What Causes Hyperthyroidism?
Hyperthyroidism is caused by a benign growth in the thyroid gland that is over-producing T4. It is important to realize that these tumors are almost always benign and represent a form of goiter rather than a form of cancer. Less than three to five percent of hyperthyroid cats have a cancerous thyroid growth.
Many people want to know what caused their cat’s thyroid gland to grow a tumor, benign or otherwise. A study published in the Journal of the American Veterinary Medical Association in March of 2004 shows some interesting information. There is a strong correlation between eating canned food and developing hyperthyroidism later in life; in fact, cats who eat only canned foods from “pop-top” type cans have five times the risk of developing hyperthyroidism relative to cats who eat only dry food. Cats whose diet is 50 percent canned food have 3.5 times the risk of developing hyperthyroidism relative to cats who eat only dry food. It has been speculated that pop-top type aluminum cans are lined with a substance called bisphenol-a-diglycidyl ether, which is transferred into food containing oils or fats. In areas of the world where this type of can is not used for cat food, hyperthyroid is not a common disease. Still, it is important to realize that a good 25% of hyperthyroid cats have never eaten canned foods in their lives, so there is clearly more than one factor at work.
Another study by Dye et al. looked at exposure to bromated flame retardants (polybromated diphenyl ethers specifically) as a factor in the development of feline hyperthyroidism. These chemicals have become largely ubiquitous in the home in the last 30 years, about the same time that feline hyperthyroidism went from an extremely rare disease to an extremely common disease. They looked at PBDE levels in young cats, older normal cats, and older hyperthyroid cats and while they readily found PBDE in the blood samples tested they did not find any difference in levels between cats with or without hyperthyroidism. We mention this study as it received a great deal of press attention when it first came out leading many people to read the “headline” that PBDE’s were being investigated as a cause of hyperthyroidism in cats and miss the conclusion that no significant difference in groups was found. It should be mentioned that indoor lifestyle is definitely correlated to increased chance of a cat being diagnosed with hyperthyroidism. This has led to an assortment of speculations as to why this is:
- Is there a chemical in cat litter involved?
- Is there some other household chemical involved?
- indoor cats simply have a greater likelihood of reaching the age at which hyperthyroidism develops? (While this is certainly true, we do not know if this is the whole story about why indoor cats have an increased rate of diagnosis.)
- Are indoor cats more likely to see the vet and have diagnostic testing while outdoor cats simply go undiagnosed?
Purebred cats, especially the Siamese and Himalayan breeds, appear to have a decreased incidence of hyperthyroidism (meaning they are less likely to develop this condition). This implies that there are genetic factors at work as well.
Why is it so Important to Treat Hyperthyroid Cats?
Hyperthyroid cats frequently experience reduced quality of life through weight loss, muscle deterioration, chronic vomiting or chronic diarrhea. Not all cats experience these signs at the time of diagnosis but there are less visible reasons to treat: heart disease and high blood pressure. These problems can result in heart failure, sudden blindness, or sudden death and all can be prevented with timely treatment for thyroid disease.
Houston Heights Veterinary Clinic
At Urban Animal Vet Hospital, we know how important the health of your pets are to you. Our staff is highly trained and knowledgeable when it comes to diagnosing and treating your loved one. Contact us today to get an appointment for your furry friend.