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Hyperthyroidism - Excess Thyroid Hormone in Cats

Hyperthyroidism in Cats

 

Hyperthyroidism is a disease caused by overproduction of thyroxine, a thyroid hormone that increases metabolism in the body. The thyroid gland normally produces thyroid hormones in response to stimulation by the pituitary gland, the "master gland" of the body. Thyroid hormones normally increase chemical processes occurring within the cells of the body, especially those related to metabolism; however, in hyperthyroidism, the excessive hormone levels push the cells and body into overdrive, resulting in increased metabolism with concurrent weight loss, anxiety, and diarrhea, among other symptoms.

 

There is no known genetic predisposition for hyperthyroidism, but it is quite common in cats. In fact, hyperthyroidism is the most common hormonal (endocrine) disease in the cat population, often seen in late middle-aged and older cats. (The mean age of discovery is approximately 13 years, with a range of 4-22 years.)

 

Symptoms and Types

 

  • Involves many organ systems due to the overall increase in metabolism
  • Weight loss
  • Increased appetite
  • Unkempt appearance
  • Poor body condition
  • Vomiting
  • Diarrhea
  • Increased thirst (polydipsia)
  • Increased urine (polyuria)
  • Rapid breathing (tachypnea)
  • Difficulty breathing (dyspnea)
  • Heart murmur; rapid heart rate; particularly an abnormal heart beat known as a “gallop rhythm”
  • Hyperactivity
  • Aggression
  • Enlarged thyroid gland, which can be felt as a lump on the neck
  • Thickened nails

 

Less than 10 percent of cats suffering from hyperthyroidism are referred to as apathetic. These patients exhibit atypical signs such as poor appetite, loss of appetite, depression, and weakness.

 

Causes

 

  • Overfunctioning thyroid nodules (where the thyroid nodules produce excess thyroid hormones outside of the control of the pituitary gland)
  • Rarely, thyroid cancer
  • Some reports have linked hyperthyroidism in cats to some canned food diets
  • Advancing age increases risk

 

Diagnosis

 

The signs of feline hyperthyroidism can overlap with those of chronic renal failure, chronic hepatic disease, and cancer (especially intestinal lymphoma). These diseases can be excluded on the basis of routine laboratory findings and thyroid function tests. Your veterinarian will conduct a battery of tests to zero in on a reliable diagnosis.

 

 

Thoracic radiography and echocardiography may be useful in assessing the severity of myocardial disease. Abdominal ultrasound may be useful for exploring underlying renal disease.

 

Thyroid gland scintigraphy (a diagnostic test in which a two-dimensional picture of a body radiation source is obtained through the use of radioisotopes) can be used to diagnose hyperthyroidism and to determine the location of abnormal thyroid tissue. A high concentration of T4 (tetraiodothyronine) in the blood serum is the most common finding, confirming the diagnosis of hyperthyroidism. In some cases, however, the T4 levels may be in the normal range, making a diagnosis of hyperthyroidism more difficult. This is especially true in the early stages of this disease. If your cat is showing the symptoms of hyperthyroidism but the blood tests are not conclusive, you will need to return to your veterinarian for further blood tests.

 

Comments  1

Leave Comment
  • Surgery vs. Medication
    03/19/2017 04:33am

    My cat Pepper was diagnosed with hyperthyroid when he was 13. The hyperthyroid was treated with medication. This worked well until at 18 he got cancer.

    The cancer was difficult, but it was made much more difficult by the hyperthyroid condition. While the two conditions seemed unrelated, the hyperthyroid became unmanageable. Pepper drank water constantly, yowled, and lost a lot of weight. The medication was not entirely effective and he was too old for surgery.

    At 19, Pepper passed away. The doctors were able to extend his life for months after they expected him to pass, but the cancer ultimately was too much. I believe that the hyperthyroid contributed as much or more to his passing than his cancer as the symptoms were debilitating.

    The Doctors did their best and this was an unusual case, but if I had it to do it again I would have Pepper’s thyroid treated with surgery when he was young enough to survive the surgery. If he had not had the weight loss and the other symptoms from the hyperthyroid, he might have lived much longer or at least had a better quality of life as he was treated for the cancer.

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