Pathophysiology of migraine.

The exact pathogenesis of migraine remains to be determined. In particular there is increasing evidence for the neural basis of migraine. We now have a body of data supporting the concept of central neuronal hyperexcitability as a pivotal physiological disturbance predisposing to migraine. The reasons for increased neuronal excitability may be multifactorial. Most recently, abnormality of calcium channels has been introduced as a potential mechanism of interictal neuronal excitability. Mutant voltage gated P/Q type calcium channel genes likely influence presynaptic neurotransmitter release, possibly of excitatory amino-acid systems or inhibitory. It could therefore be hypothesised that genetic abnormalities result in a lowered threshold of response to trigger factors. There is also evidence from spectroscopic studies that magnesium is low in migraine. We currently conceive of a migraine attack as originating in the brain. Triggers of an attack initiate a depolarising neuroelectric and metabolic event likened to the spreading depression of Leao. This event activates the headache and associated features of the attack by mechanisms that remain to be determined, but appear to involve either peripheral trigeminovascular or brain stem pathways, or both. Excitability of cell membranes, perhaps in part genetically determined, is the brain's route of susceptibility to attacks. Factors that increase or decrease neuronal excitability constitute the threshold for triggering attacks.