The
exact source of the migraine has been somewhat controversial. The old theory,
put forward by Dr. Wolff is that vasodilatation (enlarging) arteries cause
the headache pain that was associated by migraine and presumably the throbbing
nature of the headache was the pulse. He based his belief on a number of
factors including:
- Observation of an individual migraine patient who, because of a prior brain injury, had a hole in her skull. The hole would become depressed prior to a migraine and then would enlarge during the migraine headache. The shift in size was felt to be induced by blood flow changes.
- That manual pressure on the arteries to the brain during the headache reduced the pain. Don’t try this at home.
- That vasoconstrictors (drugs which make the arteries smaller) reduce migraine headaches.
- That injections of some vasodilators caused migraine.
- That manipulation of the temporal artery in some migraine patients reproduce their migraine.
Given the testing available during the time of his work, Dr. Wolff’s theories were rapidly accepted. They are, however, probably not the cause of migraine or at least, only a partial explanation of what is happening during the migraine headache.
Dr. Mike Moskowitz has performed most of the groundbreaking work for the neurogenic theory of migraine and the information presented here is summarized from a number of his articles and lectures. If one looks at the nerve supply to the pain sensitive structures in the head (dura, venous structures, etc), they are innervated by a meshwork of nerves that are mostly from the first division of the trigeminal nerve. Each nerve goes to a wide area of the dura but in general, the nerves do not cross the midline. These nerves are interwoven around the blood vessels and are closely associated with mast cells. In the brain, the cells of the trigeminal nerve project to centers in the brain stem as well as areas of the brain responsible for nausea. On your skin, the first division of the trigeminal nerve is responsible for sensation from an area above your eye through the top of your head. During a migraine, these axons release substances that cause blood vessels to vasodilate and nearby mast cells to release additional substances that trigger pain and also cause blood vessels to vasodilate. Some substances cause the vessels to leak fluid and an inflammatory reaction to occur and the entire process is described as neurogenic inflammation. Some substances are also felt to make the blood vessel wall area more sensitive to previously innocuous stimulus such as the mechanical distention of the pulse. Because the nerves transmitting the pain signals from the affected area also supply sensation to the area above the eye, the pain is referred to the temporal or forehead region.
Migraine Source |
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