Causes of Hypothyroidism in Dogs

Hypothyroidism in dogs is a condition where the thyroid gland produces less thyroxine than required for regulating various metabolic functions in your dog’s body. Thyroxine affects almost every body function, and without the appropriate levels of thyroxine, the various systems in the body become sluggish and don’t operate efficiently. Impairment of the thyroid gland can be brought on by either primary or secondary causes and typically occur from age 4 to 10.

Primary Causes of Hypothyroidism

Most cases of hypothyroidism fall under the primary cause category. Primary cases are those where the thyroid gland has tissue damage caused by conditions directly dealing with the thyroid. These include problems from inflammation, degeneration or attack by tumor.

• Inflammation of the thyroid gland includes lymphocytic thyroiditis. The dog’s immune system mistakenly attacks the thyroid gland, causing irreparable damage to the gland’s tissue.
• Idiopathic follicular atrophy is the degenerative cause of hypothyroidism. This degenerative disease attacks the thyroid gland without inflammation of the tissue. Although the cause is unknown, idiopathic follicular atrophy is suspected to be the end stage of thyroiditis.
• Tumors are rare, but can impact the thyroid gland and cause it to produce less thyroxine. In order for the thyroxine levels to be impacted, both lobes of the thyroid gland would have to be affected by the tumor.

Secondary Causes of Hypothyroidism

Secondary causes are those conditions outside the thyroid gland that impact its production of thyroxine. This could be a disease that impacts the brain’s production of thyroid regulating hormones, radiation therapy or surgical removal of the thyroid gland.

• There are certain medications that can cause the thyroid gland to reduce its production of thyroxine. Sulfa-based antibiotics are often identified as a cause of hypothyroidism. The good thing about this cause of the disease is that these instances are often temporary, and adequate thyroxine production will resume once the medication is stopped.
• Conditions that prevent the brain or the pituitary gland from producing sufficient quantities of hormones such as TSH (thyroid stimulating hormones) can bring on hypothyroidism. Conditions such as dwarfism fall into this category, with thyroid deficiencies causing stunted growth in breeds such as Boxers and Giant Schnauzers.
• Surgical removal of the thyroid gland is typically done to remove tumors of the thyroid gland. Without the thyroid gland producing thyroxine, the dog would have to be treated for the rest of his life with daily administration of synthetic thyroxine.
• Radiation treatment of thyroid tumors or radioactive iodine treatments for thyroid tumors can also reduce thyroxine production in the thyroid gland.

Treatment for Hypothyroidism

If your dog is diagnosed with hypothyroidism, in most cases he will have to be treated with synthetic thyroxine for the rest of his life. For those cases brought on by medication, treating with synthetic thyroxine will be temporary and only necessary until the offending medication has left your dog’s system, and natural thyroxine production has resumed.

Causes of hypothyroidism are either a direct impact on the thyroid gland or a secondary condition that indirectly impacts the production of thyroxine. In most cases, your dog will have to be treated with synthetic thyroxine for the balance of his life, but in doing this, his overall health and quality of life can be returned.