migraine aura

   The term migraine comes from the Old English megrim, which is in turn indebted to the Greek noun hèmikranion (meaning half the skull). The introduction of the term hèmikranion is attributed to the classical physician Galen of Pergamum, born as Claudius Galenus (129-c. AD 216). Today migraine is conceptualized as a primary neurological syndrome, typically (although not invariably) responsible for a moderate to severe unilateral headache with a pulsating quality, which may be accompanied by symptoms such as nausea, vomiting, *photophobia, and *hyperacusis. The term * aura is Greek for wind or smell. The term migraine aura is used to denote any neurological sign or symptom that may accompany either the development phase of a migraine attack or the migraine attack itself. It may or may not be followed by a migraine headache. An early description of a visual migraine aura can be found in the Hippocratic Corpus, written around 400 BC. A migraine aura occurs in 10-40% of all individuals acquainted with migraine. As migraine itself has a lifetime prevalence of 12-28%, it has been suggested that the visual migraine aura constitutes the most prevalent type of visual hallucination. The two most prevalent variants of migraine with visual aura are called migraine with aura (the approved term of the World Federation of Neurology for what was formerly known as classic migraine) and migraine aura without headache (formerly known as migraine accompagnée and acephalgic migraine). The spectrum of neurological signs and symptoms that may occur in the context of a migraine aura includes * phosphenes, coloured *photopsia patterns, * fortification spectra (also referred to as positive visual aurae), *scotomata, *quadrantanopsia, * hemianopia, tunnel vision, *amaurosis fugax (also referred to as a negative visual aura), ophthalmoplegia, oculosympathetic palsy, * diplopia, monocular crescent, mydriasis, digito-lingual or cheiro-oral *paraesthesias, heaviness of the limbs, hemiparesis, vertigo, difficulty reading or writing, aphasia, dysphasia, dysarthria, and brain stem symptoms. In addition, various types of *metamorphopsia may occur, such as *dysmegalopsia, *macroproxiopia, *microtelepsia, *pelopsia, *micropsia, and *macropsia. Relatively rare phenomena occurring in the context of migraine aura are * macro- and * microsomatognosia, in which one's own body, in part or in whole, is perceived as being dispropor-tionally large or small. These metamorphoptic symptoms may cluster in such a way that they fulfil the criteria of the * Alice in Wonderland syndrome. In the context of the migraine aura, complex visual hallucinations have also been reported, including * lilliputian and * gulliverian hallucinations. The migraine aura tends to appear gradually over 5-20 min, and to last no longer than 60 min. There are many types and patterns of visual aura, but many of these start with the homonymous appearance of fortification spectra, which then surround or define an area of scotomatous visual loss (also referred to as a scintillating positive scotoma). These scotomata may be bordered by coloured photopsia patterns. Scotomata often move from an area adjacent to the fixation point out to the periphery. The temporal sequences of signs and symptoms in migraine aura are referred to as a 'march'. They are indicative of an underlying spreading disturbance of cerebral cortical areas, typically at a speed of 2-3 mm/min. The concomitant concept, called the spreading depression concept, was developed in or shortly before 1944 by the Brazilian biologist Aristides Azevedo Pacheco Leâo (1914-1993). A competing concept, referred to as the vascular concept, was developed by the American biologist and philosopher Harold George Wolff (1898-1962). Various clinical and experimental findings support the vascular concept, especially as regards the quality of the pain characteristic of the migraine headache. And yet the spreading depression concept would seem to be better equipped to explain the creeping, epileptiform patterns of cerebral dysfunction characteristic of the migraine aura. In an effort to combine the strengths of both concepts, some authors have advocated what they call a unification theory of the migraine aura.

   References

   Amos, J.F. (1999). Differential diagnosis of common etiologies of photopsia. Journal of the American Optometric Association, 70, 485-504.

   Lauritzen, M. (1994). Pathophysiology of the migraine aura. The spreading depression theory. Brain, 117, 199-210.

   Leâo, A.P.P. (1944). Spreading depression of activity in the cerebral cortex. Journal of Neu-rophysiology, 7, 359-390.

   Morrison, D.P. (1990). Abnormal perceptual experiences in migraine. Cephalalgia, 10, 273-277.

   Rubin, D., McAbee, G.N., Feldman-Winter, L.B. (2002). Auditory hallucinations associated with migraine. Headache, 42, 646-648.

   Schott, G.D. (2007). Exploring the visual hallucinations of migraine aura: The tacit contribution of illustration. Brain, 130, 1690-1703.

   Wilkinson, F. (2004). Auras and other hallucinations: Windows onthevisual brain. Progress in Brain Research, 144, 305-320.