Feline Hyperthyroidism

Jan 28th, 2016
Topics: General Blogs
A 12-year-old spayed female cat presents with a history of vomiting, drinking a lot of water, increased activity, and being more "grumpy" than usual. Her appetite is increased but she's lost several pounds and is now quite thin. Her haircoat is dull and poorly groomed (by herself). She has a normal temperature and the other cats at home are healthy. What is our first suspicion as a diagnosis and how do we test for it?
 
 
 
 
For a cat who presents with this set of symptoms, our primary rule-out is Hyperthyroidism. A simple blood test measuring high total thyroid hormone gives the diagnosis. 
 
Hyperthyroidism occurs typically in middle-aged and older cats. High levels of thyroid hormone are produced by benign nodules on the thyroid gland and less commonly by a malignant tumor. Excessive thyroid hormone causes the symptoms described above and can less commonly cause muscle atrophy, diarrhea, rapid heartbeat, high blood pressure, and heart murmurs. Decreased kidney function or failure often occur together with Hyperthyroidism. 
 
Treating Hyperthyroidism in Cats
 
  •  Medication: A medication called Methimazole is often the first choice for treating hyperthyroidism. Challenges include difficulty of giving pills to cats twice daily and adverse reactions to the medication, which are less common.
 
  • Diet modification: Hill’s Prescription Diet has formulated a special diet called y/d that limits the amount of thyroid hormone that can be made in the body. However, many kitties protest this diet and simply will not eat it. Also, healthy cat housemates should not eat this diet, which causes problems in feeding logistics for many households. 
 
  • Surgery: Removing the thyroid glands is the surgical option in Hyperthyroid cats, however much care must be taken to avoid removing the parathyroid glands that live very close to the thyroid glands, or serious complications can occur. This may also be a cost-prohibitive treatment for many owners.
 

  • Radioactive Iodine Treatment: Injection of radioactive Iodine targets and destroys thyroid tissue but spares the parathyroid tissue. Although considered the “Gold Standard” of treatment, it costs several thousand dollars and is performed at relatively few veterinary institutions. Also, cats with impaired kidney function or other aged diseases are not good candidates for this treatment. 
 
Prognosis
 
Hyperthyroidism remains a progressive illness with medical or dietary therapy, the two treatments that are commonly chosen by owners. The goal of treatment is to slow progression of the disease and to treat secondary problems such as kidney disease. Many cats respond well for a period of time, then reach a refractory period in which the Hyperthyroidism is difficult to be controlled, or the cat declines to poor quality of life and is then put to sleep. 
 
Although the disease limits life expectancy, many cats are able to have quality life with management for many months and even years. We have a kitty who is going on two years with medical management and is doing very well. 
 
Thyroid Hormone and Dogs
 
When it comes to dogs and thyroid disease, dogs most often develop low thyroid levels, called Hypothyroidism.
 
Hypothyroidism is due to an immune system “attack” of the thyroid glands. Thus, dogs are medicated with synthetic thyroid hormone, usually with great results. We typically only find dogs to be Hyperthyroid while medication is being adjusted. 
 
 
 
Dr. Shelby Bradberry
Advanced Veterinary Care