To understand laryngeal paralysis, it is important to first understand some basic anatomy and function of the larynx. The larynx is commonly referred to as the "voice box", and is located in the throat. Not only is the larynx where sound comes from, but it also acts as a cap to the airway. The larynx closes the respiratory tract off when when we swallow (while eating or drinking) so that food is not inhaled. The larynx expands and opens when we are breathing, and can be opened extra wide if we need to take a deep breath.
Laryngeal paralysis happens when there is malfunction of certain nerves that control the muscles of the larynx. This means that the larynx can no longer expand and open up to allow deep breathing, and the laryngeal folds hang weakly in the back of the throat resulting in a smaller opening to breath through. Laryngeal paralysis can be unilateral (affecting only 1 side of the larynx) or bilateral (affecting both sides). To understand how a dog with laryngeal paralysis feels, imagine if you were forced to breath through a straw. This may be fine as long as you were relaxed and at rest, but imagine how things would change if you were running around the block and needed more oxygen than you could get through your straw. If you needed big deep breaths and were unable to take them, you would probably feel a great deal of anxiety. Anxiety leads to more rapid breathing and distress - a vicious cycle. The other problem with laryngeal paralysis is incomplete protection of the airway when swallowing, allowing inhalation of food/liquids. Animals affected with laryngeal paralysis have a reduced tolerance for stress, exercise, and heat, and in severe cases this may lead to a fatal respiratory crisis.
In the majority of cases the cause of laryngeal paralysis is unknown, though it can sometimes occur secondary to hypothyroidism, neuromuscular diseases, cancer, or trauma. While it can occur in any dog, it is most commonly seen in middle aged to older large and giant breed dogs. There is also a hereditary form of laryngeal paralysis which occurs in certain breeds that will show up before 1 year of age.
Symptoms of laryngeal paralysis include a change in voice, gagging and coughing especially after eating or drinking, noisy breathing, excessive panting, heat and exercise intolerance, and in severe cases cyanosis (blue tinged tongue and gums which indicates inadequate oxygen levels in the blood), and syncope (fainting). Laryngeal paralysis can also result in aspiration pneumonia or an acute respiratory crisis, both of which can be fatal.
To diagnose laryngeal paralysis, it is necessary to directly visualize the laryngeal folds as an animal breathes. This is usually done by lightly sedating the pet and then looking down the back of the throat with a laryngoscope. In a normal larynx, the arytenoid cartilages are seen to open and close widely as the animal breathes. In a paralyzed larynx, one or both of these cartilages just hang limply in the back of the throat. A newer technique to visualize the larynx involves passing an endoscope down the nostril, though this does require specialized equipment. Additional testing may include radiographs to rule out aspiration pneumonia, megaesophagus (which complicates a laryngeal paralysis case), and cancer. Complete blood work including thyroid levels is also recommended.
Many dogs with mild laryngeal paralysis respond well to environmental and medical management. Affected dogs should be kept relatively calm and should have limited exercise. It is best to avoid the summer heat and to switch to a harness rather than a collar to reduce any pressure on the neck. Weight loss can be very beneficial as symptoms are more severe in obese pets. Medications that may be used include mild sedatives, corticosteroids to reduce swelling and inflammation in the throat, and bronchodilators to open up the airways.
Many dogs with this condition may have a sudden respiratory crisis often associated with heat, stress, or exercise. In this situation, the laryngeal folds become swollen making the obstruction of the throat worse and creating a vicious cycle of anxiety and respiratory attempts. These dogs must be sedated, stabilized with oxygen therapy and medications, cooled down with water, and sometimes require intubation or a tracheotomy.
Aspiration pneumonia is another common complication associated with laryngeal paralysis. Pneumonia is always potentially life threatening, and aspiration pneumonia is especially difficult to cure due to the large contaminated food particles in the lungs. Antibiotics, fluid therapy, and physical therapy may all be included in the treatment of this condition.