Introduction to the Physiology of BAM

The physiology of Basilar Artery Migraine is somewhat unique, and the condition is often difficult to diagnose. Basilar Artery Migraines are a complicated phenomenon involving biochemical, neurogenic, and vascular components.

Persons with Basilar Artery Migraine can exhibit symptoms also found in other neurological disorders such as stroke or epilepsy. Patients' reports of Basilar Artery Migraine symptoms, especially in severe cases, can prompt the often arduous process of differential diagnosis to rule out conditions like epilepsy, stroke (cerebral infarct), brain tumor, aneurysm, or other neurological conditions.

What Causes Basilar Artery Migraine

The Direct Causes of BAM

BAM is a result of vasospasm (spasm of the artery or vessel) or vasoconstriction (constriction or narrowing of the artery or vessel) in the area of the vertebrobasilar circulation, most likely usually in the basilar artery itself.

Spasm or constriction in the basilar artery necessarily affects the circulation of blood in the entire vertebrobasilar region, as the basilar artery itself is key to providing circulation to the posterior areas of the brain. BAM is a migraine variant that involves ischemia (lack of sufficient blood supply) to parts of the brain supplied by the vertebrobasilar circulatory system.

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Relationship to Familial Hemiplegic Migraine

Basilar Artery Migraine may have certain pathophysiologic mechanisms in common with a neurological disorder known as "familial hemiplegic migraine." Both BAM and familial hemiplegic migraine may consist of a genetically determined "disturbance" of the blood flow in and through the basilar artery and surrounding territory.

Possible Indirect Causes of BAM

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Neurochemical

Thrombolytic

Congenital

Physical Damage

Acute Trauma

Other Possible Factors Involved in BAM

The Possible Role of Serotonin

The Causes of Migraines

Despite their prevalence, nobody really knows with certainty all of the reasons why migraine occurs. There are various theories, and some factors that may play a part in migraine have been identified. Some of these factors are family history (a genetic component to migraine propensity), changes in regional blood circulation in the brain, "hyperexcitability" of the trigeminal nerve, head injury, tension, stress, vascular abnormalities, imbalance in the levels of various neurotransmitters in the brain, etc. Most scientists would agree that the origin of migraine attacks is in the brain itself, although the exact mechanisms still remain somewhat of a mystery..

There is considerable medical evidence to suggest that migraine is caused by electrical and/or chemical instabilities in the brain, specifically instability of certain key neurotransmitters. Instability of certain neurotransmitters can also cause various seizure disorders. Such neurotransmitter imbalance problems seem to be inherited or have a genetic component. It is thought that the neurotransmitter called serotonin plays a crucial role in migraine.

Migraines and seizure disorders alike can often be successfully treated by medications that change the way the neurotransmitters work within the brain and the way they facilitate and moderate communication between the brain's nerve cells, or "neurons." These medications work by in effect "stabilizing the brain's chemistry."

Instability in brain chemistry may actually cause several different kinds of headaches, in addition to migraines. It used to be thought that migraine was caused by a painful swelling of the vessels within the brain, often following a constrictive phase during which those who suffer from classical migraine or migraine with aura actually experience the neurological signs associated with migrainous aura. However, we now know that, even though the constriction and/or dilation of vessels and arteries within the brain may very well play a part in migraine, this constriction and dilation is likely intricately tied in with the functioning of the brain's neurotransmitters--and the subsequent effects that neurotransmitter function and brain neurochemistry have upon the function of the vessels themselves.

In addition to various causes of migraine, it is important to note that there are also the common "triggers" that may play a role in bringing on an attack of common or classical migraine.

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Some Basic Neuroanatomy and Terminology Related to BAM

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The Intracranial Vascular System

The Basilar Artery

The basilar artery is about 1 inch long and is the only place in the body where two arteries join into one and then again separate. The two vertebral arteries (they run up the spine) go up the spine and the bottom part of the brainstem and then join along the brainstem to form the basilar artery. The basilar artery and its subsequent branches (the posterior cerebral arteries, etc.) are quite important in supplying blood to the posterior or back portion of the brain, and particularly to the brainstem itself. Though some blood supply can be "made up for" from the blood from the carotid arteries (going up the sides of the neck) being circulated through what they call the Circle of Willis and then being "sent" to other areas of the brain, BAM sufferers normally experience problems related to ischemia of the posterior portions of the brain and/or the brainstem.

More to come here... As a note, I will be contacting some medical and scientific sources to see if they have some image files they might be kind enough to let me use. These would include pictures of the brain, the basilar artery, the vertebrobasilar system, the Circle of Willis, the brainstem and its components, and the various lobes of the cerebral cortex.

The Vertebral Arteries

The Posterior Cerebral Arteries

The Carotid Arteries

The Circle of Willis

The Brain

The Brainstem

The Pons

The Medulla Oblongata

The Reticular Formation

The Cerebellum

The Occipital Lobe

The Cranial Nerves

Transient Ischemia as Part of BAM

Ischemia basically relates to lack of blood supply, where in this case (BAM), not enough blood is supplied to certain areas of the brain and those areas then have an inadequate supply of oxygen (which is normally supplied through the blood supply of the basilar artery). This ischemia can, if what they call the CBF (cerebral blood flow) levels drop too low for too long a time (it can be a different number of minutes, depending upon factors like temperature, blood sugar levels, etc.) lead to stroke, where the brain cells or "neurons" in the starved area begin to die off.

This ischemia, which in BAM is normally transient or temporary in nature, is often associated with a BAM attack. It is very much like the transient ischemia experienced by others who do not have BAM, though different areas of the brain may be involved. These ischemic attacks are called "TIAs" or "transient ischemic attacks," and are sometimes called "little strokes," though that's not really an accurate term. Stroke generally means permanent damage, whereas TIAs or ischemia do not necessarily imply such permanency.

Numbness can indeed be part of BAM, and is very often one of the most prominent symptoms of a TIA. BAM, though, can and often does, have a wide range of symptoms associated with it, the TIA and vision problems being just two of many. In fact, your providing the most detailed history of your symptoms, their duration, etc., is one of the most important things you can do to help your neurologist accurately diagnose you. Other diagnostic tools that are often used in arriving at the BAM diagnosis include CT Scans, MRIs (and/or MRI angiograms), EEGs, and possibly blood tests like ACA (anti-cardiolipin antibody).

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Why Taking Vasoconstrictors Can Be Dangerous

One critical consideration is that if you do have BAM, Imitrex or other vasoconstrictors can actually be helping to cause some of your episodes. A vasoconstrictor constricts the blood vessels.

If you have BAM, your problem is basically that the vessel is constricted and you have insufficient blood flow. If you take that and add further vasoconstrictive action, like from taking Imitrex, you can make the possibility of worse symptoms, more frequent attacks, stroke, coma, and other serious consequences much more likely. That is why I recommend you discuss it with a neurologist who is familiar with BAM. If you do have BAM, it is potentially very dangerous for you to take a vasoconstrictor.

This is something you might wish to discuss with a neurologist. There are several forms of treatment, other than vasoconstrictors, available for those who have Basilar Artery Migraine.

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Warning Against Imitrex for BAM Patients