About Hypothyroidism in Cats

Hypothyroidism in cats occurs when the thyroid gland does not produce enough thyroid hormone to maintain normal metabolism. While common in dogs, hypothyroidism is a rare problem in cats, who are more likely to be hyperthyroid. If you suspect that your cat has this rare problem, you should talk to your veterinarian about testing and treatment.

Diagnosing Hypothyroidism in Cats

Hypothyroidism occurs because the thyroid gland cannot produce sufficient hormones or because the pituitary gland is not regulating thyroid hormone release correctly. Signs of hypothyroidism in cats include extreme lethargy, decreased appetite, constipation and dry, flaky skin. These signs, however, are not specific to hypothyroidism, so your veterinarian will not be able to diagnose your cat as hypothyroid without a thorough physical exam and further testing, including blood work, to rule out other potential causes of your cat's signs. In the absence of other causes, the veterinarian will use a blood test for T4 and/or free T4 to diagnose feline hypothyroidism.

Treating Hypothyroidism in Cats

The treatment for hypothyroid cats is supplementation with L-thyroxine (sodium levothyroxine), an oral thyroid hormone. Because thyroid hormone levels can vary in different  brands of this medication, it is important not change to a different generic brand without consulting a veterinarian. Periodically, treated cats need to have their hormone levels checked with a blood test that measures T4 and/ or free T4 levels. In addition, owners need to carefully monitor treated cats for signs of hyperthyroidism that indicate that the dose of medication is too high. These signs include excessive weight loss, ravenous appetite, vomiting, diarrhea, hair loss, heat intolerance, panting, sudden blindness and hyperactivity.  If you notice any of these signs, you should call your veterinarian right away to schedule your cat for a blood test to check his or her thyroid hormone levels.