A common form of treatment for cats with overactive thyroids may not be working for some patients and may be causing secondary problems for others. Veterinarians at the Virginia-Maryland College of Veterinary Medicine at Virginia Tech and the VCA Veterinary Referral Associates in Gaithersburg, Maryland, are hoping their clinical research will address these gaps in treatment.
“Traditionally, most places across the country who treat hyperthyroid cats with radioiodine give a fixed dose,” said Greg Daniel, professor of radiology and head of the Department of Small Animal Clinical Sciences. “While a fixed dose is effective in eliminating the hyperthyroidism, there is a concern that we are overtreating the cats. The ‘one dose fits all’ approach results in an unacceptable number of treated cats — around 30 percent — becoming hypothyroid. By using the fixed dose, we tend to give more radioiodine than needed for a large proportion of cats, yet for a small number of cats that remain hyperthyroid, we are giving less than we should.”
David Panciera, the Anne Hunter Professor of Medicine, and Wendy Morré, small animal medicine resident, are leading a clinical trial at the Veterinary Teaching Hospital in Blacksburg that uses a technique called scintigraphy to measure the severity of thyroid disease. With support from the college’s Veterinary Memorial Fund, they are tailoring the dosage of radioiodine for cats enrolled in the study based on the intensity of radionuclide uptake and the size of the thyroid gland measured from the scintigraphic study.
Other researchers have improved treatment responses by altering the dosage of radioiodine based on serum thyroid hormone levels and clinical signs. Researchers at the college are hoping to provide objective criteria derived from scintigraphic studies to determine the dose of radioiodine that achieves the best treatment responses.
Last fall, researchers also teamed up with Tina Conway, a veterinary internal medicine specialist at VCA Veterinary Referral Associates who routinely treats hyperthyroid cats with radioiodine. Conway was already using scintigraphy to capture images of the thyroid gland in her clinical practice and adjusted her methodology to match the college’s approach so that her data can be used in the overall study. She recently treated her 200th cat.
“We are doing two studies in parallel,” explained Daniel, who is working on the imaging side of the study. “The veterinary college is looking at a series of radioiodine doses and will compare results with Dr. Conway, who used a different dose range. Eventually, we can combine the data so we can look at effectiveness across a broader range.”
The clinical research has already benefited cats enrolled in both studies. Myra Socher, of Rockville, Maryland, brought her 11-year-old tortoiseshell cat, Trixie, to Conway in Gaithersburg. Trixie underwent radioactive iodine therapy and is now recovering well.
“Hyperthyroidism is so common among cats,” Socher said. “This is my second cat with the condition, and I know of many others. We adore Dr. Conway, and we’re happy to do what we can to help researchers learn more about this disease.”
According to Daniel, most cats with hyperthyroidism are older than 8 years. Common clinical signs include weight loss, increased appetite, hyperactivity, gastrointestinal issues, an abnormal thirst, and high urine production. Although veterinarians can treat an overactive thyroid with diet, medicine, or surgery, the 2016 American Association of Feline Practitioners Guidelines for the Management of Feline Hyperthyroidisms stated, “Experts generally agree that radioiodine is the treatment of choice for most cats with feline hyperthyroidism.”
The research partnership is an example of the college’s Collaborative Research Network in action. The network, which was established in 2014, enables specialty practices in Virginia and Maryland to partner with the veterinary college to undertake cutting-edge research.
Efforts to help cats with hyperthyroidism are expanding with a new study partnering Stefanie DeMonaco, assistant professor of small animal medicine, with Conway. Also with support from the Veterinary Memorial Fund, the study is investigating the kidney biomarker SDMA, which may be able to help veterinarians predict kidney dysfunction in hyperthyroid cats. Like hyperthyroidism, chronic kidney disease typically affects older cats.
“There is a interaction between hyperthyroidism and chronic kidney disease, and often the hyperthyroidism will mask or hide the underlying kidney disease.” Daniel explained. “A veterinarian might be treating a hyperthyroid cat and not realize that the kidneys are not functioning well until the hyperthyroidism has been eliminated.”
The college’s Veterinary Clinical Research Office has more information about clinical trials involving companion animals on its website. To learn more or enroll an animal in ongoing clinical trial, contact Mindy Quigley, clinical research coordinator, at 540-231-1363.