WEDNESDAY, June 16, 2004 (HealthDayNews) -- To their surprise, Viennese researchers have found that men who have had one life-threatening deep vein clot are much more likely than women to have a recurrence.
"Up to now, we do not have a ready explanation for this finding," said Dr. Paul A. Kyrle, an associate professor of medicine at the Medical University of Vienna and lead author of a report published in the June 17 issue of the New England Journal of Medicine.
"It is counterintuitive to everything we thought," said Dr. Lewis J. Rubin, a professor of medicine at the University of California, San Diego and co-author of an accompanying editorial.
Deep vein clots -- the formal medical name is venous thromboembolism -- are often called "economy class syndrome," because leg clots can result from the cramped conditions of low-priced airline seats during a long flight. But anyone can suffer a deep vein clot, and a person who has had one clot is at high risk of having another.
Preventing a recurrence is one of the trickier problems in medicine, because too-high doses of the anticoagulant drugs used to prevent clots can cause damaging brain hemorrhages.
The study followed 826 patients for three years after a first deep vein clot, when anticoagulant treatment had been stopped. It found more than a threefold higher incidence of second clots in men -- 74 of 373 males compared to 28 of 453 women.
The Viennese researchers are more or less guessing about the reason for the difference between the sexes, Kyrle said. "We speculate that women have a protective factor that lowers the risk for thrombosis," he said. "We are currently investigating the role of female hormones."
"I don't have a good answer for it," Rubin said. "Intuitively, we thought that being female was more likely to be a risk factor. Either women are more protected or men are more vulnerable, and I'm not sure which is correct."
Both Rubin and Kyrle said more studies are needed to confirm the difference between the sexes. But both said the findings will affect their medical practice to some degree.
"One must consider that women, especially young women, have a very low risk of recurrence," Kyrle said.
"I'm not yet ready to extrapolate from this paper to treat men with anticoagulants for a longer period," Rubin said. "I am ready to enhance my suspicion for recurrence in males, so that any sign or symptom, however subtle, needs to be addressed promptly."
But whether men who have one vein clot should take anticoagulants for longer periods than women is not yet known, Rubin said.
"This is a very intriguing finding that will prompt additional studies to answer the key clinical question," he said. "Should we be treating men for a more protracted period than women?"
An explanation of economy class syndrome and how it can be avoided is available at the American Heart Association.