[Written by a Veterinarian] Is your cat eating but still losing weight? It might be hyperthyroidism. Symptoms to check and treatment options.

"My senior cat has a great appetite and is very energetic lately!" Are you happy about this?

Actually, for older cats, "losing weight despite eating" is a classic sign of "hyperthyroidism." This time, we will explain hyperthyroidism, which is common in cats aged 7 and older, focusing on the signs you should not miss and the correct ways to deal with it.

Losing weight despite eating? What is feline hyperthyroidism?

Role of the Thyroid Gland

The thyroid gland is a tissue in the throat that secretes thyroid hormones necessary for a cat's survival. The main functions of thyroid hormones are as follows:

• Promotes energy production
• Regulates body temperature
• Enhances heart function
• Activates whole-body metabolism

Hyperthyroidism leads to an abnormally active metabolism throughout the body due to the excessive secretion of thyroid hormones. As a result, cats may lose weight despite eating, be unusually energetic for their age, or even experience a sudden change in personality, becoming aggressive.

Don't miss these early signs! Easy to mistake for "getting more energetic"

This disease is also known as "the happy disease" because, in its early stages, cats become more active, often leading owners to mistakenly believe their cat has "rejuvenated." However, this is a pathological condition, and if it progresses, it places a significant burden on the body. Check for the following signs:

• Abnormally increased appetite (starts stealing food), but does not gain weight or even loses weight: Due to muscle mass loss.
• Drinks a lot of water and urinates more frequently (polydipsia and polyuria): Due to increased renal blood flow, which increases urine production.
• Restlessness, pacing, vocalizing at night, or becoming aggressive: Due to increased metabolism making nerves overactive.
• Poor coat quality (dull and dry), hair loss: Due to hair metabolism.
• Thickened, overgrown claws: Due to accelerated nail growth.

Risk of life-threatening complications if left untreated

While thyroid hormones play a crucial role in maintaining life, excessive secretion can lead to abnormal metabolic acceleration and increased strain on the heart. Therefore, if left untreated, the cat remains in a state similar to constantly running at full speed, placing a significant burden on the heart and kidneys, which can lead to cardiomyopathy or hidden kidney failure (normal kidney function but in a state of kidney failure).

Why does it happen? Common causes in older cats and examination methods at the vet.

Causes and common age of hyperthyroidism

It is most common in elderly cats aged 12-13 years and older, but it is said that about 10% of cats aged 7 and older are affected. In the early stages, owners often do not notice the symptoms, and it is said to be more common in female cats during health check-ups or vaccinations. Hyperthyroidism can cause the thyroid gland to swell, but most of these are benign hyperplasia or adenomas, and thyroid cancer is rare in cats.

The cause of hyperthyroidism is unknown, but since thyroid hormones involve a substance called iodine, dietary iodine may be involved in its development. There are also reports suggesting the involvement of canned cat food (aluminum cans), and it is said that the risk is five times higher compared to cats that eat dry food.

Diagnosis methods

Palpation: The veterinarian feels the cat's throat to check for swelling (lumps) of the thyroid gland. However, a diagnosis cannot be made by palpation alone, as normal cats can also have enlarged thyroid glands.

Visual inspection: The veterinarian checks the cat's physique, muscle mass, coat condition, and nail condition. If the cat is too thin, overly energetic, has a scruffy coat, or thick nails, hyperthyroidism is suspected. If hypertension is present, eye bleeding or retinal detachment may occur.

Auscultation: If cardiomyopathy has developed, heart murmurs may be heard, or the heart rate may be rapid. If cardiomyopathy is advanced, respiratory abnormalities can occur, and lung sounds may be heard.

Blood tests: In addition to complete blood count and biochemical tests, blood levels of thyroid hormone (T4) are measured. However, in early-stage hyperthyroidism or if other diseases are present, the levels may be within the normal range. In such cases, free thyroid hormone (fT4) measurement is performed. These tests may not be available in-house.

Can it be cured? Three treatment methods including medication, diet, and surgery, and home care.

Hyperthyroidism is a condition that can be managed long-term with proper control. The following three treatment methods are mainly chosen based on the cat's personality and the owner's lifestyle.

1. Medical therapy (antithyroid drugs)

Giving medication daily to suppress the synthesis of thyroid hormones is the most common method. Although tablets are given, cat-specific medications are often formulated to mask bitterness, making them easier to administer. Medication must be continued for life.

Additionally, if there are co-occurring conditions (cardiomyopathy, high blood pressure, kidney disease), medication for those conditions will also be necessary.

2. Dietary therapy (prescription diet)

This method involves feeding a specialized prescription diet that restricts "iodine," a material for thyroid hormones.

In some cases, dietary therapy alone may be sufficient for management, but strict control is required, meaning "nothing else can be eaten." Therefore, whether the cat will eat the prescription diet is key.

*In multi-cat households, measures are needed to ensure other cats do not eat the prescription diet.

3. Surgery

This involves surgically removing the enlarged thyroid gland. The advantage of surgery is that if successful, there is a possibility of a cure, eliminating the need for frequent vet visits or medication. The disadvantage is the high anesthesia risk due to the common advanced age of affected cats. Additionally, if the parathyroid glands (which secrete hormones that regulate calcium) attached to the thyroid gland are removed, there is a risk of death due to hypocalcemia.

Not all veterinary hospitals can perform thyroidectomy, so surgery is recommended when maintenance with medication or dietary therapy is no longer sufficient.

Summary

"Losing weight despite eating" or "suddenly becoming active" might not be signs of aging, but rather hyperthyroidism. Early detection and control of hormone levels with medication or food can restore a peaceful daily life. If your beloved cat is over 7 years old, regularly check for changes in weight and appetite balance, and ensure regular health check-ups.