Hypothyroidism is the clinical condition caused by a deficiency of thyroid hormones. Thyroid hormones are produced by the thyroid glands, which are located in the neck on either side of the trachea (windpipe).
Thyroid hormones have numerous effects throughout the body. Perhaps most importantly, thyroid hormones influence the metabolism of most of the body's organs. Deficiency of these hormones causes a reduction in metabolic rate. For example: heart rate slows, mental function is impaired, body temperature decreases, body weight increases, and energy level decreases. Skin problems and hair loss are also common symptoms.
The cause of hypothyroidism is not fully understood, but is thought to be related to destruction of the thyroid gland by the body's own immune system. The immune system — for reasons unknown — apparently "sees" the thyroid gland as foreign and attacks it. Over time, this attack leads to destruction of the thyroid gland. Production of vital thyroid hormones eventually stops.
Hypothyroidism is the most common endocrine disease of dogs. Predisposed breeds include the golden retriever and Doberman pinscher, but numerous breeds can be affected.
Diagnosis is relatively straightforward by a simple blood test. The levels of thyroid hormones are measured in the blood. On occasion, other disease processes or medications may also lower thyroid hormone levels temporarily. If this is suspected, it may be necessary to repeat the blood test at a later time.
Hypothyroidism is easily treated. Treatment involves the daily administration of thyroid hormone (L-Thyroxine) in pill form. Treatment is life-long, since the damaged thyroid gland will never heal and cannot be repaired. The tablets are small and easily administered. Compared to many other medications, thyroid medication is relatively inexpensive.
It may take several weeks for symptoms to improve after medication is started. Energy level usually increases in the first 1-2 weeks. Skin problems may require 6-8 weeks before noticeable improvement is noted. Because hypothyroidism typically develops over time, owners may not appreciate significant problems due to the gradual onset. Many owners are amazed at the dramatic overall improvement in their pet once medication is started.