Hyperthyroidism is a disease of middle-aged and senior cats caused by enlargement of the thyroid gland and subsequent increase in the release of thyroid hormones. Usually this enlargement is due to a benign tumor (non-cancerous) but rarely in can be a malignant tumor called adenocarcinoma. The release of excess thyroid hormones causes many problems including thickening of the heart wall and high blood pressure (hypertension). Thickening of the heart wall (also called hypertrophic cardiomyopathy or HCM,) makes it harder for the heart to pump blood effectively. If left untreated, HCM leads to congestive heart failure and death. Hypertension will cause damage to major organs, including kidneys, eyes, and heart.
Symptoms of hyperthyroidism include excessive drinking and urination, weight loss, irritability, increased appetite, increased activity, vocalizing, dull, dry, matted haircoat, vomiting, diarrhea, and sudden blindness, or decreased vision. The diagnosis is suspected when your veterinarian can palpate the enlargement of the thyroid gland in the neck. They may also hear a heart murmur, detect vision changes, and hypertension. Blood work will confirm the diagnosis. An ultrasound of the heart (echocardiogram) will reveal enlargement of the heart, and you may hear this referred to as a “valentine-shaped” heart, which is not normal. Repeated blood work may be necessary to confirm the diagnosis, and rule out concurrent diseases such as kidney disease and diabetes.
There are several ways to treat hyperthyroidism: medication, surgery, radioactive iodine and diet.
Most commonly, medication is used to decrease the production of excess thyroid hormones. These medications need to be given for the life of your cat and the dose my need to be periodically adjusted. This is accomplished by blood work and noting return of previous symptoms such as weight loss and increased appetite.
Surgery to remove the thyroid gland is an effective cure however not all cats are good surgical candidates due to age or physical conditions.
Radioactive iodine is considered the best treatment resulting in a 95% cure rate. It involves the injection of radioactive iodine which causes the destruction of the abnormal thyroid tissue. The advantages of this treatment are that no further treatment is necessary and fewer secondary health complications if treatment is given early. The disadvantages are initial cost and that the cat must stay at a licensed facility for 1-2 weeks.
A prescription diet for hyperthyroid cats is the least successful treatment but may help cats with no other options or in addition to other modes of treatment.
If your cat begins to lose quality of life, please consider and an end of life discussion with Dr. MaryJane. She is here to help with those decisions and can provide compassionate in home euthanasia for your beloved kitty.
