Definition of Hypothroidism

Hypothyroidism is a clinical syndrome caused by inadequate production and release of the thyroid hormones triiodothyronine (T3) and thyroxine (T4), which are essential to normal metabolic function. The symptoms of hypothyroidism are varied and nonspecific. Hypothyroidism is not difficult to diagnose.

Causes of Canine Hypothyroidism

Primary hypothyroidism is the most common form of this disease and typically is caused by lymphocytic thyroiditis or idiopathic thyroid gland atrophy. These conditions involve immune-mediated destruction of or damage to the thyroid gland. For some reason, the affected dog’s immunologic defense mechanisms target its own thyroid tissues, as if they were foreign. Over time, circulating T3 and T4 levels diminish, causing a cascade of metabolic abnormalities. Environmental and dietary factors are possible contributors to hypothyroidism in dogs. Secondary hypothyroidism is rare in dogs. When it occurs, it usually is caused by congenital disease, pituitary gland disease, dietary iodine deficiency, space-occupying pituitary tumors or other abnormalities.

Preventing Hypothyroidism in Dogs

While hypothyroidism cannot realistically be prevented, it is not particularly difficult to diagnose or to treat.

Special Notes

Most dogs suffering from hypothyroidism can be well-managed on oral thyroid hormone replacement therapy. Dogs with hypothyroidism can be anesthesia risks, so additional precautions should be taken by the veterinary team prior to anesthetic induction. These dogs also tend to become very cold (hypothermic) when under general anesthesia. Because of the dog’s altered metabolism, anesthetic agents typically have a much more pronounced and unusually long-lasting effect.