Hyperthyroidism is a progressive disease with a slow, subtle onset, becoming more obvious with time. Early signs may be hard to recognise because the increased appetite and high levels of activity often seen are not always recognised as abnormal. The gradual deterioration in coat and body condition can also be wrongly attributed to the "normal signs" of aging.
Thyroid hormones control the speed of your cat's metabolism, but when in excess, can cause a range of signs. The more thyroid hormone produced, the higher the metabolic rate and the more calories your cat burns.
Common signs include:
Not all of these signs will occur in every cat with hyperthyroidism.
Poor body condition is a common sign of hyperthyroidism.
Hyperthyroid cats might be nervous or aggressive.
An enlarged thyroid gland is sometimes visible but more often can be felt.
Photographs: Courtesy of Dr Hans Kooistra, Utrecht University