Hyperthyroidism, a condition affecting older cats (usually over 7 years old), is caused by an overproduction of thyroid hormone. While thyroid hormone is essential for various bodily functions, including growth, fur production, and activity levels, its primary impact on senior cats is on their metabolism.

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What's the Cause?

In most cases, hyperthyroidism results from a benign change in one or more thyroid glands, known as "hyperplasia" or "adenoma." This causes the gland to enlarge and produce excessive thyroid hormone. While no single cause has been identified, it appears more common in indoor cats and those who consume canned food.

A smaller percentage of cases (< 5%) are caused by a malignant thyroid cancer called thyroid carcinoma.

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Recognizing the Signs

Hyperthyroidism in cats presents with a range of signs, but the most common include:

• Increased Appetite: Despite eating more, cats with hyperthyroidism often lose weight.
• Increased Drinking: They may drink excessively, sometimes even to the point of becoming incontinent.
• Weight Loss: This is a hallmark symptom, despite a hearty appetite.
• Hyperactivity: Affected cats often display increased energy levels and restlessness.
• Aggression: Some hyperthyroid cats become more irritable and aggressive.
• Lethargy: Surprisingly, some cats exhibit the opposite, becoming quiet and sluggish.
• Vomiting and Diarrhea: These symptoms can be frequent and persistent.

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Your vet may feel for an enlarged thyroid gland during an examination, a sign known as a "goiter." Hyperthyroid cats also tend to have a rapid heart rate and sometimes exhibit dangerously elevated blood pressure.

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Diagnosis and Treatment

A simple blood test is usually enough to diagnose hyperthyroidism. Elevated thyroid hormone levels confirm the diagnosis.

However, diagnosis can be challenging as other illnesses can also affect thyroid hormone levels. Further blood tests and imaging (ultrasound or scintigraphy) might be necessary for a definitive diagnosis, especially when thyroid levels are in the mid-to-high end of the normal range.

Many treatment options are available for hyperthyroidism. Most cases start with oral medication (tablets or liquids) to suppress thyroid hormone production. While this manages the disease, it's not a cure, and treatment is required for life.

More permanent solutions include:

• Thyroidectomy: Surgical removal of the thyroid gland.
• Radioactive Iodine Treatment: This targets the thyroid tissue, destroying it without affecting other tissues. It's a specialized procedure requiring hospitalization.
• Ultra-low Iodine Diets: These diets restrict iodine intake, preventing thyroid hormone production. However, they are challenging to implement and the effectiveness can vary.
• Trans-dermal Gels: These gels contain medication absorbed through the skin, but their effectiveness is variable and accurate dosing is difficult.

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Potential Side Effects and Complications

A common side effect of hyperthyroidism treatment is the "unmasking" of pre-existing kidney disease. Since kidney disease is prevalent in older cats, it can be hidden by hyperthyroidism. Treatment for hyperthyroidism can reveal the condition, requiring careful management to balance both conditions.

Treatment can also lead to the opposite problem: hypothyroidism (low thyroid levels). This can cause lethargy, decreased appetite, and can also lead to kidney issues. Some cats who have undergone curative treatment may require ongoing thyroid hormone supplementation.

As with any medication, side effects are possible. The most common are vomiting and reduced appetite. Less frequent side effects can include skin problems and facial itching.

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Long-term Consequences

Untreated hyperthyroidism can have serious consequences, including:

• Hyperthyroidism-associated Heart Disease: Due to the persistently high heart rate, the heart can be affected.
• High Blood Pressure: Elevated blood pressure can damage kidneys, eyes, brain, and heart, requiring additional medication.

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Prognosis for Cats with Hyperthyroidism

With proper management, cats with hyperthyroidism can live long and healthy lives with a good quality of life. However, without treatment, the disease could lead to severe weight loss, heart disease, and ultimately death.

If you suspect your cat may have hyperthyroidism, schedule a visit with your veterinarian for a diagnosis and treatment plan. Early intervention is crucial for the well-being of your feline friend.