A rare but severe form of migraine that causes temporary paralysis-sometimes lasting several days-on one side of the body prior to or during a headache. Symptoms such as vertigo, a pricking or stabbing sensation, and problems seeing, speaking, or swallowing may begin prior to the headache pain and usually stop shortly thereafter. When it runs in families the disorder is called Familial Hemiplegic Migraine (FHM). Though rare, at least three distinct genetic forms of FHM have been identified. These genetic mutations make the brain more sensitive or excitable, most likely by increasing brain levels of a chemical called glutamate.
It has been shown that FHM very often has basilar-type symptoms in addition to the typical aura symptoms and that headache is virtually always present. During FHM attacks, disturbances of consciousness (sometimes including coma), fever, CSF pleocytosis and confusion can occur. FHM1 attacks can be triggered by (mild) head trauma. In approximately 50% of FHM1 families, chronic progressive cerebellar ataxia occurs independently of the migraine attacks. FHM is very often mistaken for epilepsy, and (unsuccessfully) treated as such.