Causes.....Clinical Signs......Diagnosis......Treatment

[NOTE: To appreciate the content of this page, The reader is encouraged to read the thyroid hormone primer before proceeding down this page....]

Introduction (Causes): Feline hyperthyroidism is a disease of middle and older age cats resulting from excessive amounts of circulating thyroid hormones (T4 and T3). The cause is most often associated with benign but functional adenomatous hyperplasia of one or both lobes of the thyroid gland or of extra-thyroid-gland thyroid tissues. These tissues secrete thyroid hormone autonomously, in the absence of TSH secretion from the pituitary gland (see primer for explanation). Rarely (only 1-2%), hyperthyroidism occurs as the result of a malignant, functional thyroid carcinoma.

Clinical Signs: Excessive thyroid hormone results in the stimulation of metabolic process processes in nearly all tissues of the body. There are many potential clinical signs, (see pictorial montage below too) but the most common are:

Other (less common) clinical signs might include:


Treatment of Hyperthyroidism:

Treatment options are medical, surgical and radiaton. The appropriate treatment is selected based on concurrent medical "issues", and potential complications of the treatment, which vary animal to animal. For example, treatment of hyperthyroidism sometimes reveals occult kidney disease, which then manifests as overt renal failure. One proposed explanation for this observation is that the hyperthyroidism, by virtue of its effect on blood pressure forces the kidneys to filter more urine than they otherwise would. Correcting the elevated blood pressure (via treating hyperthyroidism) results in poorer perfusion of the kidneys, and less production of urine. All this is theory and it is possible that there are other, more important direct effects of thyroid hormone on renal function. (Otherwise we should be treating all cats with kidney failure with thyroid hormone!!!). Other potential complications are described below.

Of course, in many instances, cost must be considered a mitigating factor as well.

To reiterate an important point::

 It is essential to determine that occult renal disease is not present prior to any surgical or radiation treatment

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