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Tuesday, January 17, 2012

The GUIDE: Migraine

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Oh.  The PAIN!

Headaches occur at a minimum of once per week in persons living in industrialized society.  They can be simply a slight pain induced by too much reading, polluted (or stale) air, food triggers, not enough sleep or allergic reaction.  It is tempting to refer to all severe headaches as "Migraines", especially if they occur with regularity.  However, not all headaches are migraines, and not all migraines are the same.

Let's start with some definitions and descriptions.  First, headaches are really neural in that they don't mean that the cells of the brain are acting in any manner different from normal.  Instead, headaches are a vascular problem.  Metabolic imbalances cause tiny blood vessels to expand, the increased blood flow causes changes in other blood vessels and in brain activity.  In addition, there is release of the neurotransmitter serotonin, and its close chemical sibling: histamine.  Those chemicals cause further reaction of the blood vessels, leading to the sensations we know as a headache.

The involvement of histamine means that there are many ways of triggering headaches - sinus congestion, allergy, food reactions, excess carbon dioxide in the atmosphere, etc.  The CO2 involvement is one reason why breathing oxygen relieves headaches - high CO2 causes blood vessels to dilate (get larger) increasing blood flow in the brain to higher than normal levels, while high O2, low CO2 causes those same vessels to constrict and reduce blood flow to normal levels.

video
All of these causative factors lead to the same sensation: discomfort and perceived pressure in the forehead area, behind the eyes.  The brain itself does not have the nerve endings that signal pain in the rest of the body, so the sensation of pain is really one of pressure, and it results from the "cognitive" areas of the brain trying to find a way to represent the chemical changes that result from the unusual blood flow patterns.

Migraine starts the same way, but adds a new components, because migraines really do involve a change in the electrical activity of the brain.  To start with, the majority of migraine sufferers report a "prodrome" or "aura" before the pain sets in.  This aura is quite frequently associated with visual changes - light sensitivity, flashing, pulsing, tunnel vision, blurring, spots or even temporary blindness.  In this manner, the aura of a migraine is quite similar to that preceding an epileptic seizure (see prior blogs on Seizures and Epilepsy), but is most often visual and does not spread or involve other senses.  The aura signals the initial "irritation" of the blood vessels that supply the brain, but the migraine pain itself comes from the later reaction in which neuron activity is suppressed by what is called "spreading cortical depression."  No, this doesn't mean depression in the clinical sense, but that brain activity is in fact suppressed and only the strongest (and most noticeable) signals can be processed.  The video above illustrates the spreading depression in the orange band that starts in the visual cortex and spreads up and forward to include the Parietal, and even the Frontal Lobes of the brain.

The interesting parallels between migraine and seizure continue, but migraines are not epileptic in nature.  Seizures do involve some element of cortical depression, reduction in normal brain activity is necessary to set up the abnormal synchronous activity of an epileptic seizure.  After the seizure passes, there can be spreading cortical depression.  However, the synchronous activity does not occur in migraine, only the spreading depression, and that appears to result from the serotonin and histamine release from the cells lining the blood vessels.  Still, some seizure medicines (sumatriptan - Imitrex) can be useful in treating migraines in that they can limit the spreading cortical depression by altering neural response to serotonin.  Preventative medication for migraines often involves blood pressure/calcium blocker medicines such as Verapamil that can reduce the "irritation" of blood vessels.  Injection of very small amounts of botulinum toxin (Botox) into the blood vessels that most frequently react to induction of a migraine can also reduce the "irritability" and reduce the frequency of migraines. 

Migraines typically last from 4-72 hours and are accompanied by extreme light sensitivity, nausea, blurred vision, fatigue, hypersensitivity to sound and yes - short-term psychological depression.  However, it is very easy to call any severe headache a "migraine" even when that is not the case.  Allergic rhinitis - i.e. a "stuffy nose" and sinus congestion can trigger headaches that react to pressure in the sinus cavities that surround the nose and sit adjacent to the olfactory bulb - the "smell" center of the brain.  The proximity of sinus to the Frontal Lobe means the pressure gets translated to the brain, and the neurons react with activity that signals pain.

And yet, migraines may very well have an allergic component.  A well-known trigger for migraine is certain foods and food additives.  Nitrites in cooked/preserved meats, artificial coloring agents, phenylalanine in artificial sweetener, food allergens such as tomato or nuts, and surprisingly - yeast breads.  The reason is because any trace of food allergy (or mold allergy, in the case of yeast) can cause the histamine increase leading to migraine.

I did mention, though, that not all "migraines" are in fact the classic migraine described here.  "Cluster headaches" - so named because the headaches occur in "clusters" that frequently occur at the same time each day, with pain in the same area of face and/or head, and occur for weeks or even months at a time -  vary from migraines and conventional headaches because it appears that they *do* involve some unusual brain cell activity.  Cluster headaches are not preceded by auras, and the pain is quite often confined to one side of the face and head.  They are still treated with some of the same drugs as headaches and migraines, as well as a few specific drugs to disrupt the activity of the neurons that trigger the headache.  If these treatment options fail, the docs need to take a look inside the head - not to see if there is anything missing, but to look for unusual blood vessel formation or something that might be causing pressure.

Headache is all about blood pressure and blood flow, since this Guide is all about brain disorders at plot devices, it is important to consider what could cause headaches and migraines to stop or start - and that comes down to anything that disrupts blood flow.  Physical head injury, hormonal changes (puberty, pregnancy, menopause), blood loss, allergy, surgery - all of these could trigger the onset, or mark the cessation of a lifetime of headaches.  Don't forget the debilitating effects - imagine if during his Labours, Hercules had needed go lie down for 3 days to allow a migraine to pass!  Then again, a headache-ridden Theseus may have welcomed the dark and dank Labyrinth and slain the minotaur if only for access to a refuge from sun and sea!

Tomorrow, to complement this blog will be a short article on pain medication.  Thanks for reading!

- s2la 

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