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Laryngeal paralysis is a common disease of the aging large breed dog (Labrador
Retrievers, Great Danes, etc) that starts, initially, as only a change in your
pet's voice character. As the disease progresses, there can be significant
interference with your pet's ability to take in sufficient air into their lungs.
Breathing becomes much more "noisy" and, in some instances, is quite loud.
Laryngeal Paralysis (LP) is caused by a paralysis of one or both sides of the
opening into the pet's larynx. This paralysis is generally caused from a loss
of normal nerve function to that side or sides of the larynx. As the nerve gets
sicker, normal breathing movements of the larynx, during inspiration, are more
restricted with very little motion noted. Eventually, the openings into the
larynx and trachea become so narrowed, it's like your pet is "breathing through
a straw." These patients suffer from severe hypoxia and simply cannot get their
breath.
No one really has determined the ultimate reason for the degeneration of this
nerve, but several theories have arisen over the years. The primary nerve
affected is the recurrent laryngeal nerve. In the horse, LP is fairly common
and can destroy, of course, a race horse's career. It is well known in all
species that the recurrent laryngeal nerve is likely the longest nerve in the
body. In large breeds of dogs and "long-necked" horses, these nerves are
sometimes several feet in length. One of the theories is the postulate that
these nerves are constantly being stretched (overstretched?) and that this is
detrimental to the health of the nerve. Poor thyroid function has also been
posited as a reason; this makes a lot of sense, especially in many of the
breeds predisposed to hypothyroidism (Labrador Retriever).
Treatments have included a number of medications in an attempt to reduce edema
and airway swelling because of airflow changes, but, consistently, the most
important treatment is a surgical correction of the "adducted" or paralyzed
portion of the larynx. The portion of the larynx that appears paralyzed is the
arytenoid cartilage and lateral ventricles or vocal folds. One of the procedures
involves removal of the arytenoid cartilage and lateral ventricle. A second
procedure involves only removal of the lateral ventricles. Finally, the most
successful operation is that of lateralization of the arytenoid cartilages,
also known as a "tie-back" procedure.
The video accompanying this article is taken from our patient caseload and
represents a dynamic look at the arytenoids during inspiration. In a normal
patient, the two sides of the opening would be pulled away or abducted from
the middle at each inspiration.
In the video, our patient shows that neither side is very active, but the right
side almost has no movement whatsoever. This, then, is indicative of laryngeal
paralysis. This particular patient was very subdued most of the time, simply
due to oxygen deprivation. He was anxious and did not sleep well. When excited,
he would become very unsteady on his feet and actually collapsed on numerous
occasions.
Be watchful in your older "big dogs" for any changes in voice character or
breathing. Laryngeal paresis - paralysis is not an uncommon finding.
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