Canine laryngeal paralysis and hypothyroidism are two conditions that can be sometimes found together. In order to better understand why hypothyroidism has been identified quite commonly in dogs with laryngeal paralysis, it helps learning more about how low thyroid levels affect the dog's body and in particular, the dog's larynx. Based on the fact that the two conditions can be sometimes found together, dogs suspected of having laryngeal paralysis should have their thyroid levels tested. Following is some information about canine laryngeal paralysis and hypothyroidism.
Low Thyroid Levels in Dogs
Hypothyroidism, a condition known for causing low levels of thyroid hormones, is one of the most common endocrine disorders affecting middle-aged and older dogs. It tends to occur when the dog's thyroid gland stops producing sufficient quantities of a hormone known as thyroxine or T4.
This hormone is responsible for controlling a dog's metabolic rate, and therefore, the more T4, the faster the metabolism, the less T4, the slower.
In dogs who are hypothyroid, lowers levels of T4 therefore lead to a sluggish metabolism. Affected dogs will tend to sleep a lot, become lethargic, put on weight despite not having much appetite, and seek warm areas. On top of this, affected dogs develop dull coats, become prone to infections and develop a typical symmetrical hair loss on the trunk and tail (rat tail).
On top of these common symptoms, low thyroid levels have also been known to impact the dog's nervous system and muscles. Although it's not very common, in some cases, dogs with low thyroid levels may manifest exclusively with neurological signs as the only clinical signs.
Laryngeal paralysis, on the other hand, as the name suggests, is the paralysis of the dog's larynx, also known as "voice box." When the nerves supplying the dog's laryngeal muscles, become weakened (paretic) or paralyzed, the muscles relax and the arytenoid cartilages forming the dog's larynx tend to collapse inwards, causing a restriction to a dog's ability to breathe deeply.
Since low thyroid levels are known to impact a dog's nervous system and muscles, it would be interesting therefore determining whether there is some sort of connection between canine laryngeal paralysis and hypothyroidism. A good way to better understand whether there is, is by looking at some studies.
What Studies Say
It is pretty clear that low thyroid levels are often present in dogs with laryngeal paralysis. A 2017 case report from Ankara University, Faculty of Veterinary Medicine in Ankara, Turkey reveals a case of a 12 year-old, female Golden Retriever with hypothyroidism-induced acquired bilateral laryngeal paralysis.
This case report is though very unusual, for the fact that this dog presented without any other systemic and dermatological signs commonly seen in dogs with primary hypothyroidism.
Laryngeal dysfunction has been reported in dogs with low thyroid levels in some other studies. In a study including 140 dogs suffering from laryngeal paralysis, 30 were found to have hypothyroidism, however, while the treatment of choice for low thyroid levels is the use of thyroid supplementation, unfortunately use of such medication does not appear to do much to resolve the laryngeal dysfunction.
While it is clear that low thyroid levels are often present in dogs with laryngeal paralysis, what remains unclear is whether there is a correlation between hypothyroidism and laryngeal paralysis. There are chances that the onset of both conditions are in most cases unrelated and that simply older dogs go on to develop both conditions as a part of the aging process.
Dr. Jean Dodds, feels though that there may be chances that there may be a correlation, only that it's not recognized. Perhaps, concomitant surgical interventions to correct the larynx may mask the effectiveness of thyroid medications in reversing further nerve damage, or perhaps, when low thyroid levels are diagnosed, it is now known how much thyroid medication is needed to prevent further deterioration of the nerves.
Certainly, this is something that warrants further research. Until then, it is important to have dogs with laryngeal paralysis tested for hypothyroidism through a T4 blood test, and if possible TSH level, or TSH stimulation test.
A More Generalized Neurological Disorder
Often, it turns out that laryngeal paralysis is just one symptom of GOLPP, an acronym that stands for geriatric onset laryngeal paralysis polyneuropathy.
It was Bryden J. Stanley, a board-certified veterinary surgeon, who started researching laryngeal paralysis in 2005, to reveal that laryngeal paralysis is the first sign of a slow-developing, generalized neurological disorder.
Stanley's study revealed that 75 percent of dogs diagnosed with laryngeal paralysis also exhibited signs of esophageal dysfunction, and that, at the time of diagnosis, 31 percent showed neurological abnormalities, particularly affecting the hind legs.
After one year, all dogs showed signs of other neurological issues such as the inability to walk and muscle wasting affecting the muscles of the back legs, muscles of the spine and muscles on top of the head.
Unfortunately, there is currently no therapy that has been proven effective in reversing the nerve degeneration associated with GOLPP. Without surgery to fix the laryngeal dysfunction, dogs may develop respiratory collapse and even sudden death from suffocation.
Unfortunately, the surgery to fix the laryngeal dysfunction, commonly known as "tieback surgery" has risks for complications and it will not have any positive effects on the progressive nerve degeneration affecting the dog's hind legs.
- Panciera DL, 1994: Hypothyroidism in dogs: 66 cases (1987-1992). JAVMA, 204(5), 761-767
- Michigan State University, College of Veterinary Medicine, GOLLP
- DVM360: Laryngeal paralysis in dogs and cats (Proceedings)