Hyperthyroidism is a clinical syndrome due to excess thyroid
hormone and its clinical consequences. It is the most common endocrine disease of
middle-aged and older domestic cats. A silent killer, it relentlessly takes its toll
on body organs.
What are the Symptoms and Signs of this Disease?
The clinical manifestations of the disease are multisystemic
and relate to increased metabolic rate. Owners often overlook early symptoms
or assume the changes are a normal part of the aging process. Obvious
weight loss is usually the problem that takes the cat to their veterinarian.
Other signs include tachycardia (rapid heart rate), muscle weakness, goiter,
tachyarrhythmia (irregular heart rhythm), hyperexcitability, polyphagia
(increased appetite), heat intolerance, increased frequency of bowel movements,
polydipsia (increased thirst), polyuria (increased urination), vomiting,
and an unkempt hair coat.
Left untreated, cardiac disease progresses to heart
failure, hypertrophic cardiomyopathy and eventually leads to death. A
few patients may be surprisingly asymptomatic despite severe chemical
hyperthyroidism, particularly in the early stages of the disease (apathetic
What Causes Feline Hyperthyroidism?
Most cases are caused by adenomatous hyperplasia of
the thyroid gland. A benign adenoma (tumor) develops in the thyroid gland.
This change in the gland probably has a nutritional, environmental, or
genetic etiology which is still unknown. The result is uncontrolled production
of thyroid hormones, L-thyroxine (T4) and triiodothyronine (T3). In healthy
cats, the amount of thyroid hormone in the blood is regulated by the pituitary
gland through a negative feedback mechanism involving thytrotropin (TSH).
But in hyperthyroid cats, this normal endocrine regulation
goes awry, and the gland continually pours large amounts of thyroid hormones
into the blood. The resultant condition is hyperthyroxinemia and life-threatening
If you have questions regarding the treatment of Feline
Hyperthyroidism and how we can help your cat, visit the contacts
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