Controlling Canine Hypothyroidism

Although our feline companions can suffer from hyperthyroidism, the majority of dogs with thyroid problems will have the opposite condition—hypothyroidism.

Hypothyroidism occurs when the thyroid glands do not produce enough thyroid hormone. “If a dog is hypothyroid, there is a very slim possibility that a tumor is present. However, in 99% of cases, it is just a dysfunctional thyroid gland,” says James Flanders, DVM, DACVS, associate professor of surgery at Cornell University’s College of Veterinary Medicine.

SYMPTOMS OF CANINE HYPOTHYROIDISM

As with feline hyperthyroidism, the symptoms of canine hypothyroidism vary widely, but the most common are weight gain or obesity, hair loss or poor haircoat, rough or scaly skin, and exercise intolerance. “Hypothyroidism is the most common endocrine disease that we see in dogs, and it is particularly common in many purebreds,” says David Panciera, DVM, MS, DACVIM, a professor at Virginia–Maryland Regional College of Veterinary Medicine at Virginia Tech. Breeds particularly at risk for this disease include Doberman pinschers, English setters, and Rhodesian ridgebacks.

Contact your veterinarian if your pet is exhibiting any of the following symptoms:

• His affection for chasing balls slows down, and he lags behind on walks.
• His hair is falling out, or his haircoat is dull and brittle.
• He sleeps more than usual.
• His skin seems rough and scaly and may have darkened in color.
• He seems to be putting on weight.
• He prefers warm spots and gets cold easily.

WHY TESTING IS IMPORTANT

Canine hypothyroidism can be a subtle disease. “The clinical signs develop gradually,” Dr. Panciera explains, “so a lot of owners don’t recognize that their animal is becoming ill, or they may mistake their dog’s lethargy, weight gain, and inactivity for signs of aging rather than hypothyroidism.”

According to Dr. Panciera, dogs that have hypothyroidism are usually middle aged, but the disease can affect dogs younger than one year. Three to seven years is the average age of onset, which is why testing dogs starting at a young age is essential. 

Regular veterinary visits and routine blood testing can catch hypothyroidism early and improve a dog’s quality of life. 

TYPES OF TESTS

Hypothyroidism is diagnosed by a group of blood tests that help determine levels of thyroid hormones. The most common test is a T4 test, which is a measurement of blood levels of total thyroxine, the main hormone that is secreted from the thyroid glands. Other tests that are run concurrently are TSH (thyroid-stimulating hormone) and free T4. These two tests provide supportive information because T4 levels can vary and may be low due to illness unrelated to thyroid problems.

MANAGING THE DISEASE

Treatment is lifelong supplementation with a synthetic thyroid hormone called levothyroxine; blood tests are used to determine any necessary dosage adjustments. Improvement in attitude and activity level can usually be seen within a week or two. “A lot of the changes are reversible if the dog is given a thyroid hormone supplement,” Dr. Flanders says. “These dogs can do well for years.”

The Less Common Cause of Canine Hypothyroidism

In some dogs, thyroid tumors are the cause of the thyroid imbalance. “A very small percentage of canine cases can be hyperthyroid and have excessive thyroxine, but in most cases they present as hypothyroid,” says Dr. Flanders. “The tumor is often found by palpation first. The owners may notice a swelling in the dog’s neck, or the veterinarian might discover it during a routine physical.”

The thyroid glands are located on each side of the dog’s trachea. If only one thyroid gland becomes cancerous, the dog may have normal thyroid production and only exhibit a mass in the neck. If left unchecked, the lump can grow quite large and can invade the neck muscles, larynx, esophagus, or even the lungs. “The owner may notice that their dog has a cough or problems swallowing, then find the mass,” says Dr. Flanders.

Fortunately, only one gland is usually compromised by the tumor. “Some of these thyroid tumors can be removed when they are enlarged but not very invasive, and the prognosis is pretty good,” says Dr. Flanders. “However, the tumor is usually considered a carcinoma—a malignant form of cancer—so there is the potential for recurrence, even in the ones that can be completely removed.”

For more information about Canine Hypothyroidism, refer to our diseases & conditions library.