by Beth Clark, RN and Raimo Tuomela, DVM
The thyroid gland plays a critical role in endocrine regulation. In simple analogy, thyroid acts as a gas pedal in a car, setting appropriate metabolic speed, directing different processes in the body.
The thyroid secretes two important hormones: thyroxin (T4) and triiodothyronine (T3). About 90% of thyroid secretions are T4, but it is the T3 that is the more "active" of the two.
Most cases of hypothyroidism are the result of autoimmune thyroiditis: the immune system attacks the thyroid gland tissue. For a period of time, the body can compensate by overproducing thyroid hormones. Ultimately, it cannot keep up and outward symptoms develop.
Signs and Symptoms
Hypothyroidism has a myriad of clinical signs:
- Change in coat quality.
- Symmetrical hair loss
- Loss of tail hair (rat tail)
- Weight gain
- Intolerance for exercise
- Chronic ear infection
- Behavioral changes
- Facial paralysis
- Circling behaviors
Changes in coat quality or hair loss are often the first indications of this disease. If hair regrowth occurs, it is often slow and the hair quality is lacking -- dry, dull or discolored. The skin may also become discolored and/or greasy, thick, or possess a displeasing color.
Causes of the Disease
There is a very obvious genetic predisposition to hypothyroidism; the mode of inheritance is unknown.
There is also evidence that environmental factors, such as diet, nutrition and chemical toxin exposure may also play a role in the disorder.
An annual Michigan Panel provides the most complete analysis of endocrine health. Testing for T4 levels alone (common thyroid test) is often inaccurate except in the most advanced cases.
When properly diagnosed, hypothyroidism can be controlled with use of a synthetic hormone supplement, generally in pill form, administered twice daily.
A comprehensive resource may be found on the Orthopedic Foundation for Animals website at www.offa.org.
Hypothyroidism has been reported in 30% of 200 SWDs tested worldwide. Dogs have been reported from: USA, Finland, Belgium, Germany and Sweden.
More than 70% of breeds recognized by the AKC are genetically predisposed to hypothyroidism.