The thyroid glands produce thyroid hormones, which regulate the metabolism. Hyperthyroidism is a condition of overproduction of thyroid hormones and increased metabolism. All the body processes are accelerated and the body burns energy fast. The disease is common especially in older cats and it is possible that diet and environmental factors are responsible for the high incidence.  

Signs and mechanism

Common sign is progressive weight loss (despite ravenous appetite and increased intake of food), increased water consumption and urination and possibly periodic vomiting or diarrhea. Cats may be hyperactive or hypoactive and display behavioral alterations.

The thyroid hormones regulate many organs and systems, such as the heart, the liver, the digestive and nervous system. Affected cats often develop heart problems and high blood pressure. If left untreated the disease progresses and the cat may die of emaciation or heart failure.  


A blood test will show a high level of one of the thyroid hormones, as well as indication of organ malfunction. Other helpful tests are urine analysis, x-rays, EKG, blood pressure determination, and ultrasound.  


There are three choices for treatment:  

1. Radioactive iodine is injected and destroys all abnormal thyroid tissue. Treatment requires one or two weeks of hospitalization at a veterinary hospital licensed to administer radiation therapy. Sometimes, but not always, the expense can be greater than for the other options. 

2. Surgical removal of the affected thyroid portion is effective. There is however a degree of risk involved. The cat is generally hospitalized for one night following surgery. The expense may be in the range of radiation treatment.  

3. Oral medication such as Methimazole, are commonly used. A small number of cats may develop reactions or side-effects (vomiting, lethargy, anorexia, fever, and anemia). The drug must be given for the remainder of the cat's life. Periodic blood tests must be done to keep the dosage regulated. This type of treatment is appropriate for the cat that is a poor surgical risk due to other health problems or is exceptionally old.  


The  prognosis is fairly good for cats undergoing treatment. They regain weight and normalize their metabolism and organ function and enjoy longer quality lives.


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