Diagnosis & Treatment

Hyperthyroidism in Cats

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Hyperthyroidism is one of the most common endocrine disorders in cats and is caused by the overproduction of thyroid hormones (T4 and T3). It is mainly seen in middle-aged and older cats, usually over 7 years of age, and significantly affects their overall health and quality of life.
In the vast majority of cases (>95%), hyperthyroidism is due to benign adenomatous hyperplasia or adenomas of the thyroid gland. Malignant tumors (carcinomas) are rare and account for fewer than 2–3% of cases.

About the Thyroid Gland

The thyroid gland is located in the neck, on either side of the trachea. In the cat, it consists of two small lobes, which are normally not palpable.
The thyroid hormones Thyroxine (T4) and Triiodothyronine (T3) regulate the body’s metabolism, affecting vital organs such as the heart, kidneys, liver, nervous system, muscles and skin.

Clinical Signs

Increased production of thyroid hormones leads to accelerated metabolism, leading to symptoms such as:

  • Weight loss, despite increased or normal appetite
  • Hyperactivity, restlessness, nervousness
  • Polyuria – polydipsia
  • Increased heart rate or arrhythmias
  • Behavioral changes may include:
  • Irritability or aggression
  • Sleep disturbances
  • Muscle tremors
  • Increased sensitivity to stress
  • Other possible clinical signs:
  • Vomiting, diarrhea or increased bowel movements
  • Poor coat quality
  • Ocular lesions (mainly in the retina)

An Atypical form of hyperthyroidism occurs in 5–15% of cats, the clinical presentation is the opposite of typical hyperthyroidism, with lethargy, anorexia and overall weakness, which makes diagnosis difficult.

Diagnosis

Diagnosis is primarily based on measuring total thyroxine (T4) levels in the blood. The value is diagnostic in most cases. For a comprehensive evaluation of the patient, the following are also recommended:

  • Complete blood count (CBC)
  • Blood chemistry panel (liver – kidneys)
  • Urinalysis
  • Test for FeLV & FIV
  • Imaging test (ultrasound, x-rays), when deemed necessary

Hyperthyroidism & Chronic Kidney Disease

Hyperthyroidism often coexists with chronic kidney disease (CKD). The increased cardiac output caused by hyperthyroidism may mask underlying renal dysfunction.
For this reason, the therapeutic approach is individualized and requires close monitoring, so that treatment of the thyroid condition does not lead to deterioration of kidney function.

Treatment

Hyperthyroidism is a manageable and treatable disease, as long as it is diagnosed early and treated correctly. Regular preventive checkups in older cats are crucial. The most frequently chosen solution involves daily administration of antithyroid drugs. Regular monitoring is required, especially in the first few months. Possible side effects include anorexia, vomiting, or lethargy, usually within the first three months of treatment.

At PAWsitive Vet Care, we have the expertise and equipment needed to provide accurate diagnosis, individualized treatment, and long-term monitoring of your cat’s health.