As your dog approaches his middle-aged years, your veterinarian may start to order thyroid function panels to your dog's wellness blood testing regimen. Proper thyroid function is essential to your dog's metabolism, and a sluggish thyroid needs to be treated. Learn about the common canine thyroid condition that your veterinarian will be monitoring your furry friend for and how it can be dealt with if diagnosed.

What Is the Thyroid?

The thyroid is a gland that is located in the throat area, near your dog's larynx. The pituitary gland, which is located at the base of your dog's brain, regulates the thyroid gland's production of thyroid hormones. One of these hormones is called levothyroxine, or T4, and this hormone is responsible for the rate of your dog's metabolism. When the amount of T4 hormone in the blood is lower than the normal range, hypothyroidism is diagnosed. When the T4 level in the blood exceeds the normal range, hyperthyroidism is diagnosed. The normal reference range for a T4 level in dogs is between 0.8 and 4.0 µg/dL. While cats are most commonly afflicted with hyperthyroidism, the reverse is more frequently diagnosed in dogs.

Which Dogs Are Affected?

Hypothyroidism can be detected in any dog, but it is most commonly diagnosed in middle-aged to older dogs between the ages of four and 10 years. Certain breeds are genetically predisposed to developing hypothyroidism. Some such breeds include the following:

• Labrador retrievers
• Golden retrievers
• Boxers
• Dachshunds
• Cocker spaniels
• Doberman pinschers
• Greyhounds
• Great Danes
• Schnauzers

Hypothyroidism is seen more frequently in medium and large dogs. Dogs that are spayed or neutered are more commonly diagnosed than those who are intact.

What Causes Hypothyroidism?

Hypothyroidism is most often caused by autoimmune thyroiditis, a condition in which the dog's immune system attacks the tissues of the thyroid gland. Other causes of hypothyroidism include the following:

• Congential hypothyroidism
• Tumor on the thyroid gland
• Iodine deficiency

Whatever the cause, the symptoms of hypothyroidism are the same.

What Are the Symptoms of Hypothyroidism?

Since a low thyroid hormone level results in sluggish metabolism, your dog is unable to burn through calories as quickly, and he will appear to pack on some extra weight. Not all overweight dogs have hypothyroidism, however, so you will need to be on the lookout for additional symptoms, which may include any of the following:

• Patchy hair loss
• Dull coat
• Flaky skin
• Brittle nails
• Lethargy and decrease in activity level
• Muscle weakness
• Decrease in alertness
• Increased incidences of ear and skin infections
• Increased sensitivity to cold temperatures
• Constipation
• Slow heart rate

If your dog exhibits any of these symptoms, your veterinarian will draw a blood sample from your dog to run a thyroid panel. Once your veterinarian reviews the results, he or she will be able to determine if your dog has hypothyroidism, and treatment can be initiated.

How Is Hypothyroidism Treated?

Fortunately, hypothyroidism is neither difficult nor expensive to treat, but treatment will be a lifelong requirement. Hypothyroidism in dogs is treated with oral levothyroxine tablets. Each dog requires his own unique dose based on his blood thyroid hormone levels. Once your dog has been taking the medication for a month or so, your veterinarian will need to run another thyroid panel to determine if the initial dose is having the desired therapeutic results. Alert your veterinarian if agitation, excessive thirst, or excessive appetite occurs. These signs may be indicative that the dose may need to be reduced. Once the correct dosage for your dog has been determined, expect periodic monitoring of your dog's blood thyroid hormone levels for the remainder of his life. Over the course of his remaining years, the medication may become ineffective at the current dose, and a higher dose will need to be prescribed.

Dedicated medicating and laboratory monitoring will enable your dog to enjoy a normal quality of life for the rest of his natural lifespan.

For more information about hypothyroidism and your dog's health, contact your veterinarian or visit a local animal hospital.