Since first reported in the late 1970s, there has been a steady but dramatic increase in the
worldwide prevalence of hyperthyroidism in cats. It is now regarded as the most common
feline endocrine disorder, with diabetes mellitus coming a close second. Not only is there
evidence for an increased worldwide prevalence of feline hyperthyroidism, but also for
geographical variation in the prevalence of the disease. Despite its frequency, the underlying
cause(s) of this common disease is or are not known, and therefore prevention of the
disease is not possible. Due to the multiple risk factors that have been described for feline
hyperthyroidism, however, it is likely that more than one factor is involved in its pathogenesis.
Continuous, lifelong exposure to environmental thyroid-disruptor chemicals or goitrogens in
food or water, acting together or in an additive fashion, may lead to euthyroid goitre and
ultimately to autonomous adenomatous hyperplasia, thyroid adenoma and hyperthyroidism.
This review aims to summarise the available published evidence for the changes observed
in the worldwide prevalence of the disease, as well as risk factors that may contribute to
development of hyperthyroidism in susceptible cats.