Canine Hypothyroidism

Canine hypothyroidism is a disease in which the thyroid gland, the gland in the throat that controls metabolism, malfunctions. The thyroid gland produces two hormones, known as thyroxine (T4) and triiodothyronine (T3). In hypothyroidism, these hormones are underproduced and, as a result, dogs with this disorder have low metabolic rates. This condition may be found in all breeds of dogs, but most commonly develops in medium-and large-breed dogs of middle age. Breeds most often affected include doberman pinschers, Irish setters, Airedale terriers, Labrador retrievers, and greyhounds.

Causes of Canine Hypothyroidism

There are two basic types of canine hypothyroidism, primary and secondary. Primary canine hypothyroidism is almost always caused by autoimmune (or lymphocytic) thyroiditis, an inherited condition that destroys thyroid tissue. Rarely, primary canine hypothyroidism is the result of an idiopathic atrophy of the gland. It is theorized that dietary and environmental factors may be at play in the development of the primary type of this disease. Secondary canine hypothyroidism is caused by another underlying disorder, usually a tumor on the gland.

Symptoms of Canine Hypothyroidism

Hypothyroidism affects dogs in several ways. The most common symptoms include weight gain, dry skin and hair loss. Skin and hair symptoms often occur in a symmetrical pattern. Other symptoms of the disorder include:

  • Constipation
  • Slowed heart rate
  • Lethargy
  • Absence of heat cycles
  • Anemia
  • High cholesterol levels

Dogs with hypothyroidism may also develop deafness or corneal ulcers and the disease may be associated with other disorders, such as von Willebrand's disease and myasthenia gravis. Occasionally hypothyroidism causes behavioral changes, such as unusual aggression. This last symptom has been most clearly documented in German shepherds.

Dogs are routinely tested for thyroid function, but not all dogs whose blood shows a low level of hormones are affected with the disorder. When a dog is suspected of having canine hypothyroidism, more extensive blood tests must be administered to avoid overdiagnosis of the disease.

Treatment of Canine Hypothyroidism

Although canine hypothyroidism is a permanent condition, it can be treated very effectively with administration of thyroid hormone replacements. Dogs with this disorder have to be monitored with regular blood tests and doses so dosage can be altered by the veterinarian as needed. Symptoms can usually be reversed with proper medication.

Dogs at risk for the hereditary form of this condition are not used for breeding.

Additional Resources