Hypothyroidism in Dogs

Canine Overactive Thyroid

Portrait of black dog lying in yard
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Could your dog have hypothyroidism? You may have heard that humans can develop thyroid disease, but dogs can get hypothyroidism too. Hypothyroidism is an endocrine disease that is characterized by a deficiency of thyroid hormones. Commonly occurring in both dogs and humans, hypothyroidism causes a decreased metabolic rate and can lead to a multitude of systemic complications. 

Regular thyroid checks are an important part of your dog's routine wellness visits.

Your vet may be able to detect abnormal thyroid levels before your dog even becomes sick.

Thyroid Disease in Dogs

In mammals, the thyroid gland is found in the neck area. The dog's thyroid is divided into two lobes that lie on either side of the trachea (windpipe) below the larynx (voice box). The lobes look a bit like small deflated balloons, but they have a large role in regulating the body's metabolism. The pituitary gland regulates the production of thyroid hormones by producing and releasing thyroid stimulating hormone (TSH) as needed. Then, the thyroid gland produces thyroid hormones called T4 and T3 that are utilized throughout the entire body.

Hypothyroidism is sometimes called underactive thyroid.  If the thyroid does not produce the needed amount of hormones, the metabolism slows and many of the body's normal processes are disrupted. In dogs, thyroid disease is almost always hypothyroidism.

Hyperthyroidism (overactive thyroid) occurs in cats but is not typically seen in dogs. Unfortunately, an overactive thyroid in a dog is usually a sign of thyroid carcinoma, a cancerous thyroid tumor.

Causes of Hypothyroidism in Dogs

There are a number of potential causes of hypothyroidism in dogs, and the exact cause usually cannot be determined.

Most commonly, canine hypothyroidism is immune-mediated. Basically, the immune system attempts to destroy the thyroid, often resulting in atrophy of the gland. Some dogs are genetically predisposed to the disease, so this is something you can investigate if you know your dog's parents or littermates. Certain dog breeds are at a greater risk for hypothyroidism, such as Golden Retrievers, Irish Setters, and Cocker Spaniels.

Hypothyroidism can occur in a dog of any age, but it is most commonly seen in dogs from four to ten years of age. Gender does not appear to affect risk for hypothyroidism, but some evidence suggests that the disease can occur more commonly in spayed females than intact females. In rare cases, hypothyroidism may be congenital, meaning the disease was present at birth.

Be an advocate for your dog's health by visiting your veterinarian often and taking steps to keep your dog healthy. You may be able to help detect hypothyroidism before it becomes a serious heath problem.

Hypothyroidism Symptoms in Dogs

Canine hypothyroidism can manifest itself in a variety of ways, and the signs may be vague. Unfortunately, these symptoms can also indicate the presence of another disorder, so be sure to consult your vet if you notice any signs of illness.

The most common symptoms of hypothyroidism include the following:

  • Obesity/weight gain
  • Hair loss on body and/or tail (rat tail appearance)
  • Dull, dry hair coat
  • Skin issues, such as infection or flaking
  • Otitis (ear infection)
  • Lethargy and/or weakness
  • Behavioral changes

Less common but potentially serious complications of hypothyroidism include vestibular dysfunction (vertigo) and other neurological disorders, heart problems, and various health issues associated with obesity.

One or more of the above symptoms may occur in hypothyroid dogs, but even dogs with no symptoms can have the disease. For this reason, your dog should visit the vet for a wellness exam and routine blood work at least once or twice a year.

Diagnosing Hypothyroidism in Dogs

If you suspect that your dog has hypothyroidism, you should schedule an appointment with your veterinarian.

By providing an accurate, thorough history to your veterinarian, you can help detect hypothyroidism in your dog. The next step for your vet to perform a complete physical examination on your dog. In order to reach a diagnosis of canine hypothyroidism, your vet must test the thyroid hormone levels in the blood. In most cases, your vet will begin by testing the T4 level. In theory, a low T4 indicates hypothyroidism, but diagnosis is not always this simple. Sometimes the T4 can fall in a gray area and further testing is necessary. In addition, certain medications can interfere with the T4 levels.

Your vet may recommend other blood tests before making a definitive diagnosis. These include measurement of free T4 (the T4 circulating "freely" through the bloodstream) and TSH. Low levels of free T4 are consistent with hypothyroidism. High levels of TSH also indicate hypothyroidism because the pituitary gland will often produce excess TSH in an effort to stimulate the thyroid gland.

Not all cases of hypothyroidism cause abnormal levels in all three primary tests. Hypothyroidism is diagnosed with a combination of blood tests and patient history. Additionally, there are other diseases that cause similar symptoms, so what seems like hypothyroidism at first could be a completely different issue. This is why it is important to communicate with your vet. Discuss all of your pet's symptoms and ask about your diagnostic options.

Hypothyroidism Treatments for Dogs

There is no known cure for hypothyroidism, but the disease is generally easy to manage with medication. Typically, hypothyroid dogs are prescribed synthetic thyroid hormone (T4) to be given orally one to two times daily. The drug names for these thyroid supplements are levothyroxine or L-thyroxine. Common brand names for levothyroxine and L-thyroxine are Soloxine and Thyro-Tabs, respectively. However, other brand names and generic forms are available. In rare cases, liothyronine (T3) is prescribed for dogs that are unable to convert T4 into T3.

The good news is that there are virtually no side effects associated with the usage of thyroid supplements. As with any medication, accidental overdose can occur. Symptoms of overdose include excess drinking and urinating, restlessness, panting, diarrhea and increased appetite.

Hypothyroid dogs must be treated for life. While the cost of thyroid supplements is fairly low, it does add up over time. Expect to spend about $30-60 per month on medication (depending on dosage and brand). This does not include the cost of periodic blood monitoring. Be sure to factor costs into your pet budget.

There are no herbal, homeopathic or home remedies that are effective as alternatives to synthetic thyroid hormone supplements. However, some remedies may be helpful in conjunction with thyroid supplementation. Talk to your vet about the options for your dog.

Monitoring the Hypothyroid Dog

As the owner of a hypothyroid dog, your job is to do your best to keep his disease under control. Your vet will recommend routine blood work to check thyroid levels. When treatment first begins, blood tests will be needed every few weeks until the disease is under control. Once the hypothyroidism appears to be regulated, most vets recommend checking thyroid levels every six months (possibly every year if your dog has done well long-term). Over time, it is normal for your dog's prescribed dose to change. When the dosage is adjusted, blood levels may need be checked more often at first.

Be sure to keep track of changes in your dog's health, appearance or behavior. Contact your vet if you notice any signs of illness, particularly those signs associated with hypothyroidism or thyroid supplement overdose.

Fortunately, most dogs with hypothyroidism can lead long, healthy lives when properly treated and monitored. Keep your dog healthy and stay in touch with your vet about your dog's condition