Feline Hyperthyroidism
Hyperthyroidism is a relatively common condition that can affect middle age to older cats. It typically occurs due to overproduction of thyroid hormone. In most cases, the cause is a benign growth on the thyroid gland.
Clinical signs:
Thyroid hormone is involved in controlling an animal's metabolic rate, so an increase in thyroid hormone results in an overall increased metabolic rate. Cats with hyperthyroidism often have weight loss, a ravenous appetite, increased thirst/urination, and sometimes chronic gastrointestinal upset. Sometimes, they will seem restless or agitated. If left untreated, over time, hyperthyroidism can cause muscle wasting and changes to the heart.
Diagnosis:
If your veterinarian suspects hyperthyroidism they will typically run a blood panel that includes a T4 level. If the T4 level is increased, it is likely the cat has hyperthyroidism. However, if this value is in the gray zone or only minimally elevated, the veterinarian may recommend checking additional thyroid hormones to confirm the diagnosis.
Treatment:
There are three main treatment options for hyperthyroidism.
One treatment option is a medication called methimazole that suppresses the over production of thyroid hormone. This medication typically needs to be taken twice daily and is something the cat will need to stay on forever.
Radioactive iodine treatment is another option and the only way to "cure" hyperthyroidism. This treatment involves injecting the cat with radioactive iodine, which damages the overactive thyroid tissue and returns the cat's thyroid hormone levels to normal. This procedure is typically performed at a specialty hospital, and the cat is hospitalized for several days after the procedure until their radiation levels have decreased enough to be sent home.
The third treatment option is feeding an extremely iodine restricted diet called Hill's y/d. This diet works by starving the thyroid gland of iodine, which is necessary for thyroid hormone production. Cats that are eating this diet cannot get any other type of food, treats, etc or the diet will not work.
Additional considerations:
Cats with hyperthyroidism may develop hypertension (elevated blood pressure), so your veterinarian may recommend checking blood pressure.
Additionally, many cats with hyperthyroidism also have kidney disease, but this may be “masked” by hyperthyroidism. In some cases, once they are treated for hyperthyroidism, the kidney disease becomes unmasked and may require further treatment (typically, we start with a prescription diet). We still definitely recommend treating hyperthyroidism, but we do want to monitor the kidneys during treatment as well.
Written by Dr. Lindsay Taylor