Hyperthyroidism

What does this mean?

The thyroid glands are paired structures present in the throat region of your pet. The hormone that they produce has a number of very important roles. These include: regulating metabolism, hair growth, reproduction, muscle tone and strength, to name a few. Therefore, when an animal has a problem with their thyroid glands we end up with a muti-systemic disorder, and the animal often presents with a number of problems.

Both dogs and cats can develop problems with their thyroid glands. Interestingly, dogs usually have underactive thyroids, while cats present with hyperactive thyroids.

The clinical signs we often associate with canine hypothyroidism include:
*lethargy, mental dullness, inactivity, weight gain, intolerance of the cold
*hair loss (often symmetrical), dry brittle coat, increased pigmentation of the skin, unexplained poorly responsive external ear infections
*failure to cycle, small testicles, poor libido.

Often these signs develop gradually and owners can be unaware of the subtle changes in their dogs appearance and behaviour.

There are a number of tests that can be performed to determine if your pet has a thyroid problem. The simplest test involves measuring the level of active thyroid hormone in the blood. A thyroid concentration which falls within the normal range is suggestive of normal thyroid function, a low thyroid level is suggestive of hypothyroidism.

If only it were as simple as this.

There are many variables that can affect the thyroid levels in the blood. These include concurrent illness, drug administration (especially corticosteroids), body size and age. We therefore look at the whole picture when determining whether a particular patient has hypothyroidism. The animals history, clinical signs and laboratory results are all considered before a diagnosis is made. Sometimes, if it is still equivocable in these situations we recommend a therapeutic trial.

Treatment involves providing a thyroid supplement. An increase in mental alertness, activity and appetite are usually the initial signs of improvement and are often seen within the first week of treatment. Changes in the skin and hair coat commence within a month of starting treatment, however, it may be a number of months before there is complete regrowth of the hair.

We recommend that the thyroid levels be re-tested a month after commencement of treatment. The dose of medication is adjusted accordingly and continued indefinitely. Thyroid levels should be tested every six to twelve months.

Prognosis for dogs with hypothyroidism given proper thyroid replacement therapy is good and life expectancy is expected to be normal.

Dr Lucy Micklethwraite