Page 305 - Small Animal Internal Medicine, 6th Edition

CHAPTER 18
VetBooks.ir

Disorders of the Larynx

and Pharynx

LARYNGEAL PARALYSIS ventral neck can damage the recurrent laryngeal nerves
directly or through inflammation and scarring. Masses or
Laryngeal paralysis refers to failure of the arytenoid carti- trauma involving the anterior thoracic cavity can also cause
lages to abduct during inspiration, creating extrathoracic damage to the recurrent laryngeal nerves as they course
(upper) airway obstruction. The abductor muscles are inner- around the subclavian artery (right side) or the ligamentum
vated by the left and right recurrent laryngeal nerves. If arteriosum (left side). These causes are less commonly
clinical signs develop, both arytenoid cartilages are usually encountered.
affected. The disease can affect dogs and cats, but dogs are
more often presented with clinical signs. Clinical Features
Laryngeal paralysis can occur at any age and in any breed,
Etiology although it is most commonly seen in older large-breed dogs.
Potential causes of laryngeal paralysis are listed in Box 18.1, Labrador Retrievers are overrepresented. The disease is
with the cause remaining idiopathic in most cases. Histori- uncommon in cats. Clinical signs of respiratory distress and
cally, dogs with idiopathic laryngeal paralysis were consid- stridor are a direct result of narrowing of the airway at the
ered to have dysfunction limited to the laryngeal nerve. It is arytenoid cartilages and vocal folds. The owner may also
now believed that idiopathic laryngeal paralysis is part of a note a change in voice (i.e., bark or meow). Many patients
generalized neuromuscular disorder. A study by Stanley are presented for acute respiratory distress, in spite of the
et al. (2010) demonstrated that dogs with idiopathic laryn- chronic, progressive nature of this disease. Decompensation
geal paralysis have esophageal dysfunction detected by swal- occurs as a result of exercise, excitement, or high environ-
lowing studies. This study further showed that, on the basis mental temperatures, resulting in a cycle of increased respi-
of neurologic examination, these dogs will demonstrate signs ratory efforts; increased negative airway pressures, which
of generalized neuromuscular disease within a year. Abnor- suck the soft tissue into the airway; and pharyngeal edema
mal electrodiagnostic testing and histologic changes in and inflammation, which lead to further increased respira-
peripheral nerves have also been reported (Thieman et al., tory efforts. Cyanosis, syncope, and death can occur. Dogs
2010). Dogs with overt polyneuropathy-polymyopathy also in respiratory distress require immediate emergency therapy.
may present with laryngeal paralysis as the predominant Some dogs with laryngeal paralysis exhibit gagging or
clinical sign. Polyneuropathies in turn have been associated coughing, often noted particularly with eating or drinking.
with immune-mediated diseases, endocrinopathies, or other These signs could be a result of secondary laryngitis, concur-
systemic disorders (see Chapter 66). rent pharyngeal or esophageal dysfunction, and/or esopha-
Congenital laryngeal paralysis has been documented in geal reflux secondary to upper airway obstruction. Signs of
the Bouvier des Flandres and is suspected in Siberian Huskies aspiration pneumonia may also be present but are rarely the
and Bull Terriers. A laryngeal paralysis-polyneuropathy presenting complaint.
complex has been described in young Dalmatians, Rottwei-
lers, and Great Pyrenees. The possibility that a genetic pre- Diagnosis
disposition exists in Labrador Retrievers, even though signs A definitive diagnosis of laryngeal paralysis is made through
appear later in life, has been proposed on the basis of their laryngoscopy (see Chapter 17). Movement of the arytenoid
overrepresentation in reports of laryngeal paralysis (Shelton, cartilages is observed during a light plane of anesthesia
2010). while the patient is taking deep breaths. In laryngeal paraly-
Direct damage to the laryngeal nerves or the larynx can sis, the arytenoid cartilages and the vocal folds remain in
also result in paralysis. Trauma or neoplasia involving the a midline position or are sucked inward (paradoxically)

277