Hyperthyroidism is one of the most commonly diagnosed conditions in older cats, and it can creep up so gradually that even doting pet parents may miss the early warning signs.
Because thyroid hormones control metabolism, small changes in the thyroid gland can have big impacts on your cat’s overall health. The sooner hyperthyroidism is identified, the easier it is to manage, and the better your cat’s long-term outcomes tend to be.
Whether your cat has recently started exhibiting worrisome behavioral changes or you’re simply trying to stay ahead of age-related illness, learning to spot the subtle signs of hyperthyroidism can make a meaningful difference in your cat’s quality of life.
What is Feline Hyperthyroidism?
Located in the neck, the thyroid gland produces hormones that regulate metabolism, energy use, and organ function. As cats get older, the cells in this gland can sometimes become overactive and release an excess of thyroid hormones — a condition known as hyperthyroidism.
About 97% of cases are caused by a benign overgrowth of thyroid tissue (called a thyroid adenoma), though thyroid tumors are occasionally cancerous. In either case, the overproduction of thyroid hormones speeds up the metabolism, which forces every system in the body to work harder than it normally would.
Onset is subtle and the effects are cumulative, but if left unaddressed, hyperthyroidism will strain your cat’s organs and shorten their life.
Risk Factors for Thyroid Disease in Cats
Age is the biggest predictor of an overactive thyroid. Hyperthyroidism is rare in young cats and most common after age 10.
Researchers are still exploring other risk factors for thyroid illness, with some evidence pointing to a possible genetic component (Siamese and Burmese cats appear slightly less prone).
While this disease is still being studied, annual senior wellness exams are the best tool currently available for early detection.
Signs of an Overactive Thyroid Pet Parents May Miss
Many people associate hyperthyroidism with dramatic weight loss or constant hunger, but the earliest changes are usually more nuanced. If your cat is entering their golden years (age 10 and up), here are the small but telling signs to watch for.
Changes in Daily Habits
As a pet parent, you have a good sense of what normal behavior looks like for your feline friend. Pay close attention to changes like:
- Pacing or restlessness
- Irritability
- Excessive vocalizing
- Seemingly random bursts of energy
- Eating more frequently or gobbling food
- Increased thirst or more frequent litter box trips
It’s easy to dismiss these changes as “senior cat behavior,” so don’t ignore your instincts if something seems off.
Changes Body Condition
Hyperthyroidism causes a depletion of body fat and muscle tissue, but early weight changes are often quite minor. A loss of a few ounces each month can be hard to notice, especially for long-haired, “fluffy” cats.
If you’re concerned about your cat’s thyroid health, it’s a good idea to track their weight. A steady decline, even if it’s small, warrants a visit to the vet.
Changes in Your Cat’s Coat
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Don’t ignore changes in your cat’s appearance or grooming behavior. Cats with hyperthyroidism can sometimes have:
- Unkempt, greasy, or matted fur
- Increased shedding
- A dull coat despite eating well
Changes in Digestive Health
A sped-up metabolism can affect the way your cat’s body processes food.
Increased feelings of hunger may lead to rushed eating, which then results in vomiting. On the other hand, faster digestion reduces the amount of time that food spends in your cat’s gastrointestinal tract, leading to more voluminous and frequent stools.
These symptoms are easily mistaken for dietary sensitivity or hairballs, but they can be early indicators of an overactive thyroid.
Why Early Detection Matters
Hyperthyroidism doesn’t just speed up metabolism — it places strain on vital organs. Left untreated, the condition can lead to:
Heart Problems
Excess thyroid hormones force the heart to work harder, often causing:
- High blood pressure
- Rapid heart rate
- Heart murmurs
- Thickening of the heart muscle
These changes can progress to congestive heart failure if not addressed.
Undiagnosed Kidney Problems
Thyroid disease can “mask” underlying kidney problems by artificially increasing blood flow. This can make kidney dysfunction harder to catch until it has progressed significantly.
Digestive Issues and Liver Disease
The metabolic changes caused by hyperthyroidism make it difficult for cats to absorb nutrients from food, leading to muscle loss that is hard to reverse in senior cats.
They may also experience chronically elevated liver enzymes, which can contribute to fatty liver disease over time.
In short, an early diagnosis is essential to protect your cat’s body systems as they age.
Treatment Options to Help Cats Thrive
Fortunately, hyperthyroidism is highly treatable — the biggest obstacle is recognizing the signs and taking action.
Once your vet confirms an overactive thyroid through bloodwork, you’ll be able to explore your options for managing or reversing thyroid disease.
Medication that blocks excessive thyroid hormone production is the most common treatment, though in some cases, your vet may recommend radiation or surgery. Regular wellness exams are especially important for cats with hyperthyroidism to confirm that treatment is working and your pet’s metabolic health is improving.
Hyperthyroidism is common, but with early detection and proper care, most cats live long, comfortable, and happy lives. If your cat is entering their senior years or you’ve noticed subtle changes in their health or habits, don’t wait to reach out to your veterinarian.
Early intervention is key to reducing the strain on your cat’s organs and preventing irreversible damage.