Laryngeal Paralysis

The larynx, or voice box (Adam’s apple) is a complex organ with several functions. Two of its main function are voice production and regulating air flow into the trachea (windpipe) and lungs. Many muscles are involved in laryngeal control, but only a single, paired muscle on either side is responsible for opening the larynx to widen the diameter of the airway, and thus permit more air to flow into the lungs with less resistance. Loss of this muscle function on one side is termed hemiparesis (weakness) or hemiplegia (complete paralysis). In horses (mostly Thoroughbreds) this unilateral condition typically occurs on the left side, and causes affected animals to breathe more noisily. These horses are called “roarers”, and their athletic performance can be affected. In dogs, we do not know the incidence of hemiparesis or hemiplegia, since most dogs don’t race or jump hurdles to an extent that we would recognize the signs. When dogs are seen for laryngeal problems it is almost always due to bilateral laryngeal paresis or paralysis.

Early on, dogs affected by laryngeal paresis tend to have signs such as voice change (weaker or hoarser bark), and stridor (a raspy-sounding respiration). They otherwise may act and function normally. However, as the disease progresses to complete paralysis, these signs become more severe, and dogs begin to exhibit poorer tolerance for sustained activity, may have trouble with exertion such as stair climbing, and may become very distressed with warm weather. Some dogs, if untreated, will develop more life-threatening signs of respiratory distress. They will heave with great effort to inspire (breathe in), may collapse, and their gums and tongue turn blue (cyanosis) due to inability to get enough oxygen into their lungs. If not treated promptly dogs with severe laryngeal paralysis will die from suffocation and hyperthermia (over-heating).

There is no effective medical treatment for laryngeal paralysis. The key to successful treatment is to provide a larger opening in the larynx for air to pass through with lower resistance. Currently there are no proven surgical treatments for restoring normal function to the affected paralyzed muscles. The treatment, therefore, is to create a permanently larger diameter opening. Older treatments accomplished this via partial laryngectomy, the actual removal of a portion of the larynx from one or both sides. These operations are rarely performed anymore because of high morbidity and complication rates.

The preferred surgical method of treatment is termed arytenoid lateralization laryngoplasty. In simpler terms, the cartilage and tissues that used to be pulled back by the now paralyzed muscles are “tied back” into a fixed, but more open position with specially placed sutures. These tie-back procedures are usually very successful in restoring dogs to a more normal quality of life, and preventing respiratory distress.

Common Questions, Concerns, and Complications Associated With Laryngeal “Tie-Back” Surgery:

1. What causes laryngeal paralysis? In most cases the cause is unknown (idiopathic). There appears to be a genetic predisposition since certain breeds are seen with this problem more frequently than others. But it can be seen in any breed of dog and sometimes in cats, too. Some dogs with laryngeal paralysis have hypothyroidism, but this appears to be more of an association than a cause. In some patients laryngeal paralysis may be part of a larger syndrome of neuromuscular disease, and other tests and treatments may be needed in addition to the "tie back."
   
2. My dog is older. Does it make sense and would it be safe to do such surgery? Laryngeal paralysis rarely develops in younger patients. Most affected dogs don’t develop the earliest signs until 10 years of age or older, and most dogs that reach the point of requiring surgery are in their early to mid-teens. Despite this, the success rate is still very high and most of these dogs go on to lead very good quality lives for a substantial period of time after laryngeal surgery.
   
3. What can I expect after surgery? Most dogs will be immediately quieter in their breathing and exhibit little effort to inspire compared with their pre-operative status. Many dogs will go home the day after surgery, and some may need tranquilizers to keep them from barking (barking places obvious stresses on the surgery site, so we try to minimize this until healing is complete). Because the airway is permanently tied open, the vocal cords will not resonate normally. So most dogs will continue to have the quieter, hoarser voice that they had before surgery when they bark. Dogs may also be prone to some coughing and gagging after surgery, especially when they eat and drink. Part of normal laryngeal function is to close the opening when swallowing food and water. After tie-back surgery laryngeal closing is somewhat compromised and we rely more on the epiglottis to protect the airway as food or water passes through the pharynx on its way to the esophagus (This crisscrossing of the breathing circuit and swallowing circuit in the pharynx was not one of evolution’s better adaptations!).
   
4. What can my dog eat after laryngeal surgery? Because of the somewhat increased risk for aspiration (food or water “going down the wrong pipe”) we usually recommend moistened food, dividing daily intake into several smaller meals. Over time, many dogs are able to resume eating normally.
   
5. What activity restrictions will my dog need? In the immediate period after surgery dogs should be kept quiet and taken for short leash walks. A harness for attachment of the leash is preferred to tugging on a collar around the neck, for obvious reasons. As they recover, dogs can resume normal levels of activity. The only major limitation is that dogs should no longer be allowed to swim after they have had tie-back surgery. When dogs swim they tend to skim along the surface and keep their mouths open. With the higher risk for aspiration (as above), this places a swimming dog at much higher risk for getting contaminated water into the lungs, and inducing a pneumonia.
   
6. Other than swimming, are there other risks for pneumonia? Because of the permanently widened airway and loss of ability to close the opening when swallowing, dogs with tie-back surgery are inherently at higher risk for aspiration-induced pneumonia. Fortunately, this is an uncommon complication, but does occur on occasion. Dogs that have more generalized neuromuscular problems (especially if swallowing is affected, too, and there is regurgitation occurring or excessive saliva in the pharynx) are at greater risk for complications. One way we try to prevent such complications as pneumonia is to not over correct the airway diameter. We know from physics that resistance to flow through a tube is related to the fourth power of the radius of the tube. In simpler terms, a small increase in the size of the opening results in a dramatic reduction in the resistance. For this reason, even though dogs with laryngeal paralysis are affected bilaterally, we usually only operate to tie back one side. And then we try not to tie that one side back excessively.