Hypothyroidism in dogs

Written by Kate Abbott Reviewed by Kristin Westafer, DVM

Overview

Hypothyroidism occurs when the thyroid does not produce enough thyroid hormones for normal body functions. Destruction of the thyroid glands causes the majority of hypothyroidism cases in dogs (about 95%). About half of the cases of thyroid gland destruction are caused by the dog's own immune system mistakenly attacking and damaging healthy thyroid cells – autoimmune thyroiditis. The other half is caused by atrophy (wasting) of the thyroid tissue. Normal aging can be one cause of atrophy but sometimes the cause for this form of the disease is unknown, idiopathically reduced thyroid function. (Idiopathic is a medical term which means from an unknown cause.)

Hypothyroidism is the most common hormone imbalance of dogs but is rare in toy and miniature breeds of dogs. Males and females are equally affected, although spayed females appear to be at a higher risk than intact females. This disease is often overly and mistakingly diagnosed because of the confusion surrounding the diagnostic tests.

Breeds that may be predisposed to developing hypothyroidism include:

Symptoms

The thyroid is primarily known for its role in regulating metabolism, but also affects many organs in the body, showing many different symptoms.

Weight gain
Dull, thin coat and hair loss (especially along the lower back, tail, back of the rear legs, and along the abdomen)
Dry skin
Persistent ear infections
Drooping of the skin of the face
Thickening and/or discoloration of skin tissues, especially of the face and head
Lack of energy, lethargic
Tiring quickly from exercise
Intolerance to cold

Treatment

Hypothyroidism is easily treated by daily doses of an oral synthetic thyroid hormone called thyroxine (levothyroxine). Your veterinarian will determine the dose and frequency depending on the severity of the disease and the response of the dog. Periodic blood tests are needed to keep the dose adjusted appropriately. Hypothyroid dogs who receive proper treatment have a normal life span and are able to maintain good health for many years.