All Pets Veterinary Clinic


The thyroid gland is a paired organ located in the neck of cats and dogs. It is
responsible for the secretion of a hormone called thyroxine. When the thyroid gland
does not secrete enough thyroxine, a condition called hypothyroidism occurs. This
condition is the opposite of hyperthyroidism, which we discussed last week as the number
one endocrine disease in cats. Hypothyroidism is one of the most common endocrine
disease in dogs. The remainder of this article will discuss the occurrence, signs,
diagnosis, and treatment of hypothyroidism.

Occurrence. Hypothyroidism most often occurs in middle aged, medium or large
breed dogs. It occurs equally in male and female dogs. Laboradors, golden retrievers,
Irish setters, Dobermans, dachshunds, and cocker spaniels have an increased chance of
becoming hypothyroid, but other breeds can be affected as well.

Signs. Hypothyroid dogs can show a wide variety of signs including: lethargy,
inactivity, preference for warm areas (heat seeking), dull coat, slow heart rate,
generalized weight gain, hair loss, thickened skin, pigmented skin, abnormal heat cycles,
decreased testicle size, abortion, clotting problems, diarrhea, anemia, disorientation,
and seizures.

Diagnosis. Because there are such a wide variety of signs, initial diagnosis of
hypothyroidism can be difficult. Blood tests to determine low levels of thyroid hormones
will confirm the presence of hypothyroidism. In addition to determining thyroid levels,
a complete blood count, chemistry panel, etc. may also be done.

Treatment. Hypothyroidism is best treated by supplementing the dog with oral
thyroid hormones. Initially, the dog will be given thyroid hormone pills twice a day.
As the dog’s body becomes used to the medication, once a day dosing is usually sufficient.
Dogs will generally need thyroid hormone supplements for the remainder of their life.

The information provided is for educational purposes only and is not
intended to take the place of your regular veterinarian. Please do not hesitate
to contact your regular veterinarian if you have questions regarding your pet.

Karen Blakeley, DVM, MPH
14 December 2002