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
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 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.
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