Aura is basically secondary to what has been termed the cortical spreading depression, and what that means is that you have oligemia. You have blood flow decrease starting at the back in the brain and it moves forward. With this cortical spreading depression, the oligemia--the decreased blood flow--can be found in different hematological areas, in other words, the posterior circulation, the middle cerebral circulation, it just moves forward. So just like you see here with multiple dermatomes, you can see that with multiple areas of hematological activity. Everybody focuses on visual migrainous aura but there’s an extraordinary number of auras that are not visual, that are sensory, that are cognitive, things that one would not expect. For instance, a sensory aura I’ve seen probably a couple of dozen of times is called a cheiro oral migraine. Patients will develop numbness in their hands and their fingers, and it will go up their arm to about the elbow at which point it will jump to the ipsilateral side of the mouth. If you look at the homunculus in the motor strip of the brain, the thumb and fingers is right next to the corner of the mouth. So this aura really goes right where you expect it to. The other issue is that you can have more than one aura. You can have a visual aura that can last anywhere from 5 to 15 to 60 minutes and then have a sensory aura which may last 20 minutes to half an hour, and then have a third aura and then get your headache.
It’s important for the clinician to understand what the difference is, what’s going on. The first time a patient has a neurological aura, particularly if there’s no history of migraine, that calls for a full neurological evaluation--MRI, CT scan. The typical headache patient should not need MRIs, CT scans, or any of these tests. It’s a clinical diagnosis. But if you know that there is a history of migraine, or a family history, that makes it a lot easier to determine that unless something significant is discovered on exam, it’s not a problem.