Hypothyroidism, or low thyroid function, is one of the most common canine hormone imbalances. This was not always the case. In recent decades, hypothyroidism diagnoses are on the rise.

What’s going on here?

In mammals, the endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream, that regulate the body. The thyroid gland, one of the largest endocrine glands, controls how quickly the body uses energy, makes proteins, regulates calcium and controls the body’s sensitivity to other hormones. The thyroid is critical to metabolic processes and affects the functionality of almost every other organ in the body. The endocrine system is highly sensitive, and its delicate dance of hormones can be disrupted, potentially resulting in disease. In dogs, the most common hormonal disorder diagnosed is hypothyroidism.

Typically, hypothyroidism occurs in dogs from 4-10 years of age, though in rare instances dogs can actually be born with it. Because the thyroid hormone affects the metabolism of the whole body, the clinical signs can be non-specific. That being said, dogs with hypothyroidism often exhibit low energy levels, weight gain, hair loss, a dull hair coat and concurrent skin infections.

Hypothyroidism can be mistaken for other endocrine disorders, and is best diagnosed by a complete thyroid panel blood test. The tricky thing about the thyroid gland is that the level of hormone release can be influenced by other physical factors, making true hypothyroidism difficult to diagnose. For example, stress caused by other illnesses can reduce thyroid function. Often, when these issues are addressed, thyroid levels normalize without additional treatment. Studies have shown that dogs treated with topical steroids or phenobarbital (to control seizures) can artificially lower thyroid hormone. If your dog takes a long-term medication with thyroid-related side effects, treatment may be necessary to minimize the impact.

The most frustrating thing about canine hypothyroidism is that its cause remains unknown. What is known is that almost 80% of all canine hypothyroidism cases are caused by an autoimmune inflammatory disorder, called lymphocytic thyroiditis (source: Antech). Other hypothyroidism cases are linked to ‘idiopathic atrophy’, which is a fancy way of saying ‘the thyroid tissue disappeared and we don’t know why’, which many veterinarians believe is just end-stage autoimmune thyroiditis. Furthermore, tumors and rare birth defects can also cause the disease.

But don’t freak out because it’s not all bad news! Since the bulk of canine hypothyroid cases is due to a condition similar to Hashimoto’s and Grave’s disease in humans, a huge amount of research is ongoing to determine the causes, treatment and prevention of thyroid disorders. Autoimmune thyroiditis is currently thought to be a genetic disease, exacerbated by external factors, such as diet or viral infections. In humans, current research is finding links between celiac disease (gluten sensitivity) with inflammatory thyroid conditions.

References:

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Stazi AV, Trinti B. Selenium status and over-expression of interleukin-15 in celiac disease and autoimmune thyroid diseases. Ann Ist. 2010;46(4):389-99.

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Choi EW, Shin IS, Bhang DH, Lee DH, Bae BK, Kang MS, Kim DY, Hwang CY, Lee CW, Youn HY. Hormonal change and cytokine mRNA expression in peripheral blood mononuclear cells during the development of canine autoimmune thyroiditis. Clin Exp Immunol. 2006 Oct;146(1):101-8.

Makino M, Oda N, Miura N, Imamura S, Yamamoto K, Kato T, Fujiwara K, Sawai Y, Iwase K, Nagasaka A, Itoh M. Effect of eicosapentaenoic acid ethyl ester on hypothyroid function. J Endocrinol. 2001 Nov;171(2):259-65.

Graham PA, Refsal KR, Nachreiner RF.Etiopathologic findings of canine hypothyroidism. Vet Clin North Am Small Anim Pract. 2007 Jul;37(4):617-31