While cats and dogs occupy similar spaces in our homes and hearts, they are different species whose bodies function to their species’ needs. Cats and dogs also develop different conditions and disease types. One example in which these species greatly differ is the manner in which they experience thyroid disease. While both species are prone to thyroid problems as they age, cats’ and dogs’ specific thyroid diseases and signs are opposite one another. To help you better understand this common condition, our Palm Valley Veterinary Center team answers your frequently asked questions about thyroid disease in pets.

Question: What are the most common thyroid diseases in pets?

Answer: High thyroid levels (i.e., hyperthyroidism) and low thyroid levels (i.e., hypothyroidism) are the most common thyroid diseases in pets. These changes typically develop in middle to older age, and are caused by gland destruction, gland inflammation, or benign tumors. Malignant (i.e., cancerous) thyroid tumors are uncommon in pets.

Q: How does thyroid disease differ in cats and dogs?

A: Cats nearly always develop hyperthyroidism, while dogs typically develop hypothyroidism. The opposite is rarely true, but can theoretically occur under specific circumstances. Because cats and dogs develop opposite disease types, their signs are also on opposite ends of the spectrum. 

Hyperthyroidism speeds up a cat’s metabolism, which can make them feel anxious, hyperactive, and hungry. Long-term or uncontrolled hyperthyroidism can cause heart disease and/or high blood pressure, which damages a cat’s retinas, leading to blindness. Thyroid disease signs in cats include:

  • Weight loss
  • Chronic diarrhea
  • Ravenous appetite
  • Anxiety or restlessness
  • Rapid heart rate
  • High blood pressure
  • Heart disease or failure
  • Blindness

Hypothyroidism slows a dog’s metabolism, which makes them feel sluggish and can negatively impact their immune function, resulting in chronic infections. Thyroid disease signs in dogs include:

  • Weight gain
  • Poor appetite
  • Low energy
  • Heat-seeking behavior
  • Slow heart rate
  • Skin infections
  • Hair loss
  • Behavior disorders
  • Seizures—in severe cases

Q: How is thyroid disease diagnosed in pets?

A: A simple blood test can diagnose or increase suspicion for thyroid disease in pets. If the initial blood test is normal or borderline, but your pet’s signs suggest a thyroid problem, our veterinarian can perform additional tests to confirm or rule out the disease. Early stage thyroid disease is more difficult to diagnose, and may require repeat testing after a few months.

Q: Can thyroid disease be cured?

A: Dogs who have hypothyroidism cannot be cured, as gland destruction or degeneration most often causes their disease. Damage to the thyroid gland cannot be reversed, but our veterinarian can treat and manage your pet’s signs with medications. Cats who have hyperthyroidism can be cured of their disease and return to normal thyroid function, but if they experience secondary heart or eye problems, the damage is likely permanent. 

Q: How is hyperthyroidism managed in cats?

A: Disease management strategies for cats focus on lowering thyroid levels to the normal range, and addressing secondary health issues such as high blood pressure or heart disease. Your cat’s treatment options depend on your preference, financial situation, and your feline friend’s overall health. Hyperthyroidism treatment options include:

  • Radioactive iodine — The thyroid gland uses iodine to make its hormones, so injecting a cat with radioactive iodine damages the gland without hurting their other body systems. To avoid exposing other pets or people to radiation, cats must be hospitalized and isolated for a few days after receiving the injection. 
  • Iodine-deficient diet — Depriving the thyroid gland of dietary iodine can also be an effective treatment. This option means feeding your cat a prescription diet, giving them no treats or other foods, including insects, rodents, or grass.
  • Daily medication — Methimazole can suppress thyroid hormone production, but you must give this to your cat twice daily for the remainder of their life. Administering daily medication can be a challenge, depending on your cat’s temperament. Methimazole can cause your cat side effects, however, few cats experience them.

Q: How is hypothyroidism managed in dogs?

A: Disease management strategies for dogs are considerably easier than for cats. Most dogs respond well to twice daily synthetic thyroid hormones to supplement their levels. The medication is inexpensive, and most dogs willingly swallow the small pills. Skin disease or chronic infections can linger. However, these signs are easily managed with medications until a dog’s overall condition improves.

Q: What will my pet’s veterinary care involve ?

A: All pets with thyroid disease require frequent monitoring to ensure their current treatments are working effectively, and that their thyroid hormone levels are not too high or too low. Our veterinarian will perform a blood test a few weeks after changing your pet’s medication, and once or twice per year for pets whose disease signs are stable. Hypothyroid dogs can live full, normal lives with appropriate treatment. Hyperthyroid cats who receive treatment early in the disease process can do well, but those who have severe or long-standing disease may have a shortened lifespan.

Thyroid changes often develop slowly over time, but signs aren’t always noticeable until the disease is in its later stage. Annual wellness examinations that include blood and urine tests are the best way to diagnose thyroid problems in the disease’s early stage. If your pet is showing thyroid disease signs or other health changes, or is due for a wellness visit, schedule an appointment with our Palm Valley Veterinary Center team.