Understanding Migraine Disease

In the last few decades, research about migraine headaches has come a long way.For example, a migraine headache is now believed to be a symptom of a morecomplex disorder, migraine disease. A number of theories have been proposed toexplain the cause of our disease. Let's take a look at some of them.

The Vascular Theory

For much of my life, medical researchers believed migraine was a headacherelated to changes in the blood vessels in and around our brains. When exposedto triggers, which I explained in the Introduction as events capable ofprovoking our migraine attacks, our arteries narrowed. This constriction reducedblood flow and oxygen delivery to our tissues. As our constricted arteriesexpanded and tried to gain more oxygen, fluid leaked into the surrounding tissueand chemicals such as prostaglandin, which enhances the sensitivity of painendings and stimulates the release of inflammatory agents, were released. Thiswas known as the vascular theory.

Recent Theories

Recent theories suggest that migraine is a neurological disease, which involvesmore than dilation and constriction of blood vessels. Evidence suggests we havean inherited disruption in brain function that makes our brain cells moreexcitable than others. When exposed to triggers capable of provoking a migraineattack, a chemical imbalance occurs in our brains. Levels of neurotransmitters(chemical messengers that pass information from one cell to another), such asglutamate, serotonin, dopamine, and norepinephrine, are altered. The most recenttheories implicate one or more of these neurotransmitters as culprits in ourdisease. So, what are these recent theories?

Cortical Spreading Depression Theory

The cortical spreading depression theory believes that a wave ofhyperexcitability spreads across the outer layer of our brain (the cortex),followed by a period of suppression. When brain activity is depressed,inflammatory mediators are released. These inflammatory mediators irritate thecranial nerve roots, in particular the trigeminal nerve, which conveys sensoryinformation for much of our head and face.

Glutamate, a neurotransmitter present in the trigeminal nerve, is thought toplay a role in the cortical spreading depression. As well, a neurotransmitterfound in the brain and spinal cord and known as substance P is thought tocoexist with glutamate. Substance P is believed to be involved with theinflammatory process, vasodilation, smooth muscle contraction, nausea andvomiting, regulation of mood disorders such as anxiety, and the sensation ofpain.

The Serotonin Theory

Serotonin, also known as hydroxytryptamine or 5-HT, is believed to have a majorrole in migraine disease. The serotonin theory suggests that we have a defect ina specific type of serotonin receptor that causes our blood vessels toconstrict, or narrow. As a result, in the presence of certain triggers, arteriesthat supply blood to our brain dilate, or expand. The dilation, or stretching,of the arteries in and around our brain causes fluid to leak into surroundingtissue. The fluid leak damages tissue cells and stimulates the release ofinflammatory agents, which contribute to the swelling of the arteries andsurrounding tissue, leads to irritation of nerves, and intensifies our throbbingpain. Also, because serotonin enhances endorphins (a natural analgesic found inthe gray matter of the brain) and has an effect on substance P, low levels ofserotonin further exacerbate our pain.

Besides alterations in cerebral blood flow and the sensation of pain, changes inthe levels of serotonin are thought to be responsible for a number ofgastrointestinal symptoms such as nausea, vomiting, and diarrhea that many of usexperience during an attack. This is because serotonin is also aneurotransmitter for the enteric nervous system, or ENS, which is located in theabdomen (ninety-five percent of the body's serotonin is located in the gut).Often referred to as the second brain or gut brain, the ENS causes contractionof the smooth muscle of the gut that is important for normal digestion and themovement of food through the intestines (peristalsis). As well, it regulatesintestinal blood flow, the transport of mucosal water and electrolytes, andpropulsive bowel function.

Blood levels of dopamine and norepinephrine are believed to fluctuate with ourserotonin levels. All three of these neurotransmitters may be responsible formany of the other symptoms we exhibit as our migraine attack progresses. Forinstance, high levels of serotonin may make us feel calm, full, relaxed, andeven drowsy. Low levels may cause us to feel anxious, irritable, and depressed.They may also promote food cravings for starches and sugars, like crackers,chips, ice cream, and chocolate.

An increase in dopamine and norepinephrine levels may make us feel moreenergetic, focused, and alert. A decrease in these levels may contribute to thefatigue, inability to concentrate, yawning, nausea, and vomiting many of usexperience.

The Integrated, or Unifying, Theory

The integrated or unifying theory suggests that both vascular and neuralinfluences cause the pain associated with migraine headaches. This theorysuggests that stress and other triggers cause changes in the levels ofepinephrine in our bodies, which affects serotonin levels. Fluctuations inserotonin levels cause blood vessels to constrict and dilate. Chemicals, such assubstance P, are released and further irritate nerves and blood vessels andenhance our pain and inflammation.

Defining Migraine Disease

The organization MAGNUM (Migraine Awareness Group: A National Understanding forMigraineurs) refers to migraine as an organic neurological disease. Although theimportance of the role of one theory over another is debatable in theliterature, the disease itself seems to be related to a complex series of eventsthat results in a breakdown of communication between the neurotransmitters inour brain and, as more recent research suggests, in our gut. When exposed tocontrollable or uncontrollable triggers, which you read about in Chapter Three,a chain reaction is initiated that sets off a cascade of events referred to as amigraine attack.

What Is a Migraine Attack?

A migraine attack is the episodic event we endure in the presence of anappropriate trigger. The attack has been split into four phases: the...