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Hyperthyroidism: Frequently Asked Questions

What is hyperthyroidism?

The thyroid is a butterfly shaped gland located on either side of a cat's windpipe. The thyroid produces hormones that regulate metabolism and organ function. With hyperthyroidism, the thyroid becomes overactive, and produces an excess of thyroid hormone.
The thyroid is a gland located in the neck. It plays a very important role in regulating the body's rate of metabolism. Hyperthyroidism is a disorder characterized by the overproduction of thyroid hormone. When excessive amounts of thyroid hormone are in the circulation, the body's metabolism speeds up greatly. Hyperthyroidism is a fairly common disease of older cats. Although the thyroid gland enlarges, it is usually a non malignant (benign) change. Less than 2% of hyperthyroid cases involve a malignant change in the gland.
Hyperthyroidism is a pathological condition resulting from excessive production of thyroid hormones, characterized by increased basal metabolism. Hyperthyroidism is a common endocrinopathy in cats, but is very rare in dogs. Signs and symptoms include weight loss, polyphagia, hyperactivity and elevated liver enzymes.
Hyperthyroidism is common in older cats and is most often caused by a benign tumor called an adenoma. The tumor causes excessive production and secretion of thyroid hormone which can result in life threatening conditions.
Hyperthyroidism is a medical condition in which the thyroid gland produces too much thyroid hormone (called T3 and T4). As the thyroid gland plays a crucial role in regulating metabolism and has effects on nearly all organs in the body, an overactive thyroid can have far reaching effects on health and body functioning.

Is hyperthyroidism dangerous?

Untreated, hyperthyroidism in cats can lead to heart failure or kidney failure and can be fatal.

How can hyperthyroidism be diagnosed?

Your veterinarian can perform blood tests to determine if your cat has hyperthyroidism. Since older cats with the most common signs of hyperthyroidism (weight loss, appetite changes and vomiting) can also have other problems such as kidney disease, diabetes and inflammatory bowel disease, a thorough physical examination, blood testing and urinalysis are usually indicated to allow diagnosis of hyperthyroidism. Radiographs, cardiac ultrasonography and blood pressure determination are also sometimes performed.

What causes hyperthyroidism?

Hyperthyroidism can be caused by: Graves' disease, which is an autoimmune disease Toxic nodules or goiters on the thyroid Excessive thyroid medication given to hypothyroid sufferers Iodine excess Thyroiditis (an inflammation of the thyroid)
The most common cause is Graves’ disease (see Graves’ Disease brochure ). Another cause is one or more overactive nodules or lumps in the thyroid, a condition known as toxic nodular or multinodular goiter . Finally, you may temporarily have hyperthyroid symptoms if you have thyroiditis , which causes the gland to leak thyroid hormone, or if you take too much thyroid hormone in tablet form. 3 DIAGNOSIS
The most common cause is Graves’ disease (see Graves’ Disease brochure). Another cause is one or more overactive nodules or lumps in the thyroid, a condition known as toxic nodular or multinodular goiter. Finally, you may temporarily have hyperthyroid symptoms if you have thyroiditis, which causes the gland to leak thyroid hormone, or if you take too much thyroid hormone in tablet form.
It is not known what causes hyperthyroidism. It is likely dependent on many factors.

What are the symptoms of hyperthyroidism in cats?

Weight loss (typical, but not always) Increased appetite without weight gain Vomiting and diarrhea Increased energy and friskiness More vocalization Demanding food more frequently Drinking more water More frequent urination Decreased appetite (less common, but can be a symptom) Decreased activity (less common, but can be a symptom) Weakness (less common, but can be a symptom) Labored breathing and panting (less common, but can be a symptom)

What are the treatment options for hyperthyroidism?

The three conventional treatment options are antithyroid drugs, surgical removal of the thyroid, and radioactive iodine treatment to disable the thyroid gland. Some practitioners also work with alternative therapies for milder forms of hyperthyroidism.

How is hyperthyroidism in cats diagnosed?

Primarily, diagnosis is made by blood test, measuring the level of thyroxine (T4) in the blood. High T4 levels are considered indicative of hyperthyroidism. Occasionally, if results are not conclusive, a more definitive -- and costly -- test known as Free T-4 may be run. And, some veterinarian will use other tests including T3 levels, T3 suppression test, thyrotropin-releasing hormone stimulation test, and thyroid radionuclide uptake and imaging ("thyroid scans"), to verify a hyperthyroidism diagnosis.

What is involved in surgery for hyperthyroidism?

Surgery -- known as thyroidectomy -- removes the affected part of the thyroid gland. Surgery can be an effective cure, and many veterinarians are capable of performing this surgery. Only a few days of hospitalization is required. Drawbacks, however, include the risk of anesthesia, particularly in an older cat, and the risk of removing the parathyroid glands, which can cause hypoparathyroidism. In some cases, there is also a risk of hypothyroidism if both lobes of the thyroid are removed. ...

How common is hyperthyroidism in cats?

Hyperthyroidism is one of the most common endocrine conditions affecting cats, in particular, older cats over the age of 10. The median age for acquiring hyperthyroidism is approximately 13 years of age, and very few cats develop the condition before the age of 10. Some veterinarians estimate that about 2% of cats over 10 will develop hyperthyroidism, and, due to factors that may include environmental exposures, that number is on the rise.

How is hyperthyroidism treated?

Therapy for hyperthyroidism is generally safe and effective, but no one treatment is best for all patients with hyperthyroidism.

What are the symptoms of hyperthyroidism?

Hyperthyroidism refers to any condition in which the body has too much thyroid hormone. Symptoms may include weight loss, nervousness, irritability, increased perspiration, a racing heart, hand tremors, anxiety, difficulty sleeping, increased bowel movements, fine brittle hair, and muscular weakness—especially in the upper arms and thighs. In Graves’ disease, a bulging of one or both eyes may occur. 2 CAUSES

What causes hyperthyroidism in cats?

In most cats (~99%), a small benign tumor (adenoma) or several small benign tumors (adenomas) are responsible for the overproduction of thyroid hormone that leads to the symptoms of hyperthyroidism. In rare cats (~1.0 %) a functional thyroid carcinoma (cancer) is responsible for the over-production of thyroid hormone that leads to the symptoms of hyperthyroidism. ...

What is hypo/hyperthyroidism?

Hypothyroidism is caused by low blood circulating thyroid hormone or reduced thyroid hormone action synthesis. Signs and symptoms include weakness, fatigue, cold intolerance, constipation, and weight gain. Hyperthyroidism is caused by excessive levels of thyroid hormones in the blood circulation. Signs and symptoms include weight loss, anxiety, palpitations, and heat intolerance.

How is hyperthyroidism diagnosed?

The disease is most commonly diagnosed by determining the blood level of one of the thyroid hormones; the hormone

What are the symptoms of Hyperthyroidism and Hypothyroidism?

Hyperthyroidism symptoms include: Weight loss Increased appetite Nervousness Restlessness Heat intolerance Increased sweating Fatigue Frequent bowel movements Menstrual irregularities Enlarged thyroid Palpitations or irregular heartbeat Hypothyroidism symptoms include: (Early) Weakness Fatigue Cold intolerance Constipation Weight gain Depression Joint or muscle pain Thin, brittle fingernails Thin and brittle hair Paleness (Late) Slow speech Dry, flaky skin Thickening of the skin Puffy face, hands, and feet Decreased tas... ...

What is Feline Hyperthyroidism?

Hyperthyroidism is the clinical syndrome that exists when there is overproduction of circulating thyroid hormone, which is the hormone that regulates the body’s metabolism. This means that hyperthyroid cats have very high metabolism. Feline hyperthyroidism is very common in older cats. Because the thyroid hormone affects the whole body’s metabolism and body systems, if this disease goes untreated, multiple organ systems may be affected and damaged. ...

Hyperthyroidism in cats. What is it?

Hyperthyroidism, or overactive thyroid glands, is a common disease of older cats. It can easily be overlooked as many affected cats show few signs early in the course of the disease. Starting at age 8, we recommend annual testing for thyroid disease. Affected cats can have signs which include rapid heart rate, weight loss, excessive appetite and thirst, vomiting and increased litter box habits. ...

What is the cause of hyperthyroidism?

The most common cause of hyperthyroidism is an autoimmune disease known as Graves' disease. It can also be the result of nodules (lumps in the gland) that cause an overproduction of TH. Hyperthyroidism also can develop during or after pregnancy.

What are the risks of Graves’ Disease/hyperthyroidism to the mother?

In addition to the classic symptoms associated with hyperthyroidism, inadequately treated maternal hyperthyroidism can result in early labor and a serious complication known as pre-eclampsia. Graves’ disease often improves during the third trimester of pregnancy and may worsen during the post partum period.

What is thyroiditis and how is it a cause of hyperthyroidism?

Thyroiditis is inflammation of the thyroid gland. It generally occurs after a viral illness (which is known as subacute thyroiditis) or a pregnancy (postpartum thyroiditis). No specific virus or bacteria has been identified as causing the condition. This condition is temporary, but runs through a cycle of about six to three months. First, the thyroid will release too much thyroid hormone, resulting in hyperthyroidism. ...

How do cats get hyperthyroidism?

The main way cats develop hyperthyroidism is due to development of a benign tumor, known as an adenoma, in their thyroid gland. The tumor secretes excess thyroid hormone, creating the condition of hyperthyroidism.

Does hyperthyroidism play a role too?

Patients with hyperthyroidism can have some cardiac problems and may have an abnormality of heart rhythm, the most common one being atrial fibrillation.

Are there any contraindications to treating hyperthyroidism?

The most significant concern is unmasking underlying renal disease, which although unlikely is a potential side effect with ANY treatment option.
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