Living with Hyperthyroidism

Hyperthyriodism is a clinical condition characterized by the overproduction of thyroid hormones produced by the thyroid gland. The thyroid gland is located in the neck and regulates metabolism, body temperature, blood pressure, heart rate and bowel function. Hyperthyroidism is normally caused by a benign thyroid tumor. Less than 2% are malignant. This is a fairly common disease of middle-aged cats. Hyperthyroidism can have serious, sometimes fatal affects if left untreated.

Clinical signs vary depending on the severity and how long the cat has been ill. The clinical signs are secondary to the increased metabolic rate and consist of:

  •     Weight loss despite good appetite
  •     Excessive appetite
  •     Vomiting and/or diarrhea
  •     Decreased grooming
  •     Irritability/hyperactivity and increased vocalization
  •     Excessive drinking and urination
  •     Panting, weakness, lethargy
  •     Heat avoidance

Associate conditions and disorders

The increase in the thyroid hormones leads to an increase in metabolic rate. The increased metabolic rate leads to increased pumping by the heart leading to hypertension. The heart must also enlarge and thicken to compensate for the increased metabolic demands leading to an abnormal gallop murmur and possibly blood clots. Hyperthyroidism and associated hypertension can also mask an underlying kidney disease. For this reason patient rechecks are very important after a treatment regiment is started

Treatments Options:

Medical treatment: Methimazole is an anti-thyroid medication that does not destroy the abnormal thyroid tissue but suppresses the production of thyroid hormone. Therefore the drug must be given for the rest of the cat’s life. Potential side effects include anorexia/vomiting, lethargy, and pruritus of the head and neck.

Thyroidectomy: Is the surgical removal of abnormal thyroid tissue. Medical treatment is recommended for several weeks before to unmask any underlying kidney disease, and improve metabolic and cardiac status. Postoperative complications include loss of parathyroid, Horner’s syndrome, and laryngeal paralysis.

Radioactive Iodine Therapy: An intravenous injection that concentrates in the thyroid rendering all abnormal tissue nonfunctional. After hospitalization no other treatment is required.

Science Diet Y/d: Limits dietary iodine intake reducing thyroid hormone production. The food is available in dry and wet. Must be the only diet offered. Y/D diet can be safely feed to non-hyperthyroid cats in a multi-cat home.


Recommended monitoring:

Exam, CBC, Chem 6, TT4, urinalysis at 2 weeks, then every 6 months.

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