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Knowns and unknowns of feline hyperthyroidism

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CURRENT understanding of feline hyperthyroidism, as well as different approaches to treatment and management, were discussed at a symposium held in Barcelona in May this year. Called ‘The rise and fall of thyroxin’, the meeting was organised by Hill's Pet Nutrition to mark the launch of its product y/d Feline, an iodine-restricted diet to help in the management of the condition.

Discussing historical and epidemiological aspects, Andrew Sparkes, veterinary director of the International Society of Feline Medicine, noted that, although feline hyperthyroidism is currently considered the most common endocrine disorder of cats worldwide, this was not always the case. The first confirmed report in the literature was in the USA in 1979. This was followed by ‘an explosion’ of other reports from countries including the USA, the UK and New Zealand. Although one or two earlier pathological studies had sometimes identified thyroid nodules or masses in cats, these were rarely, if ever, associated with clinical signs, and all the epidemiological evidence suggested that this was a new condition that emerged in the 1970s and rapidly increased in prevalence.

Epidemiological studies were relatively thin on the ground and not directly comparable. Nevertheless, some had provided convincing evidence of variations in the prevalence of feline hyperthyroidism between countries. Epidemiological studies had also sought to identify risk factors for the disease. Different studies had identified different risk factors, but not consistently, although some risk factors were common to a number of studies. These included: an increased risk with age; a decreased risk in Siamese (and related Himalayan) cats; and an increased risk in cats that consumed canned cat food, especially ‘pot-top’ canned food. However, Dr Sparkes pointed out, epidemiological studies could not demonstrate cause and effect and any apparent association could simply be coincidence. For example, the apparent association with canned food could …

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