Wouldn’t it be wonderful to eat whatever you wanted and still lose weight? While many people beyond college-age dream about that, this phenomenon can be a sign of hyperthyroidism, a serious endocrine disease and the most common glandular disorder in cats. Hyperthyroidism is routinely diagnosed in middle-aged to older cats so, if you have an older feline companion, you should brush up on your hyperthyroidism knowledge to be able to quickly spot the signs, and get your cat prompt treatment. Check out Dr. Man’s video blog for a quick run-down on feline hyperthyroidism, or read further for a more in-depth look. 

What is feline hyperthyroidism?

Hyperthyroidism occurs when the thyroid gland makes and secretes high levels of the thyroid hormone thyroxine. The typical cause is a benign tumor in the thyroid gland, but hyperthyroidism can also be caused by abnormal glandular changes. 

What function does the thyroid gland serve in cats?

The thyroid gland is located in your cat’s neck and is divided into two lobes, one on either side of the trachea (i.e., windpipe), right below the larynx (i.e., voicebox). You cannot feel normal thyroid glands in cats, but the abnormalities or tumor development associated with hyperthyroidism can cause an enlarged gland. 

The thyroxine that the thyroid gland produces is essential for normal skeletal and brain growth in kittens. In adult cats, the hormone is involved in the following functions:

  • Metabolism regulation
  • Body temperature control
  • Weight gain and loss
  • Heart rate and cardiac output
  • Nervous system function
  • Reproduction
  • Muscle development
  • Skin health
  • Red blood cell production

How common is hyperthyroidism in cats?

Hyperthyroidism affects up to 10% of older cats. While no genetic predisposition for hyperthyroidism is known in cats, Siamese and Himalayans are thought to have a decreased risk. Otherwise, this disease affects male and female cats equally, most commonly appearing in middle-aged to older cats. Hyperthyroidism is extremely rare in young cats, and seldom appears before age 4. 

Some theories about the cause of hyperthyroidism in cats include:

  • Thyroid cancer
  • Some fish-flavored canned food diets
  • Flame-retardant chemicals used in some furniture and carpeting, and circulated in house dust
  • Advancing age 

What will I see if my cat has hyperthyroidism?

Hyperthyroidism is a progressive disease with a slow, subtle onset. Early signs may be hard for pet owners to recognize, as a poor hair coat and body condition are generally chalked up to old age. Additionally, not all hyperthyroid cats demonstrate the classic signs, and may instead show a lack of appetite and weakness. However, the most common hyperthyroidism signs in your cat may include:

  • Weight loss
  • Greatly increased appetite
  • Unkempt appearance
  • Poor body condition
  • Vomiting
  • Diarrhea
  • Excessive thirst
  • Excessive urination
  • Difficult or rapid breathing
  • Heart murmur
  • Rapid heart rate or murmur (i.e., gallop rhythm)
  • Hyperactivity or restlessness
  • Aggression
  • Enlarged thyroid gland
  • Thickened nails

Other endocrine disorders, such as diabetes, can present similarly, so a thorough physical exam and diagnostic workup is essential for determining the cause of your cat’s excessive thirst, urination, and hunger. 

How is hyperthyroidism in cats diagnosed?

Hyperthyroidism in cats is best diagnosed through a thorough physical exam, history, and laboratory testing. If your cat displays any hyperthyroidism signs, Dr. Man will recommend testing their thyroxine level by taking a blood sample to measure the circulating thyroid hormone level in the bloodstream. We will also check your cat for other conditions common in older cats, such as kidney disease and heart issues, as concurrent diseases can influence and complicate hyperthyroidism treatment.

How is hyperthyroidism in cats treated?

Hyperthyroidism in cats is usually manageable with treatment that reduces the level and the effects of excessive thyroid hormone. Treatment options include:

  • Medical — Medical treatment is used for lifelong pharmaceutical hyperthyroidism management, or prior to iodine treatment or surgery. Medications that block thyroid hormone manufacture can be used to return levels to normal.
  • Radioactive iodine — Radioactive iodine treatment is the gold standard treatment for feline hyperthyroidism. This therapy requires specialized facilities and hospitalization until the radioactive material leaves your cat’s body, but most cats are cured with a single treatment. 
  • Surgical — Surgical thyroidectomy involves removing one or both lobes of the thyroid gland to eradicate the diseased tissue. Cats usually undergo two to four weeks of medical treatment to improve their condition and minimize potential anesthetic and surgical risks. Surgery is curative in many cases, although hyperthyroidism does recur in up to one-third of cases because of disease in the other thyroid gland, or ectopic tissue. Removing both thyroid glands can result in hypothyroidism, which requires lifelong treatment.
  • Diet — Iodine is necessary for a properly functioning thyroid gland and hormone production, so restricting dietary iodine may help cats manage hyperthyroidism, as long as this diet type is fed exclusively.

Although hyperthyroidism is fatal if left untreated, many treatment options are available if your cat is diagnosed with this endocrine disorder. 

Have you noticed your cat losing weight, despite a ravenous appetite? Or, maybe your pet is drinking and urinating excessively? To get to the bottom of your cat’s illness, contact your Boca Midtowne Animal Hospital team.