Transcription
So today we're going to talk about migraines. Migraines can affect up to 15% of the population, with women being affected more than men. Now, most people will tell you that a migraine is a headache, and that is true. It does result in terrible head pain. However, those who actually get migraines will probably tell you there's a little bit more to it than just simply a headache. So we're going to get into exactly what a migraine is. Learn that it's actually made up of multiple phases. And this will help us to understand the symptoms and even potential triggers that people can try to avoid in order to reduce their risk of getting migraines. And of course, we're obviously going to use some anatomical awesomeness to help us describe these migraines. So, let's do this.
So, let's start with the definition of a migraine. A migraine is a complex neurological disorder that can be divided into four different phases. And so we're going to discuss each one of these phases because it will help explain why people experience the many different symptoms of a migraine, which will also show us that this is more than just a basic headache.
The first phase of a migraine is called the pre-monitory phase. This can start up to 72 hours before the actual headache even starts. People can experience symptoms like fatigue, photophobia, which is light sensitivity, irritability, and sometimes even feel depressed. They can also notice that they might yawn more and have food cravings and even have stiffness in certain muscles, especially the muscles of the neck.
And so the next question might be, what is actually initiating or causing this premonitory phase? Well, it's believed that this is in part due to an alteration in homeostasis. And if you talk about homeostasis or keeping the body in balance and equilibrium, you have to talk about that wonderful structure called the hypothalamus. The hypothalamus is located in the central core of the brain, right underneath my probe here. And here are some other familiar structures like the pituitary gland here. Here's the brain stem and even this beautiful cerebellum over here. But the hypothalamus is involved with maintaining homeostasis throughout the body. But how does it do this? Well, for one, the hypothalamus is the principal autonomic center of the brain. And if you haven't heard of the autonomic division of the nervous system before, this is the part of the nervous system that controls unconscious processes. Like, it controls things automatically so you don't have to think about it. And the hypothalamus, being the principal autonomic center of the brain, controls many of these processes such as regulating certain behaviors, regulating food cravings, so thirst and hunger mechanisms, and even gets involved in regulating body temperature and the circadian rhythm. The hypothalamus also releases its own hormones and regulates the release of hormones from the pituitary gland. And this is probably why women are a little bit more affected with migraines than men, due to the greater fluctuations in hormone release with the menstrual cycle. So if we kind of just take a step back and we compare the functions of the hypothalamus with some of the pre-monitory symptoms like fatigue, behavioral changes, food cravings, etc., you can see how this relationship between alterations in homeostatic controls could result in these various symptoms.
So, is there anything that a person could do during this pre-monitory phase or before that could influence their risk of getting a migraine? And the answer is yes. The data have shown that people with migraines, their brains tend to be a little bit more sensitive to certain stimuli. And they have gathered a whole bunch of data on certain environmental stimuli that could be potential migraine triggers. And this can be quite the long list. Some of these triggers are emotional stress, hormones, not eating, weather, sleep disturbances, even certain smells or odors, neck pain, alcohol, bright lights, smoke, certain types of food, even exercise, and even sexual activity. That last one was admittedly kind of a bummer, but luckily that list is from most common to least common. In the study that we're referencing here, only 5% of people reported that sex was a possible trigger. So you can all probably still participate in safe consensual activities. But moving on.
So, why do we care about all of this information during the premonitory phase? Well, remember, it can start up to 72 hours prior to the actual headache. And if you can get ahead and start treatment before the headache even starts, the outcomes are much better. So when migraine patients come into the clinic with me, I'll ask them if they can trace or track the previous three days, specifically the types of foods they were eating, what was their mood like, what were their sleep patterns like, and if they had any of these symptoms. And if they can gather this information, it can be quite useful for future migraines. Now, the problem is, who doesn't yawn on a daily basis? Who doesn't have some food cravings? So, tracking some of these symptoms can be challenging, but a lot of the times these migraine patients can actually get enough information to find their triggers and what their symptoms are during this premonitory phase.
The next phase of a migraine is the aura phase. Only about one-third of people with migraines experience this phase. But what is an actual aura? Well, an aura is a fully reversible neurological symptom that precedes or sometimes even accompanies the actual headache. And there are four types of auras that you can see in a migraine. The first and most common is the visual aura, which is spotted or blurred vision. Sometimes people will have little zigzag lines that'll come into their visual field. This is the type of aura that I've had during my migraines, and mine completely precedes the headache and goes away prior to the headache starting. But this is one of my biggest warning signs to hurry and go get the migraine medications because again, the sooner you initiate treatment for migraines, the better the outcome. Some people can also get a sensory aura, which is tingling on one side of the body, typically in the upper limb or on a side of the face. You can get a language aura, which is difficulty with wording and speech, and even a motor aura, which is weakness on one side of the body.
Now, the language and motor auras can be a bit scary for people, especially during the first time, because people may think that these are similar to stroke symptoms. But a couple of things to keep in mind is that these are by far the least common types of migraine auras. And one main difference between these types of auras and stroke symptoms is that stroke symptoms tend to come on suddenly. Whereas the language and motor auras are more of a gradual onset over 20 to 30 minutes. But don't mess around. If you haven't been diagnosed with migraines before, if you experience these types of symptoms, get checked out at the emergency department immediately.
But what is responsible for the aura phase? Well, the going theory or going hypothesis is that there's this process called cortical spreading depression. And so let's use this brain to help us break down this term and to understand what's happening with this cortical spreading depression. What I'm tracing here is the largest portion of your brain called the cerebrum. Down here we have the cerebellum, but right here, the largest portion is called the cerebrum. And the outside surface of an organ is called the cortex. And so the outside surface of the cerebrum is referred to as the cerebral cortex. So that is what the cortical part is referring to with cortical spreading depression. But what is meant by the spreading depression part? Well, it's believed that there's this depression of neurons that occurs throughout the cortex, or this wave of neuronal depression that's propagating or spreading across the cerebral cortex. Kind of like a drop in a pond creating this ripple effect. Now, when a neuron depolarizes, that is essentially when it fires or sends its signal. But in this case, you get this wave of neurons depolarizing again across the cortex. And after this wave of neuronal depolarization takes place, the neurons tend to stay depolarized longer than they normally would before repolarizing or recharging. So, kind of remain in this depressed state, hence cortical spreading depression. And it's believed that this is responsible for the aura symptoms that we just previously mentioned.
Now, many people that get migraines don't get the aura. So, is this cortical spreading depression just not occurring in them? Well, that's not fully understood, and it still may be occurring. And if it is, it is either thought to occur in areas of the brain that are not under conscious awareness, or it may just be mild enough to where it doesn't create any noticeable symptoms in that person.
And now on to the third stage of a migraine, which is the actual headache phase. Now, this headache is characterized by a pulsatile throbbing pain that tends to be unilateral or one-sided. Some people will get it on both sides of the head and even sometimes on the back of the head, but most commonly it's one-sided. Now, a lot of people will also experience nausea, vomiting, photophobia, which again is light sensitivity, phonophobia, sound sensitivity, and even some people get sensitive to smells. Few people will get something called cutaneous allodynia, which is sensitivity to touch. Like the skin just gets hypersensitive, and just even touching a certain area of the skin will cause pain.
But what is the cause of all this miserable pain? Well, remember, this was preceded by the pre-monitory phase and the aura phase with cortical spreading depression. And it's thought that these previous phases activate the trigeminal vascular system. Now, some of you may have heard of the trigeminal nerve before, and this nerve gets activated during a migraine, and this is going to explain the cause of the migraine pain and even help us understand the location. The trigeminal nerve originates on the brain stem and then gives rise to three main branches, hence the prefix "tri." And I'll first show you these branches inside the skull. You have the ophthalmic division, the maxillary division, and the mandibular division. And these got named as such because they will leave the skull and then flare out onto the face. The ophthalmic nerve, which refers to the eye, goes to the forehead and around the eye. The maxillary nerve goes to the area of the maxilla or around the cheek. And the mandibular nerve goes to the area of the mandible. Now, this nerve is sometimes nicknamed the great sensory nerve of the face because if you were to touch anywhere on your face, all of that sensation is brought into the brain through the trigeminal nerve.
Now, that is part of this story of helping us understand migraine pain and its location, but there's also some internal structures that play a role in the pain of a migraine. And this is a really cool dissection that I'm about to show you. So, here you can see we're taking a look at the top left side of the head. And as you can see, I can remove the scalp. You can take a look at the underside there. I can also remove the skull. You can look at that inside surface there. And then underneath, you can see this connective tissue layer called the dura mater. And of course, we might as well show you the brain underneath. And as you can see, we obviously removed part of the frontal lobe there. But coming back to this dura mater. The dura mater surrounds and protects the brain. And it does have sensation. Specifically, it can sense pain. And guess what nerve brings in this pain sensation? The trigeminal nerve. And so when the trigeminal nerve gets activated during a migraine, it can also sensitize the pain receptors called nociceptors in the dura mater, and that signal will then come into the brain as a pain signal.
So now that we know the origin of the pain coming in from the dura mater through the trigeminal nerve and into the brain, we kind of have to answer, well, why do I feel pain around the eye or the forehead, or in some people in the back of the head, when the stimulus is essentially coming from the pain receptors in the dura mater that is inside the skull? Well, that's a story of referred pain. And to describe referred pain, we have to describe neurons converging into similar places of the brain. So, for example, if I have a sensory neuron on my forehead that runs through the ophthalmic nerve branch of the trigeminal nerve, but then I also have a neuron coming in from the dura, which is deeper inside the skull, but these are converging on a similar nucleus inside the brain. That sometimes tricks the brain into thinking, "Oh, the pain's coming from here on my forehead and around the eye rather than this deeper structure that I hardly ever get pain signals from." And for someone that experiences migraine pain in the back of the head rather than on the front of the head, that would just be maybe a different area of the dura that is getting sensitized, and that neuron that's bringing in the pain signal from that part of the dura is converging with a neuron that comes from another area like on the back of the head, than as opposed to say, like a neuron that's on the front of the head.
But this finally gets us to the final stage of a migraine. The last phase of a migraine is called the postdrome phase, and that is essentially lingering symptoms from the migraine. Now, migraines can be quite debilitating during that pain phase because it's just this relentless pulsatile pain that just hurts so bad. But people also notice that it even can hurt just to turn their head, sneeze, cough, and bend over. And the next day after a migraine, a lot of people will realize, "Oh, I still have some of that pain or that residual pain of when I turn my head quickly or when I cough or when I sneeze." And the reason for this is something called sensitization. The nerve that we just talked about, the trigeminal nerve, and those tissues, those sensory nerve fibers and nociceptors essentially get sensitized to stimuli that normally wouldn't cause pain. And so again, this explains why when you turn your head, it can hurt, or when you sneeze or when you cough, it can hurt that day after a migraine. But luckily, this sensitization typically goes away over the next day or so. And hopefully, you're going to have a huge gap of time between this postdrome phase and your next pre-monitory phase, aka the beginning of your next migraine, which I would never wish upon anyone.
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