Objectives: Feline hyperthyroidism is a common endocrine disorder in older cats. Previous studies have identified nutritional imbalances, thyroid-disrupting compounds, increasing age and being non-purebred as risk factors but the final trigger remains unknown. The purpose of this prospective study was a) to determine the hospital prevalence of hyperthyroidism in a client-owned cat population in Southern Germany, b) to exploit how frequently hyperthyroidism was diagnosed after the initial clinical suspicion and c) to determine putative intrinsic and extrinsic risk factors from the cats' signalment and a questionnaire analysis, respectively.
Methods: Total thyroxine (T4) was measured in sera of 495 cats ≥ 8 years. Prevalence was calculated with a 95% confidence interval (95% CI) Association between signalment and hyperthyroidism was analysed by Student's unpaired-t-test, chi-square test and Mann-Whitney U-test. Level of significance was set at 0.05. Multivariate logistic regression model was used to determine extrinsic risk factors.
Results: Sixty-one cats were diagnosed with hyperthyroidism leading to a prevalence of 12.3% (95% CI: 9.7-15.5). Older (p < 0.001) female cats (p = 0.019; odds ratio 1.9) were significantly more often affected. Domestic shorthair and domestic longhair cats were more likely hyperthyroid than purebred cats (p = 0.016). In 164 cats hyperthyroidism was considered a differential diagnosis and was verified in 20.1% (33/164). In 2.4% (12/495) cases the elevated T4 was an incidental finding. Hyperthyroid cats were more likely to be fed with moist cat food from aluminum tins (p < 0.013) compared to non-hyperthyroid cats.
Conclusion and clinical relevance: Older, female non-purebred cats are predisposed to hyperthyroidism which is frequently diagnosed after the initial clinical suspicion leading to a prevalence of 12.3% among the study population. Components of the aluminum tins or the moist food itself or both may play a role in the etiopathogenesis.
Keywords: Cat; endocrinopathy; questionnaire; thyroxine.