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Hyperthyroidism is the most common endocrine system disorder in cats. It is seen most frequently in cats with an average age of 13 years. This condition is the result of an overactive thyroid gland which produces an excessive amount of the two thyroid hormones that regulate metabolism (T3 and T4). This can be caused most frequently by a benign tumor on one or both of the lobes of the gland.
There are several very effective methods of treatment available to cats and their owners today including: the administration of antithyroid drugs such as propylthiouracil (PTU) and methimazole (Tapazole); surgical removal of one or both of the enlarged thyroid lobes (thyroidectomy); and radioactive iodine treatment. Because this condition, when left untreated, can cause severe damage to a cat's metabolism and heart, early detection, as in most disease processes, is crucial.
What You Might Notice in a Cat with Hyperthyroidism
The onset of symptoms of hyperthyroidism can be slow and gradual, thus more difficult for the owner to detect until the disease has progressed. Because the metabolism has been accelerated, weight loss is quite common even though the cat displays a ravenous appetite. They may eat more frequently, more voraciously, and if allowed outdoors to hunt, you may notice an increased desire for fresh bird or mouse meat.
Occasionally the reverse will be presented with a cat acting weak and listless, almost dazed, with no appetite in evidence.
Excessive vomiting, diarrhea, drinking, and urinating are also commonly seen signs. The cat may seem hyperactive and nervous, and in many cats this is displayed as increased vocalization. You may suddenly feel as if your cat is screaming at you more often than usual, especially in the night and early morning hours.
The coat can look unkempt if the cat is undergrooming, but excessive grooming is also possible with resultant hair loss. Lesions on the skin can cause shedding of the fur and your cats claws may seem to grow faster and longer than normal. Heat intolerance is common since the cat's own internal thermostat has been revved up. You may notice them always looking for the coolest place in the house or yard to rest.
The heart is frequently affected with rapid heartbeat (tachycardia) common as well as murmurs and arrhythmias and more seriously, changes in the heart muscle itself. The cat may have difficulty breathing and an inability to tolerate exercise or stress. Hyperthyroidism takes its toll on the feline heart and while most of the heart damage is reversible, up to 15% of the cats affected will suffer congestive heart failure. Until the cat is stabilized, usually on antithyroid medication, anesthetic administration is very risky, again further reason to notice the waring signs and most common symptoms early on.
Because this condition can affect every organ and system in the feline body, early detection is critical. Several effective courses of treatment exist today. Determining the right course for your cat is a decision that can only be made after consultation with your veterinarian and a thorough battery of tests to determine the severity and progression of the disease.
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