Signs and Symptoms

Dog hyperthyroidism is an endocrine disease that causes overproduction of the hormone thyroxin. The presence of excessive amounts of this hormone then affects the animal's entire system, causing many problems. While this condition is quite rare in dogs and is far more prevalent in cats, it does occasionally affect canines. If you're concerned that your canine companion may be suffering from hyperthyroidism, there are a number of characteristic warning signs that you can look out for.

One of the most common and most noticeable symptoms of canine hyperthyroidism is weight loss despite an unusually ravenous appetite. If your pet is eating more than normal and yet seems to be getting thinner and thinner, you should have him or her checked out for this endocrine condition. Sometimes dogs with this disease will eat so quickly that they end up vomiting. Some pets may also experience diarrhea. Also, excessive thirst may accompany the characteristic voracious appetite.

Other very common warning signs of this disease include hyperactivity and nervousness. Your pet may become more active and restless than normal and may also show signs of irritability. These symptoms are often accompanied by an elevated heart rate. In addition to beating faster, an afflicted dog's heart may also exhibit stronger beats, which you may be able to feel by placing your hand against your dog's chest. Some dogs that are suffering from hyperthyroidism also tend to breathe more rapidly than usual.

At times, a canine with this endocrine disease will also experience changes in its coat. For example, a dog's fur may become dull and appear unusually unkempt. Thus, if you notice that your pet is displaying any of the above symptoms, he or she may be suffering from the production of too much thyroxin that is caused by hyperthyroidism. If you suspect that your dog may indeed be suffering from this condition, it's important to contact your veterinarian as soon as possible.


When a case of canine hyperthyroidism is suspected, a veterinarian will make a diagnosis based upon clinical signs and blood tests. First of all, the doctor will speak to you as the pet owner about your dog's behavior at home and the warning signs that you have observed. Then the practitioner will conduct a physical exam, checking for symptoms such as an enlarged thyroid and an elevated heart rate. These steps will then be followed by blood tests.

General blood tests will show whether or not there is a stress response in your pet. In such cases, the blood sample may show elevated levels of red blood cells and some white blood cells. At the same time, certain types of white blood cells -- lymphocytes and esinophils -- will appear in lower amounts than normal. Furthermore, certain other substances such as the liver enzyme ALT, glucose, phosphorus, and creatine may also appear in high levels due to complications in other parts of the body that are caused by the hyperthyroidism.

More specifically, a blood test will be conducted to check for levels of the thyroid hormone known as T4. This is a simple technique that is relatively inexpensive; however, it is not always reliable as the results can appear falsely low due to the effects of medication or other illness. As a result, another technique known as Free T4 or FT4 testing may be required. This test is much more reliable and is far more reflective of the thyroid's true state and function. This method of testing is more expensive than basic T4 testing, but it may be required in order to make a confident diagnosis of hyperthyroidism in your pet.

On some occasions, imaging techniques such as ultrasound may be employed by a veterinarian. Ultrasound allows a doctor to examine the physical characteristics of the canine patient's thyroid, revealing masses or other abnormalities. However, blood tests and clinical signs are the most common avenues used to arrive at a diagnosis of canine hyperthyroidism.


The thyroid is one of the major endocrine glands in the canine body. It is a small, double-lobed structure located in the neck that is responsible for producing the hormones thyroxine (T4) and triiodothyronine (T3). These hormones play a role in several physiological systems and functions, including the regulation of metabolism. When hyperthyroidism occurs, this gland becomes overactive and produces higher than normal amounts of thyroid hormones. Most often this overproduction affects the hormone T4, but sometimes it causes elevated levels of T3 or both hormones together.

Since thyroid hormones are involved in numerous physiological functions and pathways, many parts of the body are affected when normal levels of these hormones are not maintained. In fact, since thyroid hormones play an important role in metabolism, hyperthyroidism has an effect on every single cell in the body. This is because every cell requires and burns fuel. However, certain systems and functions are affected more noticeably than others, giving rise to the characteristic symptoms displayed by animals suffering from this endocrine disorder. For example, the increased levels of thyroxine intensify a dog's metabolism, which leads to the weight loss and ravenous appetite that an afflicted animal experiences.

In fact, this condition causes the intensification of many functions in the canine body. In addition to increased metabolism, the high levels of thyroxine will also cause an increased heart rate and higher blood pressure than normal. If this disease goes untreated, these changes can eventually cause the animal's heart to grow in size which leads to a condition known as myocardial hypertrophy. This occurs because the dog's heart is attempting to respond to the increased stress and pressure being exerted upon this organ. Understandably, this secondary condition can be quite problematic, eventually causing cardiac dysfunction.

As a result, it's clear that hyperthyroidism can have serious effects upon many parts of a dog's system. No cell is left untouched by this disease that is characterized by over activity on the part of a canine's thyroid.


While hyperthyroidism may be caused by a variety of factors in humans, cats, and other animals, in dogs it is almost always caused by cancer of the thyroid, or thyroid carcinoma. This disease involves the growth of a cancerous nodule or other mass on the thyroid gland. This type of malignant mass then interferes with the proper function of the thyroid, causing hyperthyroidism and the overproduction of hormones. Nearly all cases of hyperthyroidism in canines are caused by this type of cancer. Thus, if your dog is suffering from overproduction of thyroid hormones due to this endocrine disorder, it's very likely that thyroid carcinoma is at the root of the problem.

Treatment When a dog is suffering from hyperthyroidism, there are three traditional methods of treatment. These include medication, surgery, and radioactive iodine treatment. In the case of medication, daily doses of specific pharmaceuticals can help to prevent the overproduction of thyroid hormones that this disease causes. In most cases, normal levels of hormone production can be reached in approximately one to three weeks. Depending upon your dog's preferences and needs, this type of medication can often be administered in different forms such as in a solid tablet, in liquid form, or as a gel that can be rubbed into the animal's ears.

In some situations, surgery may be required to treat this condition. This technique can involve the removal of either part of the thyroid or the entire gland. Radioiodine treatment is another possibility. This method uses radioactive iodine to kill the overactive cells of the thyroid. While this is considered one of the most effective treatments for hyperthyroidism, not all animals are good candidates for the procedure and a lengthy hospitalization is often required.

In addition to these traditional treatments, some homeopathic remedies can be helpful with regards to calming an overactive thyroid and reducing the symptoms of this disorder. Numerous natural substances have properties that are very beneficial in this respect. For example, bungleweed has properties which inhibit thyroid stimulating hormones, reducing the overactive production of thyroxine and triiodothyronine. This natural substance also relieves the irritability that can sometimes result from hyperthyroidism. It also helps to strengthen certain heart functions, as does hawthorn. Other useful homeopathic ingredients include lemon balm and valerian. These substances relax spasms, relieve tension, and reduce excitability. Homeopathic products geared towards treating canine hyperthyroidism may contain a combination of these ingredients, as well as other natural ingredients which have a beneficial effect upon an overactive thyroid.

If your dog is suffering from unusual symptoms, the most important thing that you can do is to make sure that he or she is examined by a veterinarian immediately. If a diagnosis of canine hyperthyroidism is made, the veterinary doctor can help you to select and implement the most appropriate treatment option for your individual pet.



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