Women with migraines accompanied by a visual disturbance called an aura are more likely to incur subtle, microscopic brain damage than are women without migraines, researchers report in the June 24 Journal of the American Medical Association.

A second study finds that women who have frequent migraines with an aura are four times as likely to have a stroke in subsequent years as are women without migraines. That finding, reported online June 24 in Neurology, bolsters previous studies linking migraines with stroke.

Auras often appear as arcs of sparkling light or blurry spots.

Although the new reports may appear frightening, they don’t reveal whether migraines are causally connected to strokes or vascular damage by any known biological mechanism, says Tobias Kurth, a neurologist and epidemiologist at INSERM, the French national health and medical research agency in Paris, and a coauthor of the report in Neurology.

In the study in JAMA, Lenore Launer, a neuroepidemiologist at the National Institute on Aging in Bethesda, Md., and her colleagues tapped into a registry of more than 4,000 people in Iceland whose health has been monitored since 1967. In these people, magnetic resonance imaging done 25 years after the start of the registry recorded any evidence of tiny brain lesions.

The researchers used these MRIs to establish that 23 percent of women who had a history of migraines with aura also had microscopic brain damage, compared with 15 percent of women without a history of migraines. After adjusting for differences in the groups, the researchers determined that the migraine-with-aura group was 1.5 times as likely to have these lesions as were the other women.

The data don’t establish that migraines with aura directly cause the damage, Launer says. It’s not even clear what the risks of having the lesions might be. “These look like very tiny strokes, but we don’t know what the functional consequences of these lesions are,” she says.

But if the migraines and these lesions are shown to be causally linked, the findings would cast doubt on the old notion of migraines as transient headaches that disappear with no lasting effect, Launer says.

For the time being, “it is premature to conclude that migraine has hazardous effects on the brain,” Kurth and physician Christophe Tzourio, also at INSERM, write in an editorial in the same JAMA issue.

In the other study, Kurth and his colleagues analyzed data from more than 27,000 U.S. women, a group that included more than 2,500 with migraines, 1,095 of whom also had auras.

Women who had a history of migraines with auras once a week or more faced a fourfold increase in the likelihood of having a stroke during the 12 years of the study compared with women who didn’t have migraines.

Kurth cautions that the incidence of stroke in women with migraines with aura in this study, while higher than in other women, was still very low—roughly a 3 percent risk.

Because the absolute risk of stroke in this study was small, Kurth says he doesn’t want to scare people who have migraines into thinking they are in imminent danger.

But evidence continues to link migraines to stroke and other ailments. Recently, a study found that women who have migraines during pregnancy face a heightened risk of strokes during that time (SN Online: 3/10/09). Other researchers linked migraines to heart attacks and strokes in women (SN: 7/22/06, p. 54). And an earlier study tied migraines to heart attack risk in men (SN: 5/26/07, p. 333).

Kurth says that population studies such as these attract researchers who may one day explain the phenomenon. “Epidemiologists, clinicians and hard-core basic scientists are now jointly trying to develop models to understand this data,” he says.

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