NEW YORK (Reuters Health) – The findings of a new study suggest that, contrary to what some researchers have hypothesized, migraine is not associated with atherosclerosis, also referred to as harding of the arteries, but it may be a risk factor for blood clots in the veins.

A serious complication, called venous thromboembolism, may occur if the blood clot dislodges into the circulation and blocks a major organ, such as the heart or the brain. This may induce a heart attack or stroke.

In several prior studies, migraine has been linked to an increased risk of cardiovascular disease, particularly stroke. The underlying mechanisms, however have been unclear, according to the report in the current issue of the medical journal Neurology.

“The thinking has been that because people with migraine are more likely to have strokes and other cardiovascular problems, that they would also have more severe and early atherosclerosis,” study co-author Dr. Stefan Kiechl said in a statement.

“This study is the first to use high-resolution ultrasound to examine this theory, and it provides solid evidence to refute it,” he said.

The findings are based on an analysis of data for 574 patients, 55 to 94 years of age, who participated in the Bruneck Study, a population-based investigation conducted in northern Italy. The subjects, who were followed from 1990 to 2005, were interviewed regarding headaches and venous thromboembolism. They also underwent ultrasound testing to assess atherosclerosis in the femoral and carotid arteries, two important arteries that supply oxygen-rich blood to body.

Based on standard diagnosis criteria, 111 subjects had migraines, including 36 with aura. Patients with or without aura were no more likely than non-migraineurs to have atherosclerosis, and there was no difference in severity or 5-year progression of atherosclerosis between the groups. In fact, there was a tendency for atherosclerosis to be less severe among the migraine patients.

As noted, however, migraine patients did seem to be at increased risk for venous thromboembolism. Overall, 18.9 percent of migraineurs developed venous thromboembolism compared with 7.6 percent of non-migraineurs, a statistically significant difference.

Migraineurs’ blood may be prone to coagulate more easily than normal, the authors continue, which can be “considered an alternative explanation for the increased cardiovascular disease risk among patients with migraine.”

A new finding from the Bruneck Study is the discovery of “a significant association between migraine and lifetime risk of venous thromboembolism.”

SOURCE: Neurology, September 16, 2008.

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