The thyroid glands, located in your cat’s neck, control your cat’s metabolic rate by producing the the thyroid hormones T4 and T3. Hyperthyroidism occurs when excessive amounts of T4 and T3 are produced by a cancerous growth in the thyroid. The tumour tissue most often occurs in both glands at the same time. The excessive levels of thyroxine can be damaging to many body systems including the heart and kidneys. Because this is a cancerous process the disease will never go into remission. Treatment requires curing the disease with radioiodine therapy or surgery or treatment with lifelong daily anti-thyroid drugs..

Hyperthyroidism is the most common endocrine disease of cats and is increasing in incidence. It is estimated that up to 10% of senior cats will develop hyperthyroidism.

The most common signs of hyperthyroidism are weight loss, muscle mass loss, increased appetite, vomiting, increased thirst, increased activity, shedding or hair coat changes, vocalization, agitation, and panting. On physical exam your veterinarian may notice a heart murmur or irregular rhythm from damage to the heart, or an enlarged thyroid nodule. Hyperthyroidism is most often diagnosed by an elevated T4 level in a blood sample, but can also be diagnosed with a free T4, unmeasurable TSH level or nuclear medicine scan.

The average age at diagnosis is 12 years but we also see this disease in much younger cats. Both males and females get hyperthyroidism equally.

Radioiodine therapy is the gold standard for the treatment of hyperthyroid cats, just as in humans with the same disease.