Etiology

Potential causes of laryngeal paralysis are listed in Box 18-1. Laryngeal paralysis is most often idiopathic. Trauma or neoplasia involving the ventral neck can damage the recurrent laryngeal nerves directly or through inflammation and scarring. Masses or trauma involving the anterior thoracic cavity can also cause damage to the recurrent laryngeal nerves as they course around the subclavian artery (right side) or ligamentum arteriosum (left side). Dogs with polyneuropathy-polymyopathy can be presented with laryngeal paralysis as the predominant clinical sign. Polyneuropathies in turn have been associated with immune-mediated diseases, endocrinopathies, or other systemic disorders (see Chapter 71). Congenital laryngeal paralysis has been documented in the Bouvier des Flandres and is suspected in Siberian Huskies and Bull Terriers. A laryngeal paralysis-polyneuropathy complex has been described in young Dalmations, Rottweilers, and Great Pyrenees. Anecdotally, there may be an increasing incidence of idiopathic laryngeal paralysis in older Golden and Labrador Retrievers, and in one study 47 of 140 dogs (34%) with laryngeal paralysis were Labrador Retrievers (MacPhail et al., 2001). Laryngeal paralysis is uncommon in cats.

Clinical Features

Laryngeal paralysis can occur at any age and in any breed, although the idiopathic form is most commonly seen in older large-breed dogs. Clinical signs of respiratory distress and stridor are a direct result of narrowing of the airway at the arytenoid cartilages and vocal folds. The owner may also note a change in voice (i.e., bark or meow). Most patients are presented for acute respiratory distress, in spite of the chronic, progressive nature of this disease. Decompensation is frequently a result of exercise, excitement, or high environmental temperatures, resulting in a cycle of increased respi ratory efforts; increased negative airway pressures, which suck the soft tissue into the airway; and pharyngeal edema and inflammation, which lead to further increased respiratory efforts. Cyanosis, syncope, and death can occur. Dogs with respiratory distress require immediate emergency therapy.

Some dogs with laryngeal paralysis exhibit gagging or coughing with eating or have overt aspiration pneumonia, presumably resulting from concurrent pharyngeal dysfunction or a more generalized polyneuropathy-polymyopathy.

Diagnosis

A definitive diagnosis of laryngeal paralysis is made through laryngoscopy (see p. 239). Movement of the arytenoid cartilages is observed during a light plane of anesthesia while the patient is taking deep breaths. In laryngeal paralysis the arytenoid cartilages and vocal folds remain closed during inspiration and open slightly during expiration. The larynx does not exhibit the normal coordinated movement associated with breathing, opening on inspiration and closing on expiration. Additional laryngoscopic findings may include pharyngeal edema and inflammation. The larynx and pharynx are also examined for neoplasia, foreign bodies, or other diseases that might interfere with normal function and for laryngeal collapse (see p. 241).

Once a diagnosis of laryngeal paralysis is established, additional diagnostic tests should be considered to identify underlying or associated diseases, to rule out concurrent pulmonary problems (e.g., aspiration pneumonia) that may be contributing to the clinical signs, and to rule out concurrent pharyngeal and esophageal motility problems (Box 18-2). The latter is especially important if surgical correction for the treatment of laryngeal paralysis is being considered. If the diagnostic tests fail to identify a cause, idiopathic laryngeal paralysis is diagnosed.

Treatment

In animals with respiratory distress, emergency medical therapy to relieve upper airway obstruction is indicated (see Chapter 26). Following stabilization and a thorough diagnostic evaluation, surgery is usually the treatment of choice. Even when specific therapy can be directed at an associated disease (e.g., hypothyroidism), complete resolution of clinical signs of laryngeal paralysis is rarely seen. Also, most cases are idiopathic, and signs are generally progressive.

Various laryngoplasty techniques have been described, including arytenoid lateralization (tie-back) procedures, partial laryngectomy, and castellated laryngoplasty. The goal of surgery is to provide an adequate opening for the flow of air but not one so large that the animal is predisposed to aspiration and the development of pneumonia. Several operations to gradually enlarge the glottis may be necessary to minimize the chance of subsequent aspiration. The recommended initial procedure for most dogs and cats is unilateral arytenoid lateralization.

If surgery is not an option, medical management consisting of antiinflammatory doses of short-acting glucocorticoids (e.g., prednisone, 0.5 mg/kg given orally q12h initially) and cage rest may reduce secondary inflammation and edema of the pharynx and larynx and enhance airflow.

Prognosis

The overall prognosis for dogs with laryngeal paralysis treated surgically is fair to good. As many as 90% of owners of dogs with laryngeal paralysis that underwent unilateral arytenoid lateralization consider the procedure successful 1 year or longer after surgery (White, 1989; Hammel et al., 2006). MacPhail et al. (2001) reported a median survival time of 1800 days (nearly 5 years) for 140 dogs that underwent various surgical procedures, although the mortality rate from postoperative complications was high at 14%. The most common complication is aspiration pneumonia. A guarded prognosis is warranted for patients with signs of aspiration, dysphagia, megaesophagus, or systemic polyneuropathy or polymyopathy. Dogs with laryngeal paralysis as an early manifestation of generalized polyneuropathy or polymyopathy may have progression of signs.

Clinical Features

The abnormalities associated with the brachycephalic airway syndrome impair the flow of air through the extrathoracic (upper) airways and cause clinical signs of upper airway obstruction, including loud breathing sounds, stertor, increased inspiratory efforts, cyanosis, and syncope. Clinical signs are exacerbated by exercise, excitement, and high environmental temperatures. The increased inspiratory effort commonly associated with this syndrome may cause secondary edema and inflammation of the laryngeal and pharyngeal mucosae and enhance eversion of the laryngeal saccules or laryngeal collapse, further narrowing the glottis, exacerbating the clinical signs, and creating a vicious cycle. As a result, some dogs may be presented with life-threatening upper airway obstruction that requires immediate emergency therapy. Concurrent gastrointestinal signs are commonly reported.

Diagnosis

A tentative diagnosis is made on the basis of the breed, clinical signs, and the appearance of the external nares (Fig. 18-2). Stenotic nares are generally bilaterally symmetric, and the alar folds may be sucked inward during inspiration, thereby worsening the obstruction to airflow. Laryngoscopy (see Chapter 17) and radiographic evaluation of the trachea (see Chapter 20) are necessary to fully assess the extent and severity of abnormalities. Most other causes of upper airway obstruction (see Chapter 26, and Boxes 16-1 and 16-2) can also be ruled in or out on the basis of the results of these diagnostic tests.

FIG 18-2 Cat with severely stenotic nares (A), as compared with the nares of a normal cat (B). Early correction of stenotic nares and other amenable upper airway obstructions, such as an elongated soft palate, is highly recommended.

Treatment

Therapy should be designed to enhance the passage of air through the upper airways and to minimize the factors that exacerbate the clinical signs (e.g., excessive exercise and excitement, overheating). Surgical correction of the anatomic defects is the treatment of choice. The specific surgical procedure selected depends on the nature of the existing problems and can include widening of the external nares and removal of excessive soft palate and everted laryngeal saccules.

Correction of stenotic nares is a simple procedure and can lead to a surprising alleviation of the signs in affected patients. Stenotic nares can be safely corrected at 3 to 4 months of age, ideally before clinical signs develop. The soft palate should be evaluated at the same time and also corrected if elongated. Such early relief of obstruction should decrease the amount of negative pressure placed on the pharyngeal and laryngeal structures during inspiration and decrease progression of disease.

Medical management consisting of the administration of short-acting glucocorticoids (e.g., prednisone, 0.5 mg/kg given orally q12h initially) and cage rest may reduce the secondary inflammation and edema of the pharynx and larynx and enhance airflow, but it will not eliminate the problem. Emergency therapy may be required to alleviate the upper airway obstruction in animals presenting in respiratory distress (see Chapter 26).

Weight management and concurrent treatment for gastrointestinal disease should not be neglected in patients with brachycephalic airway syndrome.

Prognosis

The prognosis depends on the severity of the abnormalities at the time of diagnosis and the ability to surgically correct them. The clinical signs will progressively worsen if the underlying problems go uncorrected. The prognosis after early surgical correction of the abnormalities is good for many animals. Laryngeal collapse (see p. 241) is generally considered a poor prognostic indicator, although a recent study demonstrated that even dogs with severe laryngeal collapse can respond well to surgical intervention (Torrez et al., 2006). Permanent tracheostomy can be considered as a salvage procedure in animals with severe collapse that are not responsive. A hypoplastic trachea is not surgically correctable, but there is no clear relationship between the degree of hypoplasia and morbidity or mortality.

Clinical Features

The clinical signs of laryngeal neoplasia are similar to those of other laryngeal diseases and include noisy respiration, stridor, increased inspiratory efforts, cyanosis, syncope, and a change in bark or meow. Mass lesions can also cause concurrent dysphagia, aspiration pneumonia, or visible or palpable masses in the ventral neck.

Diagnosis

Extralaryngeal mass lesions are often identified by palpation of the neck. Primary laryngeal tumors are rarely palpable and are best identified by laryngoscopy. Laryngeal radiographs, ultrasonography, or computed tomography can be useful in assessing the extent of disease. Differential diagnoses include obstructive laryngitis, nasopharyngeal polyp, foreign body, traumatic granuloma, and abscess. For a definitive diagnosis of neoplasia to be made, histologic examination of a biopsy specimen of the mass must be done. A diagnosis of malignant neoplasia should not be made on the basis of the gross appearance alone.

Treatment

The therapy used depends on the type of tumor identified histologically. Benign tumors should be excised surgically, if possible. Complete surgical excision of malignant tumors is rarely possible, although ventilation may be improved and time may be gained to allow other treatments such as radiation or chemotherapy to become effective. Complete laryngectomy and permanent tracheostomy may be considered in select animals.

Prognosis

The prognosis in animals with benign tumors is excellent if the tumors can be totally resected. Malignant neoplasms are associated with a poor prognosis.