But Where Does a Migraine Come From?

by Food and Drug Administration (FDA)

(Page 2 of 4)

A longstanding theory holds that blood vessels in the scalp and on the brain's surface constrict. This reduces the brain's oxygen supply to produce the aura some patients have. The same vessels, reacting to the brain's need for oxygen, open up, or dilate, releasing pain-causing chemicals called prostaglandins, other chemicals that increase sensitivity to pain, and still others that induce painful inflammation and swelling.

Stark is among the neurologists who subscribe to a newer theory that migraine stems from a chemical change deep within the brain, where the body uses the neurotransmitter serotonin abnormally. (Neurotransmitters are chemical messengers that nerve cells use to tell each other what to do.)

Working with other chemicals, serotonin regulates blood vessel constriction and dilation. It can both sharpen and deaden pain. While serotonin's role in migraine isn't completely understood, areas of the brain responsive to serotonin are often involved in migraine. The hypothalamus, for instance — which regulates involuntary bodily functions such as menstruation, sleep and hunger — has cells sensitive to serotonin. Such cells also appear in large amounts in the stomach and intestinal walls. Certain serotonin cells stop "firing" during sleep, which often ends a migraine attack.

"Serotonin acts on the electrical impulses sent out by nerve cells in and around the blood vessels in the brain," Stark explains. "We believe that in a migraine attack, the serotonin isn't properly used for some reason, so that the electrical wave of impulses becomes diminished, or depressed. The wave, called 'spreading depression,' reduces blood flow through the vessels leading to the back of the brain.

"This is when the aura occurs. The symptoms depend on which areas of the brain are included in the wave. Spreading depression is believed present in all migraine attacks, even in people who don't have auras.

"After the spreading depression subsides, the blood vessels start leaking fluid, inflaming the outside of the vessels. The inflammation causes the pain, which can extend to all the nerve cells supplying the blood vessels, not just those in the area of the spreading depression."

The spreading depression correlates with the aura, but not the headache, Stark says. In other words, a depressed wave limited to one side of the head can lead to pain on both sides.

Also, some scientists believe a disturbance in the brain's trigeminal nerve contributes to migraine headache by causing the release of "substance P," which causes inflammation.

If these theories are correct, changes in the head's blood vessels, impulses deep within the brain, and the pain pathway in the trigeminal nerve may all play a part in migraine pain.

Given the theory that most migraineurs are predisposed to their condition, migraine has been described as a cocked gun waiting to go off — except that this gun has many triggers.

A trigger for Bailey was cigarette smoke. "At a party where lots of people were smoking and there wasn't good air flow, I'd nearly always get sick," she says. "Once I was sick, smells such as glue, pesticides or perfume egged it on."

Reaction to stress is a common trigger. Others include fatigue, lack of sleep, glaring lights, excessive noise, weather, certain drugs that cause blood vessels to swell, and hormonal fluctuation — as happens around menstruation, at menopause, and during use of birth control pills.

Foods trigger migraines, too. Keeping a food diary can help identify sensitivities.

As for headache prevention and treatment, FDA has approved a number of anti-migraine drugs. Their benefits vary from person to person and must be weighed against the risks, some of which are serious.

"One preventive drug is Inderal [propranolol]," says FDA's Katz. "It was initially approved to treat high blood pressure and heart problems, and only accidentally found to prevent migraine. It's not useful after the headache begins." FDA approved Inderal, a beta blocker, for preventing migraine in 1979. It's the only beta blocker with this indication. Inderal's effect in migraine is not well-understood.

The other drug approved for preventing migraine is Sansert (methysergide), one of several ergot drugs, which constrict blood vessels. Sansert can't be given continuously for more than six months, so its use is limited.

"Effective drugs to stop a particular attack of migraine once it has started," Katz says, "include analgesics and ergotamines. Whichever is used, it must be taken early in the attack to be most effective." For occasional mild migraines, he says, over-the-counter pain relievers or prescription drugs with a low dose of codeine are usually adequate.

"Isometheptene combined with dichloralphenazone and acetaminophen — Midrin or Isocom — may also be helpful early in an attack," Katz says. "Anti-emetics can relieve the associated nausea and vomiting in migraine."

OTC analgesics approved for headache include aspirin, Tylenol (and other brands of acetaminophen), and Advil, Motrin IB, and Nuprin (and other brands of ibuprofen). Ergot drugs include Ergomar, Ergostat, Cafergot, Wigraine, and D.H.E. 45.

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.