A cat with overactive thyroid glands will be thirsty and hungry but at the same time lose weight. He may be restless or irritable. His heart rate may be up and his coat may look unkempt. Cat owners should look out for these signs in a middle-aged or elderly cat because hyperthyroidism is the most common endocrine disorder in middle-aged and older cats and a very common disorder in older cats generally.
Most cases of hypothyroidism in cats are caused by a benign form of cancer. The glands become enlarged. Interestingly, one possible cause may be exposure to second-hand cigarette smoke. Even third-hand cigarette smoke can cause cat health problems. If you are a smoker and look after a domestic cat, you may wish to consider this potential health issue which you may not have been aware of. Also, interestingly, Himalayan and Siamese cats have a lower risk to this particular health problem.
The early signs may be quite noticeable and even dramatic. There will be an increase in appetite. If your cat was a finicky eater, she will now wolf down the food no matter what it is. If your cat is a good door opener you may find that she starts to open cupboards looking for more food. In parallel with an increased appetite your cat is likely to become more active. So if you have laid-back, lazy cat who likes lying around in the sun you may find that she is now flying around the house.
Veterinarians may be able to feel a lump in one of the two thyroid glands. There will be blood work to check whether thyroid hormone levels are elevated. Kidney function will be checked. The heart should be checked because it can be damaged by the higher metabolic rate caused by hyperthyroidism.
Feline hyperthyroidism can be treated. The vet will prescribe an oral medication called methimazole. This lowers hormone production. It is given daily. I don’t know whether the medicine is easy to administer. It should be as it is given daily. Your vet may discuss surgery to remove a cancerous gland and if both thyroid glands are removed your cat will need “supplemental thyroid” for the rest of his/her life.
Another option for treatment is the use of radioactive iodine which destroys the cancerous tissue. The cat has to stay in a treatment centre for 7 to 25 days under this form of treatment. Cats undergoing this treatment will need supplemental thyroid for the remainder of their lives.
Hyperthyroidism is especially treatable when it is caught early and provided the heart and kidneys have not been damaged. Rarely, the cancer which causes hyperthyroidism will not be benign and in which case the prognosis is very poor. Note: hyperthyroidism rarely results in kidney disease directly but both kidney disease and hyperthyroidism often occur together. Managing hyperthyroidism can sometimes have a detrimental effect upon kidney function.
Sources: Myself, International Cat Care, The Courier-Tribune and Cat Owner’s Home Veterinary Handbook.