Laryngeal paralysis causes respiratory (breathing) noise and exercise intolerance in medium and large breeds of dogs. The disease is very slowly progressive and may start very subtly, so by the time you notice significant breathing noise or inability to exercise it might be quite far progressed. If you notice these changes in your dog you should seek veterinary advice and have a vet check your dog for possible associated problems or diseases.
The larynx is the voicebox, but it has many other functions than producing sound. All of the functions of the larynx require the vocal cords to open and close. Tensing of the vocal cords during air movement produces sounds. When your dog breathes in, the vocal cords open to allow more air in, the harder the breathing, the more open the larynx is to maximize air flow.
The larynx also stops food and liquids from entering the windpipe (trachea). During swallowing or vomiting, the vocal cords move together to completely close the opening of the larynx. If any food, water, or irritant reaches the larynx, trachea, or lungs, coughing occurs to force foreign materials out of the larynx or airways.
Just before coughing, a deep breath is taken to completely fill the lungs, and the larynx opens wide to let that large amount of air in. During the cough, the larynx closes partially, making the air move rapidly at a high pressure, pushing out the abnormal material.
Laryngeal paralysis is lack of function of the larynx due to damage or degeneration of the nerve supply to the laryngeal muscles. Loss of the nerve function leads to loss of muscle contraction. The end result is a larynx that cannot open and close normally.
If the vocal cords cannot move out of the larynx, the larynx does not open wide enough to allow maximum airflow. If this happens your dog will not be able to exercise normally and can even progress to episodes of collapse, or passing out.
Laryngeal paralysis is typically a disease of larger breed dogs (such as setters and Labrador retrievers) and some medium breeds (Brittany spaniel). In most cases the nerves degenerate over time as part of a general disease of the nerves. Because the nerves degenerate slowly the signs of disease are not seen until dogs are quite old, usually more than 9 years old.
However some dogs have other diseases that cause laryngeal paralysis and may be affected at less than 1 year of age. In most affected dogs the signs really only affect the larynx but some dogs may have diseases affecting other nerves in the body and these may show signs of regurgitation (inability to swallow food properly) or difficulty in walking.
The first sign of laryngeal paralysis may be a subtle change in bark. Slowly progressing, the condition then results in noisy breathing, especially during panting. The noise is usually much worse during activity, when maximal air flow is required. Since the vocal cords cannot move, they sit in the airway and vibrate as the air flows by, resulting in the noise that we call “stridor.”
If the condition progresses, your dog may not be able to move sufficient air through the larynx panting (in hot weather) or during exercise, resulting in a blue tinge to the tongue and lips. In hot weather your dog may be at risk of developing heat stroke as efficient panting is the dog’s main cooling mechanism. The worst clinical signs are those of collapse, passing out, and potentially death.
Your vet will listen to your dog’s breathing and can recognise the stridor, or noise, as being more prominent during inhalation, or when you dog breathes in. They will also carefully listen to the lungs in an attempt to diagnose aspiration pneumonia. Other conditions can also cause coughing and exercise intolerance, such as heart disease, so listening to the chest with a stethoscope is very important.
An ultrasound machine can be used to look at the vocal cords during breathing but the best way to diagnose laryngeal paralysis is to look directly at the larynx. In order for your vet to do this your dog will need to have a very mild general anaesthetic so that your dog will allow the vet to look into your dog’s throat.
Although it is uncommon to find an underlying cause for laryngeal paralysis your dog should be tested for the conditions that can cause laryngeal paralysis. If one is missed, the condition could lead to more signs in the rest of the body, such as the regurgitation or difficulty walking. Since the larynx cannot close to protect against aspiration pneumonia, chest X rays are important. They also allow the heart size and shape to be evaluated for potential heart disease that could cause coughing and exercise intolerance.
Your dog’s general health should be assessed prior to general anaesthesia required for laryngeal examination, so blood and urine samples are usually tested. If your vet has any concerns about other specific diseases they may want to perform other tests.
Once nerve and muscle function are lost they cannot be recovered. If the laryngeal paralysis results in a decreased quality of life, a surgery can be done to permanently tack one side of the larynx in an open position and allow better airflow past the vocal cords. A vet with experience with this type of procedure should be able to perform the surgery with minimal difficulty. Your vet may want to refer your dog to a specialist surgeon for the operation.
Laryngeal paralysis is a slow, progressive disease. You may not notice early changes, as you are with your dog every day and mild changes are hard to recognise. Changing your dog’s activity level and keeping them in a cool environment may help and your dog may be more comfortable wearing a harness rather than a collar.
If the condition is affecting your dog’s quality of life, you can consider surgery. Surgery may never be done or can be done early in the course of the disease. The most important thing is to know what you and your dog like to do for a happy quality of life and to know the potential outcomes after surgery.
For an experienced vet the surgery is rapid and relatively straightforward. After surgery you must keep your dog quiet for a couple of weeks to ensure that healing has occurred. If the stitches break during this period then the vocal cords will flop back into the larynx.
After surgery one vocal cord is always in an open position, so the ability to protect the airways and lungs is permanently lost. Your dog may cough or clear its throat more frequently, especially when eating, drinking, or exercising because material may contact the larynx and first part of the trachea.
Your dog will always be at risk of developing aspiration pneumonia after surgery. Some dogs never get it, some get it once and respond to treatment, some get it repeatedly, and rarely a dog dies of aspiration pneumonia. Early detection and treatment are key to minimising the affect of aspiration pneumonia.