Evidence for Differing Incidences of Feline Hyperthyroidism in London, Uk and Spain

Wakeling J., Melian C., A. F., et al.

Conference Proceedings, (2005). Proceedings of the 15th ECVIM-CA Congress: p.2005


There is much anecdotal evidence that the incidence of feline hyperthyroidism (HTH) varies hugely between different geographical locations. If this were true it could be used as a powerful tool, for comparative epidemiological studies looking at the exposure of cats in high and low incidence areas, to putative risk factors for the development of HTH. The purpose of this study was to test the hypothesis that the incidence of HTH in Spain is lower than that found in London, UK.

A retrospective analysis of the databases from 5 hospitals in Spain (first opinion and referral) and 1 first opinion hospital in London UK was undertaken. Hospitals were chosen that have an interest in feline medicine and that are testing for hyperthyroidism on a regular basis. The number and age of cats visiting each clinic per year for 3 years (2001-2003 inclusive) was determined. The number of new HTH diagnoses per year was determined for each clinic. Cumulative yearly incidence rates for HTH in cats over 9 years old were calculated.

There was a significant difference (P<0.001, independent samples t-test) in the cumulative yearly incidence rate of HTH for all the Spanish hospitals combined (1.53%) and the UK hospital (11.92%) in cats >9 years of age. On average 27.62% of the Spanish senior cats seen were screened for thyroid disease by tT4 measurement (range 11.11-48.54%; data from 4/5 hospitals). The proportion of cats seen that were >9years old was approximately the same in the 2 countries (16.37% & 20.12%). One referral hospital in Spain provided 7/10 of the HTH cases and thus the first opinion yearly cumulative incidence rate for the Spanish hospitals may be lower.

There is some debate whether the apparent geographical differences in the incidence of HTH are genuine or relate to differences in awareness of the disease amongst veterinarians and cultural differences in the willingness of clients to seek and pay for the care of their senior cats. In a recent report from Japan, HTH was diagnosed in 8.9% of animals when random tests were performed on 112 ‘aged’ cats despite the fact the disease was considered to be uncommon and has only been recognised in this country since 1993. This suggests that under-reporting may be a significant problem in some countries. Nevertheless, the present study suggests a marked difference in the cumulative incidence of HTH between Spain and London. A prospective study involving random blood testing of senior cats in Spain and the UK is warranted to confirm the findings of this retrospective study.