Despite its high prevalence and typically benign nature, migraine-associated aura remains for many a mystifying and often frightening neurologic symptom. Witness the following description provided by Cynthia A, a veteran migraineur:
It was just my usual run. Six miles along city streets and sidewalks during the peak heat of a Gulf Coast summer day. I was 23 years old at the time and a bit of a fitness fanatic. With my favorite tunes blasting through my headphones, my feet pounded rhythmically on the sidewalk. The day’s stress was easing off, and despite the sweat I was feeling refreshed and relaxed. All was well as I rounded the corner at Dauphin and Government, ready for the final mile. Then something very strange happened. Something unprecedented and a little terrifying.
This was the home stretch. Along my route was a large high school campus surrounded by a tall wrought iron fence with vertical bars spaced about a foot apart. The sun was beginning to set, and, strobe-like, it flickered brightly between the bars as I ran by. Red-faced and drenched in sweat, I began to sprint for my imaginary finish line that lay just beyond the fence.
Suddenly I stopped. There was something odd about my vision. A blob of distortion had appeared to the left of center, like a bright white light refracted through a prism. I rubbed my eyes, but nothing changed. When I closed my eyes, I saw the blob in the very same place. Over the next 15 minutes the area of visual distortion enlarged to the point that I couldn’t see well enough to find my way home. Then the blob transformed into a lines of angles that progressively widened and gradually faded away. My vision seemed fine, but I began to develop a terrible headache. The headache was not so unusual; just like my father, I’d struggled from time to time with “go to a dark, quiet room” headaches…but never were they accompanied by any such visual oddity. The next morning I awoke with no headache and my vision entirely normal.
I called my primary care provider and was referred to a local neurologist. The earliest available appointment was in three weeks, and for those weeks I quietly obsessed about the strange visual episode. What had caused it? Was there a tumor growing inside my brain? Did I have an aneurysm? Were alien bacteria colonizing my eye? Whatever it was, I was convinced it must be serious. To make matters worse, the same symptoms occurred a few days later, at precisely the same time during my accustomed run and just beyond the wrought iron fence with the flickering sunlight.
My visit to the neurologist provided little comfort. He examined me in near-complete silence, and I decided he must be deciding how best to break the bad news. At the end of the appointment, however, he simply told me I needed some tests. He ordered a brain MRI scan (yikes!) and an EEG (gulp!), presumably to better define the horrible fate awaiting me.
But at my follow-up appointment a week later he pronounced my diagnosis: “migraine with visual aura”. No life-threatening tumor. No exploding aneurysm. No nasty bacteria. It’s genetic, he explained. A gift from your father. I nodded agreeably, all the while thinking “I have absolutely no idea what he means.”
Flash forward 26 years to the present. I now know a lot more about migraine and the aura which may accompany migraine. I have continued to experience exactly the same aura - sometimes provoked by bright flickering lights and sometimes not, usually (but not always) followed by a headache. The aura tends to occur if I am menstrual, dehydrated or stressed, but at other times it will visit me for no apparent reason. It has become not a friend, really, but definitely a familiar companion. And instead of panicking when the small white prism appears in my left visual field, I go take some aspirin and relax.
Cynthia’s story is familiar to health care providers who frequently treat migraine. Upwards of 36 million Americans – more than 1 in 10 – are actively afflicted by migraine, and as many as 9 million will at least occasionally experience aura. Aura is a common reason for migraineurs to seek medical attention, and many of those who do will undergo MRI scans and other testing that typically adds little beyond financial expense and patient inconvenience. So if aura is so common and benign, why all the fuss?
As is true of migraine generally, high prevalence does not equate with a clear understanding. Like Cynthia, many of those with long-established migraine are shocked by their first experience with aura. Conversely, many people (including doctors) believe that what we term "migraine" must involve aura which invariably is followed by a severe headache that is throbbing in character and accompanied by nausea, vomiting, and sensitivity to light and sound. The reality: although many of the 36 million Americans afflicted by migraine do at times suffer migraine attacks that match up perfectly with what is described, in only a very few does their migraine always involve this stereotyped array of symptoms.
A migraine attack may consist of only aura and no headache whatsoever (see section on Ocular Migraine in this issue), or it may be expressed as incapacitating head pain… or as any degree of pain on the spectrum between these 2 extremes. Be it mild or severe, most headaches suffered by a migraineur are "migraines" that result from the same underlying biologic process.
While only 20-25% of migraineurs ever experience aura, the majority of migraineurs at times experience a prodrome prior to their headache attacks. The symptoms of a migraine prodrome typically are vague or nonspecific (commonly occurring examples are euphoria or depression of mood, hyperactivity, food cravings (eg, sweets or salt) and repetitive yawning). Vague or not, the experienced migraineur often learns to identify those symptoms as a reliable indicator that headache is soon to follow.
Again, no more than a quarter of migraine patients will ever experience aura, and in only a very few is aura a component of each and every attack. The symptoms of aura are much more specific and strictly "neurologic" than those of the migraine prodrome. As Cynthia experienced, aura symptoms typically possess both "negative" features (for example, vision loss) and features which are "positive" (as examples, geometric patterns, flashing or shimmering lights, "heat waves rising") perceived with one or both eyes.
Aura symptoms tend to be dynamic, building in their intensity before receding and vanishing. The symptoms usually develop gradually over 5-20 minutes and last for less than 60 minutes. In a substantial number of migraineurs, however, aura symptoms may come and go for a much more extended period, and in a small minority of migraine suffers aura may persist for weeks or months.
Headache usually follows the aura, but in some cases the headache may begin before the aura or before the aura has stopped, and, as mentioned previously, aura symptoms can occur without any temporally associated head pain at all. While prodromal symptoms tend to occur many hours before the headache phase of a migraine episode, headache typically follows right on the heels of an aura.
The most common migraine aura involves visual symptoms, but many migraineurs experience sensory aura. Sensory aura often begins with numbness (loss of sensation: a negative feature) and tingling (a hallucination of sensation: a positive feature) affecting the lips and tongue and one side of the face, spreading to involve the cheek and then gradually extending to involve the hand on that same side. Many patients with sensory aura also describe "heaviness" of the affected limb, and not surprisingly sensory aura frequently is misdiagnosed as a warning symptom of stroke or, less often, as a partial seizure. Patients may experience both visual and sensory aura within the same attack, with the symptoms occurring together or one after the other.
Aura symptoms are believed to arise as a result of electrochemical changes occurring in that portion of the brain which is relevant to the symptoms. For example, visual aura results from electrochemical event arising within the occipital lobes, the brain area which is primarily responsible for processing vision. If that genetically primed visual area is acutely exposed to a sufficiently compelling stimulus (eg, the “flickering sunlight” experienced by Cynthia), the neurons in that area react in a manner that produces aura. Whether that same electrochemical event is the origin of migraine head pain remains a source of controversy within the scientific community.
Many migraineurs report that with aging, aura aura symptoms become more prominent while the headache portion of their migraine attacks lessens or vanishes entirely. Again, these episodes of aura without headache occurring in the older population frequently are mistaken to be indicators of impending stroke.
Although migraine with aura is much, much more common than migraine causing stroke, the risk of stroke in migraineurs with aura is increased relative to that of the general population and relative to migraineurs who experience no aura. That risk may be further increased by the use of an estrogen-based oral contraceptive. While female migraineurs with aura consequently may wish to consider an alternative method of contraception, it should be emphasized that although their relative risk of stroke is increased by use of the OCP, the absolute risk associated with their OCP use remains extremely low.
If you are one of the minority of migraineurs who typically experience aura prior to headache onset, you may wish use this association to increase the effectiveness of the medication you administer for acute migraine treatment. Early treatment of migraine is critical to achieving a total elimination of symptoms and to lowering the chance of early headache recurrence. Think of your your aura as an ally… not an alien.