What is Hyperthyroidism?

Has your older cat become unusually active? Is it losing weight despite increased appetite? Does it seek cooler areas and drink or urinate more frequently? These symptoms typically indicate hyperthyroidism, a condition caused by excessive thyroid hormone production. This imbalance accelerates metabolism, causing these signs. Some cats may instead show opposite symptoms, such as reduced appetite and low energy.

Consequences of Hyperthyroidism in Cats

Hyperthyroidism affects multiple organs, including the heart, blood pressure, gastrointestinal system, and kidneys:

• Heart: Thickening of heart walls, increased heart rate, heart murmurs, and potential heart failure.
• Blood Pressure: Hypertension, leading to eye abnormalities or even blindness.
• Liver: Potential reversible liver damage.
• Kidneys: Kidney disease often masked by hyperthyroidism can become apparent post-treatment.

Diagnosis

A physical exam can reveal enlarged thyroid glands and heart abnormalities. Blood tests measuring thyroid hormones confirm hyperthyroidism. Additional tests might be necessary to detect possible heart, liver, or kidney complications.

Treatments for Hyperthyroidism in Cats

Four therapeutic options exist, two of which are curative:

1. Medication (Methimazole)

• Administered orally (tablets, transdermal gel, or liquid).
• Blocks thyroid hormone production but doesn’t cure the disease.
• Regular monitoring (blood tests) required for dosage adjustments.
• Possible side effects: lethargy, appetite loss, vomiting, liver problems (rare).

2. Thyroid Surgery

• Removal of enlarged thyroid lobes.
• Potential cure but recurrence risk if abnormal cells remain.
• Possible complications: hypothyroidism, hypocalcemia (low calcium), anesthetic risks.

3. Radioactive Iodine Therapy

• Subcutaneous injection of radioactive iodine selectively destroying overactive thyroid cells.
• Usually curative with a single injection.
• 7-10 days hospitalization required (cat remains radioactive).
• Small risk of temporary hypothyroidism.

4. Prescription Diet (Hill’s y/d)

• Low-iodine diet helps restore thyroid function by reducing hormone production.
• Not recommended for non-hyperthyroid cats, posing challenges in multi-cat households.
• Effective for mild cases but challenging in moderate-to-severe conditions.

Monitoring and Prognosis

• Initial treatment: Methimazole often stabilizes cats before surgery or radioactive iodine therapy.
• Medical monitoring: Regular blood tests essential for treatment adjustments and detecting complications.
• Prognosis: Favorable if diagnosed early and treated appropriately.

If you suspect your cat has hyperthyroidism, consult your veterinarian promptly for diagnosis and management.