Though BAM is a migraine variant, and therefore technically belongs under the classification of "migraine," a BAM attack can also represent a form of "acute cerebral vascular insufficiency." The other forms of migraine variant are (1) retinal migraine, (2) opthalmoplegic migraine, (3) hemiplegic migraine, (4) facial migraine, and (5) migrainous infarction.

Of these, only hemiplegic migraine has been found to be a dominant characteristic in terms of heritability in families. Hemiplegic migraine is also the only form of migraine for which a gene has been located. It is a gene located on chromosome 19 that carries the trait for hemiplegic migraine. Hemiplegia can develop either before or during a migraine. Though Basilar Artery Migraine is certainly a distinct form of migraine variant, BAM patients can exhibit the signs of hemiplegic migraine.

The last category of migraine variants listed above, that of migrainous infarction, deserves special note when discussing BAM.

BAM and Other Migraine Classifications

In very simple terms, migraines can be divided into two broad classes: common migraine and classic migraine. The common migraine, of which there are several forms, does not normally have what is called an "aura." Classic migraines, however, do have this aura. In fact, they are also sometimes referred to as, simply, "migraine with aura." Conversely, common migraine may also be referred to as "migraine without aura." A rough estimate is that about 80% of all migraines are common migraines, leaving the other 20% as classic migraines.

BAM is a variant of classic migraine, as it has an aura. However, it is quite different from most classic migraines in how it manifests itself and its other clinical aspects.

Migraine Aura Without Headache

Migraine aura without headache (formerly called migraine equivalent or acephalic migraine) refers to visual, neurologic, or gastrointestinal symptoms occurring transiently and without headache. These symptoms occur in persons who have had previous migraines, or who have a family history of migraine. In some cases, they can also occur in people who have never had migraines.