Hypothyroidism, an under production of thyroid hormone, is reported to be the most common hormonal disease in dogs. It may affect any breed as well as mixed breed dogs. Golden Retrievers, Doberman Pinschers, and Labrador Retrievers appear to be at an increased risk of developing the disease. Typically, one sees hypothyroidism in dogs between the ages of 6 and 10 years, but it can appear at 2 years of age in large and giant breeds and those previously mentioned at-risk breeds.
Signs of Hypothyroidism
Skin changes associated with the disorder include:
- Hair loss involving bridge of nose, trunk, tail and elbows
- Dull, dry, brittle coat with poor hair regrowth when clipped
- Blackening of the skin
- Thick, puffy skin (called myxedema) that is cool to the touch
- Recurrent skin infections.
Systemic signs of the disease may include:
- Cold intolerance
- Gastrointestinal problems
- Muscle weakness
- Heart problems
- Neurologic problems.
It is important to note that the presentation of hypothyroidism in dogs is variable and many patients may exhibit only a few of the above mentioned clinical signs.
How is Hypothyroidism in Dogs Diagnosed?
Blood tests measuring the amount of circulating thyroid hormone are the most common method for diagnosing the disease. One can measure the total T4 (TT4) or the free T4 (fT4) and you would expect those levels to be low in a hypothyroid dog. Thyroid stimulating hormone (TSH) can also be measured and should be high in a hypothyroid dog. Unfortunately, none of these tests are 100% accurate and hypothyroidism is often over-diagnosed. TT4 can be artificially lowered in sick animals (called “euthyroid sick syndrome”) and dogs on certain drugs including steroids, phenobarbital and sulfonamide antibiotics. TSH levels can randomly fluctuate and approximately 30% of hypothyroid dogs may have a normal TSH level and 30% of normal dogs may have an elevated TSH level. The free T4 level by equilibrium dialysis may be the most accurate test of thyroid function in the dog; it is less affected by systemic illnesses and drugs. An accurate diagnosis is dependent upon the clinical acumen of the veterinarian in addition to supportive tests.
How is Hypothyroidism in Dogs Treated?
Treatment is lifelong and consists of supplementing with thyroid hormone, usually in the form of pills. Blood thyroid levels may be measured over the dog’s lifetime to confirm that he or she is getting the proper amount of thyroid hormone. When properly diagnosed and treated, the prognosis for hypothyroid dogs is excellent.
If your pet is exhibiting any of the signs above, contact your veterinarian or nearest MedVet.