Hypothyroidism is a common endocrine disorder often seen in middle to older aged dogs, as a result of a decrease in the thyroid hormones produced by the thyroid gland. An underactive thyroid can have negative consequences on the body’s metabolism.
The thyroid gland is located in the lower neck. It is divided into two parts called lobes which are positioned either side of the windpipe (trachea). It is here where thyroid hormones important for metabolism, mainly thyroxine (T4) and to a lesser extent triiodothyronine (T3), are produced.
The thyroid hormones influence the function of almost all organs within your dog’s body. They are essential for normal growth and development, and regulate your dog’s metabolism. As such, the symptoms of hypothyroidism are very diverse.
Hypothyroid dogs may become apathetic, weak, sleep more frequently or for longer periods of time, inclined to suffer chills or gain weight without changes to their diet.
The most common cause for hypothyroidism (directly affecting the thyroid gland) is an immune system disease causing the body’s immune system to overreact.
The thyroid gland becomes inflamed as a result of the action of antibodies directed against the body’s own tissues, resulting in a decrease in thyroid hormone being produced by the thyroid gland. This stage is referred to as an autoimmune-mediated lymphocytic thyroiditis.
Other causes of hypothyroidism, such as tumours of the thyroid gland, radiation and congenital thyroid disorders are very rare.
Occasionally, a tumour of the pituitary gland can also cause hypothyroidism. This is referred to as secondary hypothyroidism.