Migraines were once thought to be initiated exclusively by problems with blood vessels. The vascular theory of migraines is now considered secondary to brain dysfunction and claimed to have been discredited by others. Trigger points can be at least part of the cause, and perpetuate most kinds of headaches.
The effects of migraine may persist for some days after the main headache has ended. Many sufferers report a sore feeling in the area where the migraine was, and some report impaired thinking for a few days after the headache has passed.
Migraine headaches can be a symptom of Hypothyroidism.
A phenomenon known as cortical spreading depression can cause migraines. In cortical spreading depression, neurological activity is depressed over an area of the cortex of the brain. This situation results in the release of inflammatory mediators leading to irritation of cranial nerve roots, most particularly the trigeminal nerve, which conveys the sensory information for the face and much of the head.
This view is supported by neuroimaging techniques, which appear to show that migraine is primarily a disorder of the brain (neurological), not of the blood vessels (vascular). A spreading depolarization (electrical change) may begin 24 hours before the attack, with onset of the headache occurring around the time when the largest area of the brain is depolarized. A French study in 2007, using the Positron Emission Tomography (PET) technique identified the hypothalamus as being critically involved in the early stages.
Migraines can begin when blood vessels in the brain contract and expand inappropriately. This may start in the occipital lobe, in the back of the brain, as arteries spasm. The reduced flow of blood from the occipital lobe triggers the aura that some individuals who have migraines experience because the visual cortex is in the occipital area.
Serotonin is a type of neurotransmitter, or "communication chemical" which passes messages between nerve cells. It helps to control mood, pain sensation, sexual behaviour, sleep, as well as dilation and constriction of the blood vessels among other things. Low serotonin levels in the brain may lead to a process of constriction and dilation of the blood vessels which trigger a migraine. Another study of 10 patients with a long history of chronic headaches that had recently worsened or were resistant to treatment found that all 10 patients were sensitive to gluten. MRI scans determined that each had inflammation in their central nervous systems caused by gluten-sensitivity. Seven out of nine of these patients that went on a gluten-free diet stopped having headaches completely.
While some people believe that aspartame triggers migraines, and anecdotal evidence is present, this has not been medically proven. However another trial found no effect when 3.5g of MSG was given with food.
The National Headache Foundation has a specific list of triggers based on the tyramine theory, detailing allowed, with caution and avoid triggers. However, a 2003 review article concluded that there was no scientific evidence for an effect of tyramine on migraine.
A 2005 literature review found that the available information about dietary trigger factors relies mostly on the subjective assessments of patients. Some suspected dietary trigger factors appear to genuinely promote or precipitate migraine episodes, but many other suspected dietary triggers have never been demonstrated to trigger migraines. The review authors found that alcohol, caffeine withdrawal, and missing meals are the most important dietary migraine precipitants, that dehydration deserved more attention, and that some patients report sensitivity to red wine. Little or no evidence associated notorious suspected triggers like chocolate, cheese, histamine, tyramine, nitrates, or nitrites with migraines. However, the review authors also note that while general dietary restriction has not been demonstrated to be an effective migraine therapy, it is beneficial for the individual to avoid what has been a definite cause of the migraine.
Several studies have found some migraines are triggered by changes in weather. One study noted 62% of the subjects thought weather was a factor but only 51% were sensitive to weather changes. Among those whose migraines did occur during a change in weather, the subjects often picked a weather change other than the actual weather data recorded. Most likely to trigger a migraine were, in order:
- Temperature mixed with humidity. High humidity plus high or low temperature was the biggest cause.
- Significant changes in weather
- Changes in barometric pressure
Another study examined the effects of warm chinook winds on migraines, with many patients reporting increased incidence of migraines immediately before and/or during the chinook winds. The number of people reporting migrainous episodes during the chinook winds was higher on high-wind chinook days. The probable cause was thought to be an increase in positive ions in the air.
One study found that for some migraineurs in India, washing hair in a bath was a migraine trigger. The triggering effect also had to do with how the hair was later dried.
Strong fragrances have also been identified as potential triggers, and some sufferers report an increased sensitivity to scent as an aura effect.
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