Laryngeal paralysis is a congenital or acquired disease that causes upper airway obstruction. Paralysis causes partial or
complete obstruction of the laryngeal lumen due to denervation of the cricoarytenoideus dorsalis muscle of the larynx. Interruption
of nerve transmission from the recurrent laryngeal nerve or the vagus results in failure of the arytenoid cartilages and vocal
folds to abduct on inspiration. Congenital laryngeal paralysis has been reported in Bouvier de Flanders, Bull Terriers, Siberian
Huskies, Dalmatians, and Rottweilers. When seen in a young patient generalized neuromuscular disease should be suspected.
This disease is seen relatively commonly in dogs in referral surgery settings as the acquired, idiopathic form. The acquired
form of the disease occurs in geriatric 10-12 years of age) sporting and giant breeds such as Labradors, Golden Retrievers,
St. Bernards, and Afghan hounds. There is a sex predilection with males being affected more commonly. Although termed idiopathic,
many of these animals likely do have some form of neuromuscular disease, Hypothyroidism has been identified concurrently
with laryngeal paralysis. Hypothyroidism can cause a peripheral neuropathy with resulting weakness which responds to replacement
therapy; laryngeal paralysis however does not respond to replacement therapty. The disease is also seen occasionally in smaller
breeds and has been reported in a series of cats. Surgical procedures performed in the neck can also cause laryngeal paralysis
if the vagus/recurrent laryngeal nerves are injured. Thyroidectomy in cats has been a cause of laryngeal paralysis if care
is not taken to preserve the recurrent laryngeal nerves during surgery.
Clinical Signs
The most common signs are related to airway obstruction and include exercise intolerance, limb weakness, inspiratory dyspnea,
loss or change in bark, and respiratory stridor. Owners often report "noisy" breathing. Dogs with this disease may be presented
for heat related stress during the spring or summer months when they acutely decompensate due to impaired laryngeal function.
In cases of suspected laryngeal paralysis the cervical area should be carefully examined and palpated for the presence of
masses or foreign bodies. Physical examination if often unrewarding and definitive diagnosis is made by laryngoscopic or
endoscopic examination of the larynx and glottis. Thoracic and cervical radiographs should be taken to assess the thorax
for mediastinal masses and/or the presence of aspiration pneumonia and the cervical area for presence of extraluminal masses
and megaesophagus. The presence of megaesophagus is an ominous sign and is regarded as a contraindication to surgery by some
clinicians. We have identified "swallowing" abnormalities in some dogs. Dysphagia of any type should be pursued diagnostically
prior to any surgery for the laryngeal parlysis Neoplasia of the pharyngeal or laryngeal areas may also cause signs similar
to laryngeal paralysis. Hypothyroidism has been identified rather commonly in dogs with laryngeal paralysis and should be
tested for.
The definitive confirmation of a diagnosis of laryngeal paralysis is made by observing laryngeal function while the animal
is under very light anesthesia. It is essential that the animal retain the cough and gag reflex for laryngeal exam; if too
much barbiturate or other sedation is administered thereby abolishing the gag reflex an incorrect diagnosis of laryngeal paralysis
may be made. It is recommended that small doses of short acting barbiturates or propofol be administered to an animal without
premedication. Low doses of mixed ketamine and diazepam may also be used to aid in diagnosis of the disease. In dogs with
laryngeal paralysis, the arytenoid cartilages and vocal folds do not abduct on inspiration and the vocal folds are located
in a paramedian position. The examiner should strive to correlate any movement of the vocal folds with the phase of the respiratory
cycle. In dogs with paralysis, the vocal folds will often be moved slightly laterally by the passive expiration of air from
the lungs; this slight "flutter" movement should not be confused with abduction on the inspiratory phase. Laryngeal paralysis
in dogs is bilateral in most cases. If there is doubt about movement of the arytenoids or vocal folds dopram (1.0 mg/kg)
may be administered to stimulate respiration.
Data Base
We routinely obtain thoracic and cervical radiographs to look for aspiration pneumonia, mediatinal, and cervical masses,
Barium swallows are performed under fluoroscopy if the animal is dysphagic. Thyroid levels are routinely screened. Electromyography
may assist in some case but we do not routinely perform this test.
Ultrasonography of the larynx to diagnose laryngeal paralysis has been described. We do not have experience with this modality
as a diagnostic tool.
