Most cases require the both sides to be dysfunctional before the signs are apparent enough to warrant attention.Īlso, because dogs require adequate breathing to cool off in warmer weather, we often see patients become more clinical during the spring/summer weather when it is warmer and more humid. Most cases of the paralysis on one side are not clinically apparent. The diagnosis of the dysfunction requires direct visualization of the larynx and determination that there is no abduction (move to the outside.) This generally requires some sedation and maybe the administration of medication to stimulate deep breathing. This may include radiographs (x-rays) of the neck and chest to identify possible tumors. It is important to rule out possible causes for the dysfunction of the nerve/muscle. Presenting signs include a change in barking, exercise intolerance, hyperventilation, raspy breathing, difficulty with warm and humid conditions, gagging (especially water), inability to breathe and collapse. Bouvier-des-Flanders dogs may be affected by a genetic disorder causing laryngeal paralysis and may be presented at much younger ages.
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Most of the patients presented with laryngeal paralysis are older – often greater than 10 years old. Nerve damage can be caused by hormonal imbalances (hypothyroidism) or trauma (neck or chest) or tumors in the chest or neck that involve the nerve. It has been suggested that there may be a degeneration of the nerve muscle complex in Labradors resulting in a progressive degeneration over the latter parts of their lives. Though any breed can be affected, we tend to see the condition in larger breeds including, but not limited to, Labradors, Golden Retrievers, hounds, etc.
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Laryngeal paralysis has been reported in a wide variety of animals. This can occur if the muscle is defective or the nerve to the muscle is defective. If the function of the CAD is compromised, the patient cannot maximally open the airway. The nerve that fires this muscle is the recurrent laryngeal nerve and this nerve travels from the chest (near the heart) and follows the trachea to the level of the larynx. During times of increased respiration, the body will hold the diamond open as much as possible by firing these muscles. The official name is the cricoarytenoideus dorsalis (CAD) muscle.
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The muscles that open the airway are located at the corners of the diamond – about at the 2 and 10 o’clock positions. The opening of the trachea is roughly diamond shaped. The lining of the box is mucosa – like the lining of the inside of the mouth. The voice box is made of a scaffolding of cartilage. Only one muscle on each side is designed to keep it open to allow maximal air flow in times of need. Most of the muscles in the larynx serve to close the opening to the airway down so that we do not choke. We know that laryngitis is a condition where one cannot speak and this is also true for dogs – the bark quality and resonance becomes affected. Most of us know the larynx is commonly known as the “voice box” and is located in the throat.