Migraine aura sometimes accompanies or precedes migraine pain, but the phenomenon is difficult to treat and poorly understood. However, some evidence points to potential neurological mechanisms, and migraine aura is associated with cardiovascular disease risk.
Dr. Andrea Harriott
Andrea Harriott, MD, PhD, said at the Stowe Headache Symposium sponsored by the Headache Cooperative of New England, which was conducted virtually. Dr. Harriott is assistant professor of neurology at Massachusetts General Hospital in Boston.
Somewhere between 20% and 40% of patients with migraine experience aura. It is most often visual, though it can also include sensory, aphasic, and motor symptoms. Visual aura usually begins as a flickering zigzag pattern in the central visual field that moves slowly toward the periphery and often leaves a scotoma. Typical duration is 15-30 minutes. Aura symptoms are more common in females.
Research in the 1940s conducted by the Brazilian researcher Aristides de Azevedo Pacheco Leão, PhD, then at Harvard Medical School, Boston, showed evidence of CSD in rabbits after electrical or mechanical stimulation. He observed a wave of vasodilation and increased blood flow over the cortex that spread over nearly the entire dorsolateral cortex within 3-6 minutes.
In the 1940s and 1950s, researchers sketched on paper the visual disturbance over 10 minutes, tracking the expanding spectrum across the visual field, from the center toward the periphery. The resulting scotoma advanced across the visual cortex at a rate very similar to that of the cortical spreading observed by Dr. Leão, “potentially linking this electrical event that was described with the aura event of migraine,” said Dr. Harriott. Those researchers hypothesized that the aura was produced by a strong excitation phase, followed by a wave of total inhibition.
More recent functional magnetic resonance imaging studies have also shown that CSD-like disturbances occur when patients experience migraine aura. In one study, researchers observed an initial increase and then a decrease in the blood oxygenation level dependent (BOLD) signal, which spread slowly across the visual cortex and correlated with the aura event. “This study was really important in confirming that a CSD-like phenomenon was likely the underlying perturbation that produced the visual aura of migraine,” said Dr. Harriott.
Despite the evidence that CSD causes migraine aura, its connection to migraine pain hasn’t been firmly established. But Dr. Harriott presented some evidence linking the two. Migraine aura is usually followed by pain, and aura precedes migraine attacks 78%-93% of the time. Cephalic allodynia occurs in migraine about 70% to 80% of the time, and migraine with aura is more often associated with severe cutaneous allodynia than is migraine without aura. Finally, migraine patients with comorbidities have more severe disability, and more frequent cutaneous allodynia and aura than does the general migraine population (40% vs. 29%).
All of that suggests that activation of trigeminal nociceptors is involved with migraine aura, according to Dr. Harriott. Preclinical studies have also suggested links between CSD and activation of trigeminal nociceptors, with both immunohistochemical and electrophysiological lines of evidence. “These data suggest that spreading depression actually activates trigeminal nociceptors that we know are involved in signal pain in the head and neck, and that we know are involved in cephalic allodynia as well,” Dr. Harriott said.
The evidence impressed Allan Purdy, MD, professor of medicine at Dalhousie University, Halifax, N.S., who was the discussant for the presentation. “It’s an excellent case that CSD is a remarkably good correlate for aura,” he said during the session.
Along with potential impacts on migraine pain, aura is also associated with cardiovascular risk. “This is really important to know about in our clinical population,” said Dr. Harriott.
Meta-analyses of case control and cohort studies have shown associations between migraine aura and vascular disorders such as ischemic stroke. One meta-analysis showed about a twofold increased risk associated with migraine compared with the nonmigraine population. This difference was driven by migraine with aura (relative risk [RR], 2.25; 95% confidence interval [CI], 1.53-3.33) rather than migraine without aura (RR, 1.24; 95% CI, 0.86-1.79). Migraine generally is associated with greater risk of myocardial infarction (adjusted hazard ratio, 1.33; 95% CI, 1.08-1.64), and that association may be stronger in the aura phenotype.
There doesn’t appear to be evidence that traditional risk factors for heart disease – such as hypertension, diabetes, or high cholesterol – play a role in the association between aura and heart disease. One possibility is that variables like platelet activation, hypercoagulable state, or genetic susceptibility could be responsible.
The risks associated with migraine aura should be noted, but with a caveat, according to Dr. Purdy. “Even though the relative risk is high, the absolute risk is still relatively low, and patients with migraine with aura, who smoke or are female and over 45, those are the cases where the worry comes in.”
Dr. Harriott and Dr. Purdy have nothing to disclose.