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Symptoms of Hyperthyroidism in Cats

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Lindsay Butzer, DVM
Doctor of Veterinary Medicine

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Lindsay Butzer, DVM
Doctor of Veterinary Medicine

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Common symptoms of hyperthyroidism

Many cats with hyperthyroidism lose weight despite being ravenous. Often these cats eat so quickly that they vomit. Many also have diarrhea. They are hyperactive and irritable, expressing a meanness that hadn't been seen before. They look unkempt and have poor coats and thickened nails. Their hearts beat so strongly and rapidly that you can feel a "gallop" rhythm with your hand over the chest.

How is hyperthyroidism diagnosed?

Tests that suggest hyperthyroidism in cats

Blood tests: The blood may be slightly thick with more red blood cells than normal (erythrocytosis). The white cells may be elevated (leukocytosis), but two types of white blood cellsa-"lymphocytes and eosinophilsa-"will be low. This type of blood count is typical of a stress response. The liver enzyme, ALT, will be high in most pets. Some pets will also have high ALP, LDH, AST, BUN, creatinine, glucose, phosphorus and bilirubin as they experience complications from hyperthyroidism.
Thyroid tests: Thyroid hormones, especially free T4, is elevated. T3 may also be elevated.