Evaluation of environmental, nutritional, and host factors in cats with hyperthyroidism

The pathologic changes associated with hyperthyroidism (adenomatous hyperpl asia, adenoma of the thyroid gland) have been well characterized in cats, b ut the pathogenesis of these changes remains unclear. In this research, we undertook a case-control study to search for potential risk factors for thi s disease. Owners of 379 hyperthyroid and 351 control cats were questioned about their cats' exposure to potential risk factors including breed, demog raphic factors, medical history, indoor environment, chemicals applied to t he cat and environment, and diet. The association between these hypothesize d 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 diminished risk of developing hyperthyroidism. Cats tha t used litter had higher risk of developing hyperthyroidism than those that did not. Use of topical ectoparasite preparations was associated with incr eased risk of developing hyperthyroidism. Compared with cats that did not e at canned food, those that ate commercially prepared canned food had an app roximate 2-fold increase in risk of disease. When these 4 variables (breed, use of cat litter, consumption of canned cat food, and use of topical ecto parasite preparations) from the univariate analysis were selected for furth er study as candidate risk factors and analyzed by multivariate conditional logistic regression, a persistent protective effect of breed (ie, Siamese or Himalayan) was found. In addition, results suggested a 2- to 3-fold incr ease in risk of developing hyperthyroidism among cats eating a diet compose d 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 did not retai n a strong association. The results of this study indicate that further res earch into dietary and other potentially important environmental factors (e g, cat litter) is warranted.