Most of us know the larynx is commonly known as the “Voice Box” and it is located in the throat. We know that “laryngitis” is a condition where one cannot speak but other than that, the larynx does not get much thought. It is a vastly under appreciated organ. The larynx is not just where sound comes from; it is more importantly the cap of respiratory tubing. The larynx closes the respiratory tract off while we eat and drink so that we do not inhale our food. If we need to take a deep breath, the muscles of the larynx expand and open for us. The larynx is the guardian of the airways, keeping whatever we want to swallow out and directing air in.
Laryngeal paralysis results when the abductor muscles of the larynx cannot work properly. This means no expanding and opening of the larynx for a deep breath; the laryngeal folds simply flop weakly and flaccidly. In other words, when one needs a deep breath, one doesn’t get one. This can create tremendous anxiety (imagine attempting to take a deep breath and finding that you simply cannot). Anxiety leads to more rapid breathing and more distress. A respiratory crisis from the partial obstruction can emerge creating an emergency and even death.
Laryngeal paralysis does not come about suddenly. For most dogs there is a fairly long history of panting, easily tiring on walks, or loud breathing. Ideally, the diagnosis can be made before the condition progresses to an emergency.
IS LARYNGEAL PARALYSIS PART OF A BIGGER NEUROLOGIC PROBLEM
This question is still not fully answered. In one 1989 study, all dogs with laryngeal paralysis tested showed evidence of disease in long, large diameter nerve fibers in nerve biopsies from the rear legs. The suggestion was made that laryngeal paralysis represents “only the beginning” of a more widespread neurologic degeneration. If this were true, one would suspect we would see a more obvious disease progression but, in fact, it is not always clear that we do. At this time, acquired (non-congenital) laryngeal paralysis is largely an idiopathic (cause unknown) condition. We still can say that a dog with laryngeal paralysis is 21 times more likely to develop megaesophagus, another neuromuscular disease.
The suggestion has been made that hypothyroidism may be a cause of laryngeal paralysis. This question is also not fully answered. We know that other neuropathies associated with hypothyroidism will respond to treatment for hypothyroidism but laryngeal paralysis in a hypothyroid dog will not. It may be coincidental that many older large breed dogs are hypothyroid and also have laryngeal paralysis or it may be that the laryngeal paralysis represents a state of neurologic disease that is too advanced to respond simply to thyroid hormone supplementation.
MAKING THE DIAGNOSIS
In order to determine if a dog has laryngeal paralysis, the larynx must be examined and this requires sedation. The level of sedation must be heavy enough to allow the larynx to be visualized but light enough for the patient to be taking some deep breaths. If the sedation is too deep for the diagnosis to be obvious, a respiratory stimulant called Dopram® (doxapram hydrochloride) is given intravenously to stimulate several deep breaths so that the function of the larynx is clear. In a normal larynx, the arytenoids cartilages are seen to open and close widely. In a paralyzed larynx they just sit there limply while the patient breathes deeply.
If the patient is having a respiratory crisis when he or she sees the veterinarian, this diagnostic test can easily be followed by intubation (inserting a breathing tube down the patient’s throat). This relieves the upper airway obstruction and the patient can breathe normally, unfortunately, sedation must be maintained to keep the tube in place.
A newer technique of visualizing the larynx involves threading an endoscope down the patient’s nostril. This is tricky but the benefit is that sedation is not required. The downside is that specialized equipment is needed and the patient may not be cooperative.
There are some additional tests that are helpful in evaluating the patient with laryngeal paralysis. Chest radiographs are important in ruling out aspiration pneumonia (from inhaling food material through the non-functional larynx), megaesophagus (which we have mentioned tremendously complicates a laryngeal paralysis case), and obvious tumor spread. Radiographs of the throat to rule out obvious throat tumor are also helpful. Complete blood testing including thyroid tests should also be included in the work-up.
If laryngeal paralysis is not treated, a respiratory crisis can emerge. In this situation, the patient attempts to breathe deeply and simply cannot, creating a viscious cycle of anxiety and respiratory attempts. The laryngeal folds become swollen making the obstruction in the throat still worse. The patient’s gums become bluish in color from lack of oxygen and the patient begins to overheat. For reasons that remain unclear, fluid begins to flood the lungs and the patient begins to drown (as if the laryngeal obstruction wasn’t lethal enough).
The patient must be sedated, intubated and cooled down with water in order to survive. As soon as intubation is effected, the patient can breathe normally, oxygen can be administered and the crisis can be curtailed if it has not progressed too far.
But, of course, eventually the patient will have to wake up. Corticosteroids can be used to reduce the swelling but ideally one of several surgical solutions is needed.
The goal of surgery, whichever technique is used, is to relieve the airway obstruction permanently while maintaining the original function of the larynx (protection of the airways).
De-barking surgery is generally thought of as a surgical solution to a behavioral problem but it is also a fair treatment for laryngeal paralysis. The usual method involves extending a long “biting” forcep down the throat and biting out the vocal folds. Obviously anesthesia is needed to do this and the fact that the surgical area is the larynx makes normal intubation for anesthesia impossible. This means either using injectable anesthesia or placing a tracheostomy (cutting a hole in the throat lower down) and intubating through that.
Removal of the vocal folds, of course, also removes the patient’s voice reducing barking to a whisper. The hole created by the absence of the vocal folds makes for a larger airway opening and is generally large enough to relieve the obstruction. Complications of this surgery include swelling and bleeding (which can cause obstruction in themselves, though, if a tracheostomy is placed any such obstruction is bypassed), and regrowth of a webbing of vocal tissue. An alternative technique involves approaching the larynx from the outside of the throat instead of down the mouth. This method is more difficult and time consuming but has less chance of the development of webbing. A tracheostomy, if any, is allowed to heal closed.
Another surgical technique involves only biting out one vocal fold and also biting out the arytenoids cartilage on the same side. There is more bleeding with this technique and a tracheostomy becomes more desirable. Surgeries involving removing part of the larynx have been associated with a 30% mortality rate in laryngeal paralysis patients.
Laryngeal Tieback (also called Lateralization Surgery)
This has probably become the most commonly performed surgery for laryngeal paralysis currently. It involves placing a couple of sutures in such a way as to pull one of the arytenoid cartilages backward. By repositioning one of the arytenoids the opening of the larynx is changed (made larger). The chief complication of this procedure stems from the fact that only a few millimeters of position change in the arytenoids are needed. If the cartilage is moved too much, the larynx cannot properly close and aspiration pneumonia becomes a substantial risk. Commonly these patients have a persistent cough after eating or drinking. This surgery has been associated with a 14% postoperative mortality rate. (In older times, both arytenoids were tied back to create a still larger larynx but tying off both cartilages in this way was associated with a 67% mortality rate so it is no longer done).
In this surgery, a square of the thyroid cartilage is cut (similar to a castle’s turret’s square behind which an archer might hide). This square is moved forward and reattached to create a wider laryngeal opening. A tracheostomy is frequently needed to protect from swelling.
In June of 2001, the Journal of the American Veterinary Medical Association published a survey of complications in a group of 140 dogs receiving surgical treatment for laryngeal paralysis. Here is a summary of the results:
MacPhail CM, Monnet E: Outcome of and postoperative complications in dogs undergoing surgical treatment of laryngeal paralysis: 140 cases (1985-1998). JAVMA 218(12): 1949-1955, 2001.
While only about 10% of dogs being evaluated for surgical correction of laryngeal paralysis already have aspiration pneumonia, nearly 25% will develop aspiration pneumonia at some point. Pneumonia is always potentially life-threatening and aspiration pneumonia is particularly difficult to clear since it involves large contaminated food particles in the lung. Broad spectrum antibiotics, fluid therapy and physical therapy are important tools but, sadly, the underlying condition that led to the original aspiration pneumonia, is likely to produce future episodes. Please visit the library section on Pneumonia Management for details on treatment.
Page last updated: 3/9/2016