Hypothyroidism

Hypothyroidism is the most common endocrine (hormonal) disease in dogs. Breeds that are more commonly affected are the Golden Retriever, Doberman Pinscher, Boxer, Irish Setter, Airedale, Great Dane, Miniature Schnauzer, Old English Sheepdog, Shetland Sheepdog, Poodle and Dachshund. The disease is usually diagnosed in middle aged dogs, (2-9 years). It is very rarely diagnosed in cats.

The overall effect of thyroid hormone is to control the rate of metabolism. Symptoms of hypothyroidism tend to be vague and progress slowly. There are, however, changes in some parts of the body that can tip us off to a possible thyroid problem. Obesity that is resistant to weight loss despite appropriate diet, lethargy, exercise intolerance, weakness, and a tendency to seek out warm places are all common signs. Other signs include hair loss, dull or brittle haircoat, toenail loss, seborrhea, chronic skin and/or ear infections and increased pigmentation.

Diagnosis of hypothyroidism is made based clinical signs and blood tests. Blood tests that generally are performed include CBC, Chemistry, total T4 (TT4), free T4 (fT4), and thyroid stimulating hormone (TSH). All of these tests may be required to adequately diagnose the disease.

Once a dog is determined to be hypothyroid, a synthetic thyroid hormone supplement is prescribed. This is a medication they will take for the rest of their lives. It is important to monitor the dog’s hormone level once on thyroid supplementation. Giving a dog too much replacement hormone has detrimental effects and giving too little may not alleviate the symptoms. Initially, a thyroid test will need to be repeated until the right dose has been established. For some dogs this will require only a single test and others may require several. Thereafter, periodic retesting (generally every 6-12 months) is required to make certain the hormone supplement is adequate. Sometimes the need for supplementation will increase/decrease with age.

Improvement in the symptoms can be seen as early as 2 weeks (activity level) and take as long as several months. Haircoat changes frequently get worse before they get better (getting rid of the old, making room for the new).

Hypothyroidism is an important disease because it affects the overall quality of life of the dog. Often people do not realize the severity of the dog’s illness until they start supplementation and see the positive changes occur. Treatment for hypothyroidism is usually successful and dogs go on to live happier and more comfortable lives.