Thyroid Gland Disorder in Dogs

The thyroid glands are located in the neck and produce hormones that help the body to function. In dogs, thyroid disease, also known as hypothyroidism, usually causes a deficiency of thyroid hormone production. Hypothyroidism is more common in medium to large breeds and middle-aged dogs (ages 4 to 10). Commonly affected breeds include Golden Retrievers, Doberman Pinchers, Irish Setters, Miniature Schnauzers, Dachshunds, Cocker Spaniels, and Airedale Terriers. It does not affect one sex more than the other. The majority of hypothyroidism cases in dogs are caused by the destruction of the thyroid gland.

Because of the role the thyroid plays in hormone production and assisting other hormone functions, symptoms may vary. Below are some symptoms your pet may exhibit:

• Slowed metabolism
• Lethargy
• Lack of desire to exercise
• Increased weight gain with no change in appetite
• Trouble staying warm
• Loss or thinning of fur
• Dull coat of hair
• Excess shedding
• Thickening of skin and increased skin pigment
• Ear infection, pain, redness and/or odor
• Skin infections
• Drooping of facial muscles
• Regurgitation (less common)
• Abnormal ability to walk (less common)

Hypothyroidism can also cause myxedema in dogs, which is the swelling of the skin and tissues below the skin, making the skin waxy. Myxedema is accompanied by some of the symptoms above, particularly weight gain and trouble staying warm. Myxedema very rarely leads to a myxedema coma, which can be fatal.

Types

Thyroid disorders are commonly classified into two separate types.

• Hypothyroidism - a decrease in the release of thyroid hormones, is the most prevalent in dogs. The decreased level of thyroid hormones slows the metabolic rate. A great majority of cases of hypothyroidism in dogs result from the destruction of the thyroid gland. A lesser cause is a tumor of the pituitary gland, which will exhibit deficiencies of the pituitary hormones.
• Hyperthyroidism - an increase in the release of thyroid hormones, is rare in dogs and much more common in cats. While hypothyroidism slows the metabolic rate, hyperthyroidism increases it. Symptoms of this type of thyroid disorder include weight loss, an increase in appetite, and increased heart rate.

Nearly all cases of hypothyroidism in dogs are caused by the destruction of the thyroid gland, which is caused by a genetic disorder. This genetic cause for hypothyroidism makes up 95% of all cases. Less likely, but possible, causes include: impaired thyroid hormone secretion, congenital abnormalities and other congenital defects.

There are a few options for diagnosing hypothyroidism in dogs:

• Physical exam
• Blood panel – while this may reveal symptoms of hypothyroidism, other illnesses can affect the results of this test
• Laboratory tests to monitor concentrations of thyroid hormones – your veterinarian may also try administering a thyroid-stimulating hormone to verify that the cause is hypothyroidism

Treatment of hypothyroidism aims to account for the deficiency in thyroid hormones. There are two types of medication, corresponding to the thyroid hormones: T3 and T4. Typically, the body will convert T4 to T3. Because of this, most dogs receive the T4 supplement. Only those unable to convert T4 will receive T3. This treatment must be given orally or in the ear for the rest of the dog’s life. In order to determine success, the treatment will be administered for 4 to 8 weeks. Serum thyroid hormone concentrations will be monitored until the dosage is stabilized.

The treatment for hypothyroidism is typically lifelong and is usually given by mouth or ear. The treatment will be administered from 4 to 8 weeks before effectiveness can be adequately measured. Regrowth of fur will also take 4 to 8 weeks. Until a stable dosage is found, multiple blood tests are required to measure the levels of thyroid hormone T4 in the blood and adjust the dosage. Once the dosage is stabilized, levels will be checked once or twice a year.

Your veterinarian will recommend running a few tests in order to diagnose hypothyroidism, specifically a physical exam and complete thyroid panel, which will cost $218 on average. Treatment will require supplements to replace the T3 and T4 thyroid hormones, which cost around $32 monthly. Cost may vary based on the pharmacy and veterinarian specifications.