Reviewed by Dr. Fiona Lee
Hyperthyroidism is a common health problem in cats, particularly among cats age 10 and older.1 Learn the symptoms and signs to look out for so you can help ensure early detection and effective management to keep your kitty healthy and active.
What is hyperthyroidism in cats?
Hyperthyroidism stems from an overactive thyroid gland, which is a small butterfly-shaped organ located in a cat's neck. It can affect one or both thyroid glands and is usually from a benign swelling on the gland, with just 1% to 3% of cases due to a cancerous growth.2 The thyroid plays a crucial role in regulating the body's metabolism. When it becomes overactive, it produces excessive amounts of thyroid hormones, leading to a cascade of health issues in cats.
Causes of hyperthyroidism
While the exact causes are not always clear, certain risk factors contribute to the development of hyperthyroidism in cats. Genetic predisposition may make some cats more susceptible to the condition, but the most common factor is age, with most cases occurring in cats age 10 or older.1 As your cat could potentially live up to 20 years or longer, or at least to the average of between 13 and 14 years, providing good healthcare can help extend the life span of your cat so you can enjoy many more happy memories together.3
There have also been some reports linking fish-flavored canned food to hyperthyroidism in cats, although the evidence is not yet solid.4
Other possible contributing factors being debated by veterinarians include the potential risk from polyfluoroalkyl substances (PFAS), which are found in cleaning products; water-resistant fabrics such as rain jackets, umbrellas and tents; grease-resistant paper; nonstick cookware; and stain-resistant coatings used on carpets, upholstery and other fabrics.
Symptoms of hyperthyroidism in cats
Cats of all breeds and sizes can develop hyperthyroidism, although it's very rare in young cats. Some breeds, such as Abyssinian, British Shorthair, Burmese, Persian, Siamese and Tonkinese, may have a decreased incidence of hyperthyroidism compared to other breeds.1 Recognizing the symptoms of hyperthyroidism is essential for timely intervention. Cats with hyperthyroidism often exhibit a range of physical and behavioral changes.
Physical symptoms
- Weight loss despite increased appetite: One of the common clinical signs of hyperthyroidism is weight loss, even though the cat maintains an insatiable appetite.
- Increased thirst and urination: The overactive thyroid leads to increased thirst and urination, affecting the cat's overall hydration levels.
- Rapid breathing or difficulty breathing
- Increased heart rate
- An enlarged lump on the neck (thyroid gland)
Behavioral changes
- Irritability: Cats with hyperthyroidism may become irritable and easily agitated.
- Aggression: Behavioral changes can include increased aggression toward other pets or even humans.
- Changes in grooming habits: A cat's grooming habits may change, leading to an unkempt coat.
- Hyperactivity: Hyperthyroidism can cause an increase in overall activity levels, making a once sedate cat suddenly more energetic and restless.
Diagnosing hyperthyroidism
Hyperthyroidism won't go away by itself. In fact, it will progress with worsening symptoms. These can include severe weight loss and secondary conditions like serious heart problems and high blood pressure, which can damage your cat's eyes, kidneys, heart and brain. However, once the right treatment plan is started, many of these conditions and symptoms can be reversed.5
Veterinary examinations are crucial for diagnosing hyperthyroidism in cats. These involve a thorough physical exam, blood tests to measure thyroid hormone levels and sometimes imaging techniques such as ultrasound to visualize the thyroid gland's condition if a malignant tumor is suspected.
Treating hyperthyroidism in cats
Effective treatment options exist for feline hyperthyroidism, each with considerations that you should discuss with your veterinarian.
Medication
Antithyroid drugs such as methimazole (Tapazole®; Felimazole®) are commonly prescribed to control hyperthyroidism. While effective, pet owners should be aware of possible side effects, including depression, vomiting and lack of appetite. Other signs may include facial excoriation (a type of allergy to the medication) and, in rare cases, bone marrow suppression.
Radioactive iodine therapy
Considered the gold standard for treatment, this therapy involves injecting radioactive iodine under the cat's skin or intravenously. It selectively targets and destroys the overactive thyroid tissue, providing a curative solution. Though there are potential side effects, such as temporary hypothyroidism, the overall success rates make it a preferred choice.
Surgical intervention
Surgery, specifically thyroidectomy (removing one or both thyroid lobes), is a less common option due to its invasiveness and potential complications. It may require a second surgery if the remaining thyroid becomes hyperactive or if ectopic thyroid tissue exists.
Lifestyle changes and supportive care
Dietary considerations, including specialized diets with limited iodine, can be part of the treatment plan. Regular monitoring through veterinary checkups ensures adjustments to the treatment as needed for optimal results. Find a veterinarian in your area with our handy map.
How to manage hyperthyroidism in cats
Detecting and managing hyperthyroidism involves proactive measures, including:
- Regular veterinary checkups. Early detection through routine checkups allows for prompt intervention and improved outcomes.
- Monitoring older cats. Keep a close eye on older cats for potential risk factors, such as changes in behavior or weight loss. With annual blood work, your veterinarian can monitor trends in their thyroid hormone over time, especially in relation to any weight lost.
Keep your cat feeling healthy by providing a balanced diet to maintain an ideal weight. You can always check with your veterinarian to find the best diets to feed your cats.
As with all pets' medical conditions and complaints, it's important to remain vigilant to any new symptoms or changes in your cat's behavior to allow for early recognition and treatment for hyperthyroidism.
Pets Best is here to help
Despite the challenges, the prognosis for hyperthyroidism in cats is generally positive. And with the right care, many cats can lead happy and healthy lives as seniors. Seeking prompt veterinary attention is crucial, which is why having a comprehensive pet insurance policy can be an advantage. Pets Best policies don't have an age limit, so you can help keep your kitty healthy well into their sunset years. Explore Pets Best cat insurance options and take advantage of the 24/7 Pet Helpline for expert advice at any time of day or night.
Sources/Citations
- “Hyperthyroidism in Cats," Malcolm Weir et al., VCA Animal Hospitals, https://vcahospitals.com/know-your-pet/hyperthyroidism-in-cats, accessed December 28, 2023.
- “Hyperthyroidism in cats," (11/2018), The People's Dispensary for Sick Animals, https://www.pdsa.org.uk/pet-help-and-advice/pet-health-hub/conditions/hyperthyroidism-in-cats, accessed December 28, 2023.
- “What age? What stage?" (1/2019), International Cat Care, https://www.catcare4life.org/cat-owners/lifestages/, accessed December 28, 2023.
- “Hyperthyroidism in Cats: Symptoms and Treatment," Lorie Huston (3/2020), PetMD, https://www.petmd.com/cat/conditions/endocrine/c_ct_hyperthyroidism, accessed December 28, 2023.
- “Symptoms," (3/2017), Hyperthyroid Cat Centre, https://www.hyperthyroidcatcentre.co.uk/cat-owners/about-hyperthyroidism/symptoms/, accessed December 28, 2023.