Canine and feline laryngeal paralysis (Proceedings)
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.
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.
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.