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Strange Thyroid Malady Sweeping Cat World

July 24, 1992|MALCOLM GLADWELL | WASHINGTON POST

You may have thought there was enough bad news in the world. You are wrong. For reasons no one can explain, thousands of America's cats are coming down with a once rare glandular disorder.

The disease, a tumor of the thyroid, affects primarily middle-aged cats. Exceedingly rare in humans and unknown in other species, it results in the uncontrolled production of thyroid hormones, leading to severe weight loss, vomiting, diarrhea, skin disease, abnormal breathing and cardiac problems.

Veterinarians say that the outbreak defies explanation, although fingers have been pointed at everything from unknown viruses to the possibility that house cats are being slowly poisoned by commercial cat food. All that is clear is that the disease appears to strike without regard to breed or sex. And while it was unknown as recently as the 1970s, it is now nearing epidemic status among the nation's geriatric cat population.

"Basically I feel that any cat, if it lives long enough, will get this disease," said Jan Turrel, a San Francisco veterinarian.

Solving the mystery of the outbreak has become something of an obsession for the cat endocrinology community, with researchers across the country puzzling through seemingly contradictory pieces of evidence. In Japan, for example, where cats eat lots of fish, the disease is virtually unknown. Ditto for isolated South Africa, where cats apparently spend disproportionate amounts of time outdoors. But why is it well-known in New Zealand and not in neighboring Australia? Why is it big in Great Britain but not in Europe?

Consider the theories:

* Hyperthyroidism is a disease of old cats and cats are getting older. The skeptic's position. Because of better medical care, cats now live seven or eight years longer than they did in the 1970s. If this is a disease that cats naturally get when they are old, then it makes sense that we are seeing more of it now, especially since vets are now actively looking to make the diagnosis.

"I would be skeptical that this is an epidemic," said Paul Ladenson, director of the Johns Hopkins University Thyroid Tumor Center. "That's a common flaw with this type of pseudo epidemiologic investigation. Someone's cat gets hyperthyroidism. Then their neighbor's cat gets it, and suddenly everyone with a languid cat is taking it to the vet and getting diagnosed with hyperthyroidism."

But reviews of cat autopsies going back to the 1950s show a definite increase in thyroid problems over the past decade. And vets say that ever since they began looking for the disease in the early 1980s, the numbers have recently risen dramatically. One California vet says she used to see perhaps 10 cases of the disease in the early 1980s. Now she sees 500.

* Cats have caught a bizarre virus. Cats do get strange cancer viruses, including a leukemia virus belonging to the AIDS family. On the other hand, viruses have not been implicated in hyperthyroidism in humans. Plus, it is not clear how a virus could spread to so many cats all over the world, since house cats do not generally engage in the kinds of indiscriminate physical intimacies that characterize, say, humans.

* Cats are being poisoned by something in the environment. The evidence for this is scattered but intriguing. In theory, it is entirely possible that some kind of toxin could be the cause of the thyroid tumors. In humans, high levels of radiation are known to induce hyperthyroidism. So are certain chemicals, and in fact cat thyroids are known to be especially sensitive to the family of chlorinated hydrocarbons.

Perhaps, then, cats are acting as an early warning system for pollution that may someday affect humans, a whiskered canary in a coal mine.

The problem is that hyperthyroidism isn't seen much among farm cats, who are the most exposed to pesticides. It's a disease of house cats. The only obvious danger they face is radon, and there is no evidence that cats who spend inordinate amounts of time locked in basements, where radon levels are greatest, suffer disproportionately from the disease.

* Cats are eating bad cat food. Diet has been linked in the past with thyroid dysfunction, particularly because of the relatively common presence in plants and drugs of chemicals known as goitrogens, which can cause thyroid tumors. On top of that, cats metabolize many substances much slower than other species. As a result, the kind of chemical that irritates the thyroid lingers much longer in a cat's bloodstream than a human's.

Turrel points out one additional fact: Americans began moving toward feeding their cats exclusively commercial cat food in the late '60s and early '70s, moving cats away from the more variable diet of table scraps, mice and birds they had enjoyed previously. If there are some potent goitrogens in cat food, in other words, it would make sense that the first symptoms of slow developing hyperthyroidism would begin to show up about a decade later. The cat food companies say the idea is ridiculous.

* The mystery is unsolvable. Cats can't talk and they spend hours by themselves doing mysterious things. One researcher, who just completed a study of 500 sick cats, says he despairs of ever finding an answer. And, after all, who knows what kinds of risk behaviors they engage in? Who knows what cats do all day?

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