Cat Hyperthyroidism: My Senior Cat Is Shrinking

Hyperthyroidism is a common disorder in senior cats. The good news is that it’s fully curable or controllable.

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A cat who eats well but is losing weight could be suffering from hyperthyroidism. hagit berkovich/iStock/Thinkstock

Weight loss in many cats, especially longhaired cats, can be elusive. It progresses for a while without notice. Then, one day, it appears that you have less cat than you used to have. You feel bones that you have never felt. If your senior cat has been overweight, you may actually pat yourself on the back for being such a responsible cat parent.

At some point you begin to realize that this amount of weight loss is really not something to celebrate. But your denial continues as you recall how great your cat’s appetite has become. Surely a cat who eats that well cannot really have an illness. As that thought passes, your imagination starts thinking about the causes of weight loss. Diabetes and cancer are at the top of the list. Now your joy turns into panic and dread. You know that a diabetic cat requires shots every day. Not good. Even worse are the prospects of what you face if your cat has cancer.

Your Skinny Cat Needs A Veterinary Visit

After days of denial, you realize that a trip to the vet is inevitable. You pick up the phone and make the call. You and Sylvester can be seen at 3 p.m. on Wednesday. However, as the time comes to gather up Sylvester and make the journey, it seems that he had been reading your mind. He is nowhere to be found. You look in his known hiding places, and it is as if he has disappeared. Finally, you find him behind the refrigerator. After several minutes of pleading, threatening, bribing, promising and coaxing, he is tempted by tuna. You grab him and put him in the carrier. Off you go to the sounds of a wailing Sylvester.

The loading episode has delayed you, but Dr. Green is understanding. He knows the challenge you faced because he hears this story every few days. Margaret, the technician, begins the process with your account of Sylvester’s history. You express concern about his weight but dismay because he is eating so well. Margaret is not shocked because she has heard this history many times.

Dr. Green enters the room and greets you and Sylvester. Because he has seen Sylvester for many years, he immediately realizes that there is a weight problem. It’s not the weight loss from diet and exercise; it is the bone-protruding kind that signals the need for medical attention. He looks at Sylvester’s gums and listens to his heart and lungs. He feels his abdomen and then asks about thirst and urination. His skilled fingers slide up and down Sylvester’s neck; a look of relief comes on Dr. Green’s face and brings a warm glow to your face. Sylvester is oblivious, but enjoying the attention, even if it is a bit weird.

Dr. Green announces that Sylvester’s thyroid gland is too large. He suspects hyperthyroidism but needs confirmation with some blood tests. He also states that the blood panel will be looking for other causes of weight loss, including kidney disease and diabetes. Cats more than 10 years of age commonly have all of these.

A Diagnosis Of Hyperthyroidism

The blood panel confirms hyperthyroidism. Sylvester’s total T4 level is far above normal, which correlates with thyroid enlargement, weight loss, increased appetite and the rapid heart rate that Dr. Green heard with his stethoscope. Now, you hold your breath to find out if hyperthyroidism is treatable and what the outcome will be. Dr. Green tells you that there is a tumor in the thyroid that involves both lobes. He adds that a tumor also could be in the extra (ectopic) tissue that is in the neck and the chest. Your anxiety rises as he tells you there is a 98 percent chance that the tumor is benign. He tells you that there are two ways to control the disease and two ways to cure it; either form of treatment should return Sylvester to his old robust self. Your anxiety begins to subside a little. You like the idea of having the old Sylvester back and you definitely like the word “cure,” but you also want to hear about “control.”

This cat's long hair coat made it difficult to detect his weight loss until it became severe. Courtesy of Dr. Gary D. Norsworthy

This cat’s long hair coat made it difficult to detect his weight loss until it became severe. Courtesy of Dr. Gary D. Norsworthy

Treatment For Hyperthyroidism In Cats

Control can occur by eating a special, iodine-restricted diet. It has to be exclusive, and it has to be long-term. Control can also be achieved by giving Sylvester tablets every day. Because Sylvester is only 12 years old, the thought of a special (and expensive) diet or tablets for the next eight years is not too appealing. You want to hear about what it takes to cure this disease.

Cure can be achieved either with surgery or with radioactive iodine. Your enthusiasm wanes. Surgery sounds rather invasive. However, Dr. Green is quick to state that cats with disease in both thyroid lobes are not really the best candidates for surgery. He begins to discuss radioactive iodine therapy. He says radioactive iodine is not as scary as it sounds. In fact, he is quick to tell you that he had a tumor on his thyroid that was treated this way. The radioactive particle is given by a single injection under the skin or taken as a pill. The iodine in it carries the radioactivity to the thyroid, sparing other tissues. The tumor is killed, and the normal thyroid cells are spared. Sylvester ends up with no thyroid tumor and a normal thyroid gland. Life will be good again.

The only problem is Dr. Green does not do this treatment, so you will have to find someone who does. Fortunately, you live in a large city with a veterinary referral center. It can be done there even though you will have to travel about 40 minutes to get there — that’s 40 more minutes of Sylvester howling. And once Sylvester is treated, he must stay there for about four to seven days because the state requires that Sylvester lose nearly all of his radioactivity before going home. Sylvester has never been away from home, and you tell Dr. Green you’re concerned about how your senior cat will manage. Dr. Green assures you that you will probably take this harder than Sylvester, as cats are quite adaptive to new surroundings. With Dr. Green’s blessings you make the decision to have this treatment performed by Dr. Brody, the specialist.

The treatment is done on Monday, and Sylvester is discharged on Friday. He looks just as thin as he did before treatment, but Dr. Brody assures you that in about two to three months Sylvester will regain his weight. You do not have to give him any medication, but you do have to keep him indoors for about two weeks.

The Outlook After Hyperthyroidism Treatment

Dr. Green’s receptionist calls you in one month to remind you that Sylvester needs to have his thyroid level checked to be sure the treatment was successful. You do so and find out that the level has gone from too high to a little too low. However, Dr. Green assures you that Sylvester’s thyroid function will improve over the next one to two months as those normal thyroid cells that went to sleep because the tumor was making too much thyroid hormone will wake up and go back to work. He tells you that the temporary low thyroid function will actually help Sylvester regain some of his weight more quickly. As the thyroid cells function again, Sylvester will regain his lost weight then level off.

More than 90 percent of cats with hyperthyroidism have a very good outcome to treatment. Before you know it, the old Sylvester will be back.

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Cats · Health and Care