Autoimmune Thyroid Disease in Dogs

Autoimmune thyroid disease is the inherited form of hypothyroidism, suspected in more than 90 percent of cases in dogs. There is no way to determine the difference, but the strong genetic component indicates that more tests should be done on dogs who might be bred.

Symptoms of Hypothyroidism

The thyroid gland produces hormones that are instrumental in regulating many processes in your dog's body, the most important being metabolism. Though research indicates that symptoms may began in adolescence, the symptoms are often subtle and aren't detected until middle to old age.

Symptoms of hypothyroidism vary from dog to dog, but include:

  • Weight loss
  • Lethargy
  • Hair loss
  • Dry coat
  • Excessive shedding
  • Cold intolerance
  • Exercise intolerance
  • Low heart rate
  • High cholesterol
  • Sudden behavioral changes, such as increased aggression
  • Anemia

In serious cases, in which the symptoms go undetected for long periods of time, your dog may suffer from seizures, cardiac irregularities, corneal ulceration, loss of smell or taste and chronic hepatitis.

Autoimmune Thyroid Disease

New research has shown that more than 90 percent of cases of hypothyroidism can be attributed to an inherited genetic disorder known as autoimmune lymphocytic thyroiditis. As with other genetic autoimmune disorders, thyroiditis causes the body to attack its own immune system, rendering certain systems inactive.

In the case of thyroiditis, this affects the production of T3 and T4, the hormones produced by the thyroid gland. Because the thyroid regulates growth and development, it can cause developmental problems if symptoms begin during puberty, as suspected. Though no other symptoms are present, dogs with autoimmune lymphocytic thyroiditis often have shorter legs and squat bodies compared to others of their breed that developed normally.

Researchers suspect that these genetic autoimmune disorders may be triggered by environmental chemicals, vaccinations and illnesses early in life. However, they also believe that the possibility of acquiring this disease can be detected through blood tests.

Scientists recommend that breeders wait until the dog is old enough for the disease to be detected before breeding one that may have an increased likelihood of passing on thyroiditis. Larger dogs tend to be at higher risk, as toy and miniature breeds are rarely affected.

Breeds that are more likely to acquire the disease are:

  • Golden retrievers
  • Great Danes
  • Doberman pinschers
  • Akitas
  • Rottweilers
  • Borzoi
  • Beagles
  • Boxer
  • Shetland sheepdog
  • Old English sheepdog
  • German shepherd dog
  • Cocker spaniel
  • Labrador retriever 
  • Irish setter

Diagnosis of Hypothyroidism

A definitive diagnosis for hypothyroidism, either form, can only be acquired by a blood test, which measures levels of T3 and T4 in the bloodstream. If these levels are below the normal range, which is quite wide, your dog is hypothyroid. If the levels are too high, he has hyperthyroidism, which is more rare but does occur.

Many experts believe that the normal range is too wide, and if dogs fall outside a more narrow range, they may have thyroiditis that hasn't completely developed yet. Depending on your veterinarian, treatment may start when the levels finally reach outside the normal range or it may begin if your dog shows signs of thyroiditis.

Thyroiditis can be easily treated with medication, which regulates hormone levels in place of the thyroid. However, it can be devastating if left untreated, so visit your veterinarian for a blood test if your dog shows signs of hypothyroidism.