Hyperthyroidism in Cats

Following the Treatment of a Hyperthyroid Cat



November 21, 2002

Bubba was diagnosed with hyperthyroidism following a rapid onset of clinical signs. He is a well-nourished 15 year old cat with an excellent health history with minor exceptions: a crisis with urinary crystals several years ago, and an undetermined illness that struck when he was 12. He is also the alpha cat of our 3-cat household, which also includes Jaspurr and Joey.

The Diagnosis

Because of his age, we watch Bubba closely for signs of illness. Despite this, his hyperthyroidism eluded us for a while as the signs were vague. We noted he was unusually grumpy, which we attributed to his dislike of little Joey (although he seems to love Jaspurr). We also noticed he preferred to spend more time alone and asked to go outdoors for increasing periods of time.

We first became concerned when Bubba began vomiting several times a day. While not unusual for him to vomit after eating, these episodes were more frequent. This quickly progressed to Bubba becoming inappetant. At that point, we immediately brought him to his veterinarian. I suspected IBD (Inflammatory Bowel Disease), because we had discussed this possibility in the past. I was surprised when his veterinarian said he could feel Bubba's thyroid glands, and that hyperthyroidism was a possibility. Bloodwork (thyroid panel) confirmed this diagnosis. Bubba's thyroid level (T4) was 6.5 (normal ranging from 0.7 - 5.2.)

The Treatment

Bubba was given an anti-vomiting injection during his first veterinary visit and was prescribed medication for use to administer at home for vomiting. Once the diagnosis of hyperthyroidism was made, he was started on another medication called Tapazole (methimazole). This is a tablet given by mouth, twice-daily. The plan was to recheck labwork in two weeks. He was also prescribed an appetite stimulant.

By the second day of treatment, Bubba was already starting to resemble his "old self." He resumed eating. When we served him his first meal after his initial dose of medication, he stared at me, as if to say, "Why do you hate me, Mom?" Shortly after, he visited the J-Boys' plate and finished off what they had left. I guess "stolen food tastes better" is the rule!

The Follow-Up Visit

Hyperthyroidism can mask occult (hidden) kidney disease. Although Bubba's kidney and liver values were normal before starting treatment, we planned to recheck lab work two weeks after starting therapy to ensure they remained within range. One alternative treatment option to lifelong oral medications is radioactive iodine. The benefit of this treatment is it eliminates the need to keep giving Bubba pills every day. We were considering this option for Bubba and knew to be eligible for this treatment, he must have healthy kidneys and a healthy heart, so we planned on more testing with this option.

Bubba's diagnosis emphasizes the importance of annual examinations and bloodwork for senior cats, a policy I've endorsed but didn't adhere to the year he was diagnosed. Had Bubba received a full examination earlier in the year when he received his three-year rabies vaccination, we may have caught this disease earlier and avoided the stress of a rushed visit to the vet's office.

The Followup Tests

Bubba's thyroid level was rechecked after two weeks of Tapozole therapy. We saw positive results at home, as his appetite had returned to normal and he appeared to even have gained a little weight and wanted to ensure his T4 level was reducing appropriately.

We anxiously awaited the results and were thrilled to hear that Bubba's T4 had reduced to 3.3, which is mid-range of normal. He also regained almost half a pound, and his kidney and liver values were still normal. This meant he was a good candidate for radioactive iodine therapy, our treatment of choice.

What Comes Next?

We are currently exploring options for radioactive iodine treatment near where we live. In the meantime, Bubba continues to thrive, and he's accepted his medication as part of his new routine and is eating well with minimal vomiting. We can treat him with Tapazole as long as it works for him and he tolerates it. Except for the unlikely scenario of the tumor being cancerous, there's no rush for radioactive iodine treatment. In the meantime, we will continue to monitor Bubba's appetite and energy level and note any changes in frequency of vomiting or weight loss. His T4 level will be monitored twice yearly, along with a full blood panel and blood count.

Disclaimer : The author is not a veterinarian, and this history is not necessarily typical for a hyperthyroid cat. Only a veterinarian is qualified to diagnose and treat your cat for hyperthyroidism.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.
Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Hyperthyroidism in Cats. VCA Hospitals.