What are the causes of laryngeal paralysis?

The signs associated with laryngeal paralysis are usually caused by a dysfunction of one or both recurrent laryngeal nerves. These nerves supply the muscles that are responsible for holding the vocal cords open during inspiration (breathing in) and therefore failure to work effectively can result in partial obstruction of the upper airway. Often, these nerves are not the only ones affected and therefore incoordination or failure of function of nerves supplying other parts of the larynx (voice box) can contribute to food or water gaining access to the airway during swallowing and altered phonation (barking/mewing).

The more common causes of laryngeal paralysis include:

• Peripheral polyneuropathy (generalized nerve dysfunction). In this condition, the recurrent laryngeal nerves are dysfunctional or non-functional due to a pathology that affects many of the nerves in the body. The reason the condition often reveals itself first in the larynx may be that the recurrent laryngeal nerves are among the longest in the body and they are therefore very susceptible to diseases that reduce their ability to conduct impulses. In addition, these nerves are among the few in our pets where a failure of very fine control is easily noticed. A neurological examination carried out by a veterinary surgeon can reveal subtle signs of nerve dysfunction elsewhere in the body. The exact cause of the nerve dysfunction is often unknown.
• Trauma – trauma to the recurrent laryngeal nerves can lead to poor or absent function.
• Iatrogenic – this is the term used to describe a condition resulting as a complication or result of medical treatment. Surgery of the neck in dogs and cats (e.g. thyroid gland removal) can result in unavoidable damage to the nerves supplying the larynx.
• Tumors affecting the neck or front part of the chest cavity can place pressure on the nerves and cause them to malfunction.
• Hormonal disturbances – poorly controlled hypothyroidism (under-active thyroid gland) can cause peripheral neuropathy and has been proposed as a possible cause of laryngeal nerve dysfunction.