Thyroid Disease in Cats and Dogs
Dr. Megan Stewart of TVV Buckhead reports . . .
Both dogs and cats can develop thyroid disease, although it presents differently in each species. Hypothyroidism is usually diagnosed in dogs - while hyperthyroidism is most commonly diagnosed in cats. Hypothyroidism means that the thyroid gland is underactive while hyperthyroidism means that the thyroid gland is overactive. The thyroid gland in general is responsible for regulating the body’s metabolism. Thyroid disease can usually be diagnosed by a blood test performed by your veterinarian.
Hypothyroidism usually occurs in middle-aged to older dogs and large breed dogs are more likely to develop this disease. Certain breeds such as Golden Retriever and Doberman Pinschers are pre-disposed. Usually hypothyroid dogs present with lethargy, weight gain/obesity, or mental dullness. These signs can be subtle and may be attributed to part of the aging process. Skin issues are also common with hypothyroidism and may present as: thickened skin, hair loss, dry/brittle haircoat, and ear infections. Once hypothyroidism has been diagnosed by your veterinarian, a supplement is usually started. Most commonly levothyroxine sodium is used and is often needed for the pet’s lifetime. With thyroid supplementation, the dog may return to a normal activity level and skin issues may improve. Your veterinarian will likely recheck the thyroid level a few weeks after initiating therapy to ensure that the dosing is appropriate. (It is best to collect the blood sample four to six hours after a dose is given.)
Hyperthyroidism in cats is generally a disease of older cats and tends to be more serious than hypothyroidism in dogs. Over ninety percent of cats diagnosed with hyperthyroidism are eight years of age or older. Usually they present with weight loss despite a voracious appetite, hyperactivity (attitude changes, more vocal or restless, less grooming), and vomiting and/or diarrhea. Occasionally they can be lethargic and have a poor appetite. Treatment for hyperthyroid cats usually involves a medication called Methimazole. Your veterinarian will likely recheck bloodwork a few weeks after initiating therapy to ensure that the dose is appropriate. Because hyperthyroidism can mask kidney disease, it is best to monitor kidney values as well after starting therapy. Hyperthyroidism can also cause heart disease so once a cat is diagnosed, it is best to try and regulate the disease to help prevent progression of the heart disease. Some cats can live several years after being diagnosed with hyperthyroidism once regulated using Methimazole.
There are other options available for treatment of hyperthyroidism if medical treatment is not practical. For younger or stable cats (with no kidney disease) irradiation with I131 is an option. This basically kills abnormal thyroid cells while sparing normal cells. The drawback is that it can be very expensive (must be performed at a specialty hospital) and requires the cat to be hospitalized and isolated during the irradiation; however, if successful it is curative. Surgery is also a treatment option but because it is invasive, and there are medical options available, it is rarely performed. Since irradiation is not always a good option and because medicating cats daily is not always feasible, Hill’s Nutrition has developed a new prescription diet (Hill’s y/d) aimed to help treat hyperthyroidism. This diet restricts iodine absorption (which is needed for thyroid hormone production) therefore limiting the body’s ability to overproduce thyroid hormone and managing hyperthyroidism by diet rather than medication.
If you have any questions regarding your pet’s health or treatment options, please do not hesitate to call your veterinarian. This article is meant as a summary only.