Feline hyperthyroidism: A descriptive and case-control study

The frequency of diagnosis of feline hyperthyroidism has increased dramatically since the late 1970s. Whether this increase reflects enhanced diagnostic acumen or an actual increase in the incidence of this disease, or both, is unknown. It seems likely, in view of the distinctive nature of the signs and the lack of evidence of thyroid enlargement and clinical signs in previous feline necropsy series, that feline hyperthyroidism is truly occurring with increased frequency today.

A case-control study was undertaken to identify possible risk factors for this disease. Owners of 56 cats with feline hyperthyroidism and 117 controls were questioned about their cats' exposure to various potential risk factors (e.g., diet, medications) and these exposures were compared. Elevated odds ratios were associated with regular treatment with flea sprays or powders, living strictly indoors and having reported exposure to lawn herbicides, fertilizers or pesticides. Cases were also more likely to receive canned food and were less likely to be Siamese than controls. The relevance of these factors to the etiology of feline hyperthyroidism is discussed.