Hypothyroidism is a fairly common endocrine disease, the result of an underproduction of T4 and T3 by the thyroid gland -- part of the endocrine system. It can appear in any age dog but is more common in young to middle-aged animals. There is a breed predilection toward this disease in Golden Retrievers.

Endocrine System

The endocrine glands, located in various places throughout a dog's body, are the manufacturers of hormones, which, when released, travel in the bloodstream throughout the body to reach another gland or part of the body. These hormones, sometimes call the chemical messengers of the body, regulate body functions in numerous ways. Because there is a tremendous amount of interaction between hormones, it is often difficult to isolate them.

Thyroid Gland

Located under a dog's chin, this gland makes two main hormones, T4 and T3. T4 (Thyroxine) and T3 (Triiodothyronine) are responsible for increasing the dog's metabolic rate and are necessary for hair growth. The most common problem associated with the thyroid gland in underproduction, resulting in hypothyroidism.

Symptoms

Symptoms of the disease vary but usually include lethargy, fatigue, increased somnolence and a propensity to seek heat. Most dogs also slow down mentally, becoming less alert and excitable. Some dogs gain weight, but others remain at their normal weight or lose.

Hypothyroidism can also produce skin and coat changes including scaling, a dry, sparse coat and sometimes a dark pigmentation of the skin. Some dogs lose a great deal of hair, especially over the neck, hind thighs, flanks and abdomen. Others develop thickened skin folds over their faces and foreheads resulting in a "tragic"" look.

Diagnosis

Diagnosis of the disease is made by blood test, in addition to clinical observation. Hypothyroidism in dogs is treated with daily oral medication that replaces the missing hormone. Usually the disease is permanent and requires lifetime treatment. However, once the disease is being treated, the prognosis is excellent, and the dog's life span should be normal.

PostScript

Golden Retrievers do not always exhibit the classic clinical symptoms of hypothyroidism. It is important for an owner who knows that "something is wrong" with her Golden to continue appropriate testing until the answer is clear. Further, different brands of the thyroid replacement hormone can be more effective for different dogs than others. If your dog does not respond to one, ask your veterinarian to prescribe another rather than just increasing the dosage.

Neurologic Signs Of Hypothyroidism

Veterinary medicine has for the last few decades been studying the possible muscle and nervous system involvement in hypothyroidism, with the conclusion that inadequate thyroid function can, in some circumstances, predispose a dog to a wide variety of abnormalities.

These include muscle cramps, generalized weakness, stiffness, exercise intolerance and facial paralysis. According to Dr. Cheryl L. Chrisman of the University of Florida, facial paralysis alone may indicate hypothyroidism. In addition, seizures, disorientation and circling may be seen in a dog that has developed cerebrovascular atherosclerosis (basically, loss of blood supply to the brain) as a result of (untreated) loss of thyroid function.

Thyroid Hormones and Behavioral Problems
From Dog World, March 1994

Many dog fanciers believe that certain kinds of behavioral problems -- the kinds often refractory to traditional veterinary intervention of behavioral training -- arise because of a dysfunctional thyroid. Specifically, according to Dr. Jean Dodds, the two kinds of thyroid dysfunction affecting behavior are autoimmune thyroiditis and an advanced stage of hypothyroid disease characterized by a hypoactive thyroid.

Dodds believes behavioral problems that develop because of a hypoactive thyroid or thyroiditis are manifested in three ways: heightened proclivity for aggression, extreme shyness or seizure like activity. Dodds implies that thyroid hormones act on the brain to change behavior. Her supposition is that thyroid dysfunction may be "inducing some type of physiological change at the cellular level which leads to aberrant behavior."

However, Dr. Richard Polsky of Animal Behavior Counseling Services in Los Angeles, says there needs to be more research done to pinpoint the exact effects the thyroid hormone therapy has on the dog and exactly why it may lessen behavioral problems.

He states that reduction in behavioral problems brought on through thyroid replacement therapy may be the result of a change in the concentration of another hormone affected by the thyroid and not the thyroid hormones themselves. The thyroid replacements may also make other senses more acute, thereby decreasing the probability that a dog would respond with aggression, fear or seizure like activity. He also states that other important factors, particularly the past experience of an animal, interact with hormones to cause behavioral response.


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