Mystery disease stalks older cats.

Mystery disease stalks older cats

Around 1980, veterinarians began noticing that some cats were displaying symptoms similar to those of humans with a hyperactive thyroid gland: weight loss despite a healthy apetite; high-strung activity; rapid heart rate; overactive gut; high-volume stools. Initially a rare disease, feline hyperthyroidism has mushroomed to epidemic proportions in some regions of the United States, according to Leslie Bullock, a veterinarian studying the disease at Tufts University in Boston. Baffled vets are trying to determine what's causing this disease and why it strikes only older cats.

Bullock says the disease may affect one in 100 cats 8 years old and older in the most highly affected regions, like Boston and New York. Veterinarian Mark Peterson, a feline hyperthyroidism expert at the Animal Medical Center in new York City, says the disease really is becoming more common: "It's not just that we're diagnosing it more because we know what to look for now."

Untreated, an affected animal would likely die from heart failure or malnutrition. Detecting the disease, however, is not very difficult, and there is effective treatment: controlling thyroid activity with a daily pill, removing the affected thyroids, or radiation therapy.

So far, Bullock says, vets have been unable to correlate the disease with diet, disease history, an urban environment or whether the animal spends time outdoors. However, she says, data from cats treated surgically for the disease suggest that some circulating factor -- such as an antibody -- might be responsible.

That possibility is especially provocative, bullock says, because the human disease that feline hyperthyroidism most resembles -- the relatively rare toxic multinodular goiter -- is initiated by the development of antibodies that mimic the activity of the hormone that controls thyroid activity. But because no such antibody has yet been found in cats with hyperthyroidism, Peterson says that "these cats have a different disease."

Though incidence data are still largely anecdotal, the disease seems to be most common in large East Coast cities and in California, and least common in the Mid-west, according to Peterson.

At the New York State College of Veterinary Medicine, in Ithaca, N.Y., Janet Scarlett Kranz is just completing an epidemiologic survey in the hope of identifying predisposing factors, such as pesticide exposures, sharing a household with an already affected cat or differences in iodine consumption. What concerns all the vets is a suspicion that some environmental factor -- such as exposure to a pollutant -- might be reponsible. If so, they say, these older cats may be a harbinger of what's in store for other species -- including humans.