or experience an episode of collapse, or an owner may report a change in the sound of a bark, hacking, coughing, gagging during eating/drinking, pelvic limb weakness or scuffing of toes, and generalized muscle atrophy.

Diagnostics

Laryngeal paralysis is diagnosed via sedated laryngeal exam. Prior to sedated laryngeal exam, a complete blood count and chemistry profile should be performed. Blood work is typically unremarkable, although an elevated white blood cell count should raise concern for aspiration pneumonia. Thyroid testing should be considered to rule out the cases of laryngeal dysfunction secondary to hypothyroidism. Three‐view thoracic radiographs should also be performed to rule out intrathoracic disease, megaesophagus, aspiration pneumonia, or non‐cardiogenic pulmonary edema.¹ Pre‐operative aspiration pneumonia is associated with an increased risk of postoperative complications, so, if possible, surgery should be delayed until the pneumonia is resolved.

For laryngeal examination, the patient is placed in sternal recumbency and must be under a light plane of anesthesia. It is the author’s preference to administer propofol slowly until the patient allows for opening of the mouth and exam of the larynx without causing apnea, and there are various pre‐medication protocols that exist for administration of other drugs, such as the addition of intravenous midazolam, butorphanol, and/or dexmedetomidine in the editor’s practice. The oral cavity, oropharynx, and larynx should be thoroughly evaluated for any pathology, including masses. Using a laryngoscope or endoscope, the larynx is observed while the patient is breathing. It is important the anesthetist announces when the pet is inspiring during the exam. In a normal dog, the arytenoid cartilages will abduct during inspiration. In a dog with laryngeal paralysis, the arytenoid cartilages can be erythematous, edematous, and ulcerated, and the arytenoid cartilages fail to abduct during inspiration. Paradoxical motion can also be seen, where the arytenoid cartilages are pulled inward, closing the glottis during inspiration, and then return to a neutral position during expiration. Paradoxical motion can be mistaken for normal motion of the arytenoids; therefore, it is important to know the timing of inspiration and expiration to help differentiate. To improve laryngeal motion during the exam, doxapram should be used (dose: 1–1.5 mg/kg IV given quickly).^3,6,7 Please note that it may worsen paradoxical motion or increase occlusion of the glottis.

Treatment

The treatment of laryngeal paralysis can vary from medical management to surgical intervention. Medical management can include weight loss, reduced stress, sedatives, and environmental changes, like avoidance heat and exercise, especially in hot and humid weather. However, when the patient’s quality of life is affected, the symptoms can no longer be managed medically, or the patient experiences a respiratory crisis, surgical intervention is required. If a pet presents in a respiratory crisis, patient stabilization is warranted and includes sedation, patient cooling (if needed), and providing supplemental oxygen either by flow‐by, nasal cannula, oxygen cage, or emergent intubation. In the author’s opinion, a temporary tracheostomy is rarely needed.^1,2

The most common surgical intervention for laryngeal paralysis is a unilateral cricoarytenoid lateralization or “tie‐back” procedure. Other surgical options include bilateral arytenoid lateralization, transoral partial laryngectomy, ventriculocordectomy, partial arytenoidectomy, modified castellated laryngofissure, and permanent tracheostomy.¹

Anesthetic Considerations

It is recommended the patient be pre‐medicated with antacids, anti‐nausea, and promotility medications prior to general anesthesia. Due to the risk for regurgitation and aspiration perioperatively, limited use of opioids is recommended. If opioids are used, it is the author’s preference to use partial mu agonists or rapid‐acting pure mu agonists, such a fentanyl or remifentanil, following intubation. Local incisional blocks using lidocaine or long‐acting liposomal bupivacaine are recommended so that opioids, if used, can be discontinued immediately following surgery.