Hypothyroidism Is the Most Common Hormone Imbalance In Dogs.
–by Elizabeth F. Baird, DVM, CVPP, CCRT, cVM
Hypothyroidism simply means the thyroid glands are producing inadequate amounts of thyroid hormone to meet the needs of the body. Since thyroid hormone directly controls metabolism, it effects essentially every cell in the body. Too much thyroid hor- mone and blood pressure and heart rate increase, the body begins to burn fat and muscle and the pet becomes
skinny and debilitated.
Inadequate thyroid hormone is often manifested by weight gain, lethargy and poor hair coat. Defining the problem creates a few challenges – thankfully treatment is more straight-forward and generally very successful. The first question is why do dogs
(and humans) become hypothyroid? Most often, there is some immune-medi- ated inflammation in the thyroid glands that leads to cell destruction and replace- ment of functional tissue with fibrosis and scar (Hashimoto’s Disease in humans). This phase is often unnoticed and without obvious symptoms. When thyroid levels begin to drop, the master gland in the brain, the pituitary gland, starts dumping Thyroid-Stimulating Hormone (TSH) in the cir- culation to try to stimulate more thyroid hormone production. That may help for a bit, but ultimately, the thyroid glands become “exhausted” and less able to respond and thyroid hormone levels drop low enough to begin to cause problems. Predisposed breeds for hypothyroidism include the Golden Retriever, the Doberman pinscher, the Irish Setter, the Great Dane, the Dachshund and the Boxer. Many mixed breed dogs are also affected and it most often appears in middle-age. (In humans, middle-aged women are the most commonly affected group). The symptoms may vary, and some dogs may be diagnosed
on routine screening tests before the symptoms are obvious. Others have weight gain, lethargy, cold or thickened skin, elevat- ed cholesterol, symmetrical hair thinning or more serious symp- toms that lead to hormone testing. Dogs with allergies and recur- rent skin infections are often worse if they also have a thyroid hormone deficiency even though it is not the primary problem. Testing can become a bit complicated, but test options have
improved in the last few decades. The screening test, a simple T4 thyroid test, indicates if the hormone levels are adequate. If that is normal, typically the pet does not have hypothyroidism. If it is low (or even low normal) further testing is warranted to deter- mine if the hormone output is truly inadequate. The T4 level can drop for other reasons, like certain medica-
tions, breed (Greyhounds) or illness not related to the thyroid, so it’s important to be sure if the problem is really the thyroid levels. This can be confirmed by checking a Free T4 level (by a specific
72 THE NEW BARKER
test method called equilibrium dialysis). This test tells us how much thyroid hormone is truly available to the dog. The Thyroid- Stimulating Hormone is often tested in a serum thyroid profile as well. If it is high, the thyroid function is likely declining even if the circulating levels are still adequate at that moment. They will likely fall in the future as the thyroid glands are often ultimately unable to produce enough hormone despite the stimulation from the pituitary gland. Fortunately, the treatment is more
direct than making the diagnosis. Thyroid hormone supplementation is simple, but it is for life. The thyroid gland rarely recovers and returns to normal function. Indeed, the gland’s output can continue to change later, so the individual dog’s level may change over time and the dosage may require periodic adjustment. Not only is a low thyroid hormone level
problematic, but excessively high levels are also potentially harm- ful to the pet. Typically, dogs are started on twice daily medication and
their values are rechecked after two to four weeks to see if the medication’s initial dose has their level back into the “sweet spot” of normal circulating T4 levels. This is most often measured four to six hours after the morning pill (peak dose) or first thing in the a.m. when the medication is due (lowest level or nadir). Either method works, but it must be consistent each time to monitor the individual properly. Once the ideal dose as been achieved, the levels are typically monitored twice yearly to verify adequate control. If the dog has sudden changes in weight, lethargy, hair coat or skin problems, a spot check may be warranted between the normal scheduled rechecks. Dogs with hypothyroidism are typically managed readily
with medication and go on to live normal lives without ill effect. It can be a bit more tricky in breeding animals as fertility is very sensitive to hormone imbalances, but pets that are not being bred typically are very responsive to hormone therapy and live out their lives with no symptoms of disease as long as they receive an appropriate dose of thyroid hormone. If there is any “good” hormone imbalance, this is certainly the best of the batch.
U
Dr. Elizabeth Baird is certified in pain management, canine rehabilitation and veterinary medical acupuncture. She is the Practice Owner of Country Oaks Animal Hospital & Boarding Kennel, Palm Harbor: 727.785.6524 and Steele Pain Management Rehabilitation Center:
727.785.HURT.
CountryOaksAnimalHospital.com
www.TheNewBarker.com
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