The Emerging Relationship Between Migraines With Aura And Stroke
Example of a blind spot in the right peripheral field of vision during a visual aura. Image generated with AI tool imagine.art.
Imagine you are sitting on a park bench, with a fountain in front of you and statues on either side visible in your peripheral vision. As you’re looking at the fountain you suddenly find that there are wave like patterns moving across your visual field, and these patterns migrate to your right visual field over the next few minutes. As these visual illusions end, you notice you cannot see the statue out of your periphery anymore, as there is a blind spot in your right peripheral visual field that lasts a few more minutes. These are called visual auras, and they tend to be accompanied by migraines.
Migraines are a highly prevalent and potentially debilitating medical condition that can negatively impact an individual’s quality of life. It has been estimated that around 1 billion people have experienced migraines, with the prevalence being doubled in females compared to males. About 20-30% of migraines are accompanied by auras, which can be visual illusions such as wavelike patterns, often followed by a blind spot in the visual field. These visual auras and accompanying migraines can prevent one from participating in everyday activities like driving, hobbies and even their job. Although the causes and mechanism of migraines are not entirely understood, studies have made headway in understanding what happens in the brain during visual auras, and the likely causes that trigger them.
Our brains are organized in a way that different brain areas are responsible for different functions, and when a certain brain area is being used, its activation can be visualized through tools like functional magnetic resonance imaging (fMRI). Similarly, a reduction of activity in brain areas can also be seen through these brain scans. Through fMRI scans of brains of people experiencing visual aura, it was found that there was ‘spreading depression’ in the cortical areas responsible for processing visual information, called the visual cortex. This means that there was an overall reduction in the brain’s activity that spread over the neighboring brain areas. The visual cortex is organized in such a way that it can be mapped to the real-world perception. The study found that during visual auras this suppression of brain activity can spread from the areas that process the center of vision to areas responsible for peripheral vision. This is similar to how visual auras manifest, where the wavelike patterns and even blind spots can move from the center visual field to peripheral, as was seen in the park example earlier in the article.
This brings into question the cause of these visual auras and migraines. There is increasing evidence that visual auras may be caused by small particles in the arteries, called microembolisms. It has been shown that microembolisms can trigger cortical spreading depression, which is likely through temporarily preventing blood flow to brain areas. Emboli can be of several origins, including blood clots, plaques, tumors, and even air. In a past study, microemboli that traveled into mice brains resulted in reduction of brain activation similar to cortical spreading depression. The study showed that these events did not leave permanent damage to the brain. Our bodies are capable of breaking down small particles like blood clots, which is likely why these microembolisms did not result in brain tissue damage.
However, there is a connection between migraines with aura and stroke, as people who experience migraines are at a higher risk of having a stroke. A stroke involves damage to brain tissue as a result of a prolonged loss of blood flow, which can be caused by damage to the blood vessels or embolisms such as blood clots. It is increasingly thought that microembolisms underlie migraines, especially those with visual auras, which can also cause stroke if they are not broken down. The timely breakdown of emboli before permanent brain damage is thought to depend on the size of the emboli, and could potentially be the difference between a visual aura and a stroke.
A recent review paper from a team of experts at Western University highlights evidence for the theory that microembolisms are the underlying cause of migraines with aura, and outlines the known risk factors for strokes. They summarize several factors that are known to increase the risk of stroke, including genetic predispositions, certain medications, hormonal contraceptives, atrial fibrillation, and arterial dissections. Many of these factors increase the likelihood of blood clot formation. Blood clots originating from the heart pose a high risk for stroke, and it is suggested that microembolisms from the heart may then also be the cause for migraines with aura. Furthermore, injuries to the arteries have also been associated with visual auras, and can also be origins for blood clots. These recent papers suggest that microembolisms that can originate from various causes are the common link between stroke and migraines with aura. The relationship between migraine with aura and stroke is further strengthened by a case study described in the review paper by Sacco and colleagues, in which a patient experienced an episode of severe migraine with aura as well as speech issues, and an MRI scan revealed a small area of brain tissue damage, indicating there was a prolonged loss of blood flow to the area. This recent review sheds light on the previously unknown cause of migraines with aura, and understanding the origin could open up potential avenues for treatment.
In conclusion, migraine with aura has been associated with increased risk of stroke, and it is increasingly thought that they may have shared origins. Namely, microembolisms originating from several potential underlying causes. However, further studies on this subject are required as there needs to be direct causal evidence linking microembolisms and migraines with aura, since the study establishing this causal relationship was done in mice. Understanding the underlying cause of migraines with aura in individuals may help us better address these causes to not only improve their quality of life, but also potentially prevent strokes, which is one of the leading causes of disabilities in the world.
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