When deciding why a cat starts to act strangely, hyperthyroidism is one possible cause. “The first signs may be dramatic”1. The increase in thyroid hormones tends to increase appetite. Whereas at one time a cat was a picky eater, he now wolfs down his food. He may look for and demand more food. Secondly, there will be an increase in activity – restlessness and irritability.
The older cat will stop snoozing in the sun and race around like a kitten. Other signs are weight loss despite eating more (see photo), panting and vomiting. A bump under the chin may be seen (enlarged thyroid gland).
These signs in behavior, health and anatomy are fairly clear cut. They should be apparent. After all the vets call the signs “dramatic”.
So if your cat has suddenly started to behave strangely, one of the home tests you can apply is to check behavior against those listed above to eliminate or diagnose hyperthyroidism.
Note: this disease is “almost always associated with a cancer” and they usual occur in older cats. The cancers cause increased thyroid production. Pointed Persian cats (Himalayans) and Siamese “have a lower risk for this problem”1.
Passive smoking can be a cause.
Note 1: Cat Owner’s Home Veterinary Handbook, 3rd Edition, pages 529-530