August 1, 2017
Laryngeal paralysis is a manifestation of a polyneuropathy seen mostly in older large breed dogs; it is occasionally diagnosed in young dogs (less than a year of age) of certain breeds such as Siberian Huskies, Bouviers, Rottweilers, and others. In the summer months, we often see an increase in these cases due to the high temperatures, increased outdoor exercise, and other seasonal stressors.
ACQUIRED LARYNGEAL PARALYSIS
The acquired form is commonly seen in Golden Retrievers, Labs, and occasionally small breeds or cats. In most cases, it is idiopathic; though, occasionally has been associated with hypothyroidism and neck surgery (damage to the recurrent laryngeal nerve during tumor dissection). Diseases that mimic laryngeal paralysis are much less common but include laryngeal neoplasia, granulomatous laryngitis and pharyngeal masses or neoplasia.
Disease progression is typically slow (months to a year or two) but acute signs of significant respiratory distress can be unexpectedly triggered by any form of stress; commonly high ambient temperatures, excitement, exercise or anxiety induced stress, or anything that leads to severe panting.
The disease should be thought of as a generalized polyneuropathy that usually manifests with laryngeal signs first. These include stridor, dysphonia, gagging, exercise intolerance, progressive anxiety and later cyanosis and collapse. In the summer months, many of these patients are hyperthermic and the excessive panting overwhelms the struggling larynx. Some patients will also have more generalized signs such as regurgitation and ataxia. It is important to identify these signs as there is no treatment for the polyneuropathy per se.
We have performed nerve conduction studies in patients whose only signs are related to laryngeal function and proven that the disease in these individuals is generalized despite the absence of other clinical signs. The age of onset is probably a contributing factor here. Most cases of laryngeal paralysis seem to be in dogs between 11-13-years-old. There is probably not enough time for generalized signs to develop given their advanced age. This should be discussed with owners of younger dogs exhibiting signs of laryngeal paralysis.
Patients who present with severe acute respiratory distress are treated with sedation (usually acepromazine because of its longer duration of action), steroids and oxygen therapy (preferably nasal or nasopharyngeal in dogs over 45 lb). Chest radiography should be done when it is safe to do so as these patients are at risk for aspiration pneumonia and occasionally present with this complication.
When the patient has been stabilized, we usually perform unilateral arytenoid lateralization (“tieback”) after documenting abnormal adduction of the arytenoid(s) with light propofol anesthesia. If in doubt, a test dose of Dopram (2.2 mg/kg IV) can be given to stimulate inspiration. Marginal laryngeal function will usually deteriorate under this test. Sometimes the stimulation will lighten anesthetic depth so it is important to be ready for this. The patient is then fully anesthetized, intubated and prepped for surgery. While there is not much objective data on efficacy, we typically premed these patients with metoclopramide and maropitant to decrease risks of regurgitation during and after surgery.
Surgical outcomes are generally good and most of these patients return to a good quality of life. The main postoperative complication is aspiration pneumonia. While not common, we do see it from time to time and it can be life-threatening in some cases. At the very least, it complicates recovery and increases cost for the owner. I explain to owners that (for the rest of their pet’s life) they should keep their dog on a leash (with a harness), not allow swimming, and avoid stressful activities including exposure to high temperatures.
Laryngeal paralysis in brachycephalic breeds (brachycephalic airway syndrome, BAS) is a different disease with different management and outcomes. BAS usually consists of stenotic nares, elongated soft palate, and with time, progressive laryngeal collapse. Many of these dogs also have distal esophageal abnormalities with a history of regurgitation, esophagitis, and a predisposition to aspiration pneumonia, particularly as their laryngeal function deteriorates. Laryngeal collapse occurs because of progressive chondromalacia caused by chronic airway stress.
There are 3 stages: Stage I, laryngeal saccule eversion (very common even in young dogs with an elongated soft palate), stage II, softness and medial displacement of the cuneiform process, and stage III, collapse of the corniculate process with airway obstruction. We see Stages II and III in slightly older dogs to middle aged dogs. It is a common reason for sudden deterioration in airway function in a 7-year- old English Bulldog.
ASSESSMENT & MANAGEMENT
These dogs present with severe stertor, gagging, exercise intolerance, cyanosis, and dyspnea. They usually have a long history of milder stertor, snoring while asleep etc. Some patients have hypoplastic tracheas and all are at risk for aspiration pneumonia. Management of early cases involves correction of the nares, soft palate, and saccules. Weight and exercise control may also be of value. Acute respiratory distress is handled as described earlier. More advanced cases of laryngeal collapse (stages II and III) generally do not do well with surgery. Laryngeal tieback in a patient with chondromalacia will likely be disappointing and a partial laryngectomy risks aspiration pneumonia and laryngeal web formation. A permanent tracheostomy may be temporarily useful in some dogs but those breeds with very loose pendulous skin (English Bulldogs especially) may have problems. The key in management is to encourage owners of young dogs showing early signs to have surgical correction of the problems that can be helped.