The larynx (sometimes
called the voice box) is a muscular and cartilaginous structure that connects
the pharynx (throat) and trachea (windpipe). The larynx contains the vocal
cords. These are the muscular structures within the airway that vibrate when air
passes by them allowing us to talk, bark, or meow. The opening to the larynx is
covered by the epiglottis, a large muscular flap that covers the windpipe when
we swallow to prevent food from entering the trachea. The larynx also closes to
prevent aspiration of food and water. This function of the larynx is so
important that, of the eight muscles of the larynx, seven of them are
responsible for closure. The remaining muscle (cricoarytenoideus dorsalis)
functions to open the laryngeal portion of the airway by abducting (pulling
open) the arytenoid cartilages when we inspire. If the muscle stops functioning
properly, the airway cannot remain open as we breathe, causing gasping episodes
which may become life threatening (see Fig. 1 and 2).
Laryngeal paralysis is a
failure of the laryngeal cartilages to open during inspiration, creating a
partial or complete upper airway obstruction (see Fig. 2). It is usually caused
by dysfunction of the nerve (recurrent laryngeal nerve) that controls the
laryngeal musculature. This can be secondary to a disease process that affects
all of the nerves of the body (polyneuropathy) or secondary to a traumatic event
that affects only the laryngeal innervation. Generalized neuromuscular or
muscular disease can also result in laryngeal paralysis. Most of these
processes, with the exception of a traumatic episode, are slowly progressive
until an acute exacerbation causes a life threatening crisis. In a life
threatening crisis, an emergency tracheotomy may be necessary to bypass the
compromised airway until definitive surgical correction can be performed.
The clinical signs of
laryngeal paralysis most commonly begin as a vague change in the quality of the
voice and then progress to noisy breathing (sometimes called "roaring"),
inspiratory dyspnea (difficulty breathing), and stridor (noisy gagging or
coughing). Cyanosis (a blue tinge to the tongue due to lack of oxygen) may also
be present. A lack of oxygen is life threatening. The signs of laryngeal
paralysis are often made worse by exercise, hot and humid weather, or obesity.
Aspiration pneumonia can occur during violent gasping and gagging episodes.
Diagnosis and Treatment
The diagnosis of laryngeal
paralysis involves direct observation of arytenoid function during respiration.
This is usually performed under heavy sedation or light anesthesia. During
normal breathing, the larynx is abducted (pulled open). This allows air to flow
down the trachea and into the lungs. Dogs with compromised airflow through the
larynx must work harder to fill their lungs with air. This decreases airway
pressure and pulls the laryngeal walls into the airway. The laryngeal walls
close in front of the opening to the trachea and block the flow of air.
Emergency procedures such
as sedation, oxygen, corticosteroids, or tracheotomy may be required for
stabilization but surgery is the only permanent correction for laryngeal
paralysis. An arytenoid lateralization is a procedure that uses sutures to hold
the laryngeal portion of the airway open. This can be performed either
unilaterally (one side) (see Fig. 3) or bilaterally (both sides). The suture is
passed through the arytenoid cartilage to the outside of the larynx and tied.
This abducts (pulls out) the arytenoid cartilage and prevents arytenoid
hospitalization for 24 to 72 hours is required due to the potential for
aspiration and laryngeal swelling. Broad spectrum antibiotics and
antiinflammatory medications are administered for five to ten days.
Occasionally, sedatives may be required. It is also important that the dog not
be allowed heavy exercise during hot or humid weather and that excessive weight
gain is avoided.