Conference Proceedings, (1998). American College of Veterinary Internal Medicine:
The pathologic changes associated with hyperthyroidism (ie, adenomatous hyperplasia and adenoma of the thyroid gland) have been well-characterized in cats, but the pathogenesis of these changes remains unclear. In this study, we undertook a case control study to search for potential risk factors for this disease. Owners of 379 hyperthyroid and 351 control cats were questioned about their catsI exposure to potential risk factors including breed, demographic factors, medical history, indoor environment, chemicals applied to the cat and environment, and diet. The association between these hypothesized risk factors and outcome of disease was evaluated by conditional logistic regression. Two genetically related cat breeds (ie, Siamese and Himalayan) were found to have a diminished risk of developing hyperthyroidism. Cats who used litter had a higher risk of developing hyperthyroidism than those who did not. Compared with cats whose diets excluded canned food, cats who ate commercially-prepared canned food had an approximate 2-fold increase in risk of disease. Use of topical ectoparasite preparations were associated with increased risk of developing hyperthyroidism. When these four variables (ie, breed, use of cat litter, consumption of canned cat food, and use of topical ectoparasite preparations) from the univariate analysis were selected for further study as candidate risk factors and analyzed by mulivariate conditional logistic regression, a persistent protective effect of breed (ie, Siamese or Himalayan) was found. In addition, results suggested a 2- to 3fold increase in risk of developing hyperthyroidism among cats eating a diet composed mostly of canned cat food and a 3-fold increase in risk among those using cat litter. In contrast, the use of commercial flea products was no longer significant. The results of this study indicate that dietary and other potentially important environmental factors (eg, cat litter) may contribute to hyperthyroidism in cats but further investigation is warranted.