Blau and Dexter and Drummond are confident that the presence or absence of headache does not depend solely on extracranial vascular factors. These authors point to their findings that occlusion of blood flow through the scalp or common carotid circulation fails to alleviate the pain of migraine in one-third to one-half the patients. Lance and Goadsby have has suggested that the trigeminal pathways are in a state of persistent hyperexcitability in the migraine patient and that they discharge periodically, perhaps in response to hypothalamic stimulus acting on the endogenous pain control pathways. This is in keeping with current theories regarding the trigeminovascular complex discussed earlier, as well as with evolving ideas on central sensitization to pain because of repeated noxious stimulation from one body region that may produce a type of centrally mediated allodynia. The role of alternative factors in migraine has been reviewed in the monograph by Lance and Goadsby.
The foregoing observations leave a number of questions unanswered. Is one to conclude that migraine with and without aura are different diseases, involving extracranial arteries in one instance and intracranial ones in another? Is the circulatory change the primary cause of headache, or is it a secondary or coincidental phenomenon? Is diminished neuronal activity (spreading depression) the primary cause of neurologic symptoms (it seems so) and headache (unclear), and is the diminished regional blood flow secondary to reduced metabolic demand? Why are the posterior portions of the brain (visual auras) so often implicated (perhaps because of richer trigeminal innervation of the posterior vessels)? The neural mechanisms that underlie these changes and precisely what is altered by the genetic predisposition to migraine are unresolved. No final reconciliation of all these data is possible and migraine remains incompletely explained.
Migraine with aura should occasion no difficulty in diagnosis if a proper history is obtained. Most often, the symptoms begin as “positive,” that is, scintillation, paresthesia, as opposed to the later “negative” scotoma, numbness, aphasia, or paresis. The difficulties come from a lack of awareness that a progressively unfolding neurologic syndrome may be migrainous in origin and may occur without headache. Furthermore, recurrent migraine headaches take many forms, some of which may prove difficult to distinguish from the other common types of headache, and it should be recognized that migraine headaches need not be severe or disabling. Some of these problems merit elaboration because of their practical importance.
The neurologic part of the migraine syndrome may resemble a transient ischemic attack, focal epilepsy, the clinical effects of a slowly evolving hemorrhage from an arteriovenous malformation, or a thrombotic or embolic stroke. It is the pace of the neurologic symptoms of migraine that distinguish it from epilepsy and most cases of stroke. Furthermore, the positive rather than ablative nature of the symptoms assists in distinguishing it from the usual stroke syndromes.
Recurrent painful ophthalmoplegic cranial neuropathy (formerly ophthalmoplegic migraine, mentioned earlier) may suggest a carotid-cavernous or supraclinoid aneurysm. Transient monocular blindness from carotid stenosis is infrequent in the age group affected most by migraine, but the antiphospholipid syndrome, which has some ill-defined relationship to migraine, does cause episodic unilateral visual loss in this group and should be sought as the explanation for transient monocular blindness with or without headache.