Long term decline of P100 amplitude in migraine with aura

OBJECTIVES To investigate visual function in migraine using visual evoked potentials. METHODS Electroretinograms (ERGs) and visual evoked potentials (VEPs) to single flash (SF) and pattern reversal (PR) stimuli were studied in 92 migraine subjects and 62 controls. RESULTS In subjects with migraine, ERGs to single flash were normal. Mean latencies of the P1 and P2 waves in the SFVEP were increased at the occiput by 6% and 4% respectively, but normal at the vertex. Mean latency of the P100 wave in the PRVEP was increased by 5%. These increases were not related to the presence or absence of an aura or to the duration of migraine. P100 amplitude showed a more complex abnormality. It was increased in migraine without aura by 23% compared with controls, regardless of duration of migraine. In migraine with aura it was similarly increased, by 23%, in cases of short duration, but in addition it showed a sharp decline with duration. In cases with a duration of 30 or more years it was 36% less than in cases of short duration, and 21% less than in controls. CONCLUSIONS Subjects with migraine have constitutionally prolonged VEP latencies and increased P100 amplitude, but the latter declines to below normal in cases with a long history of migraine with aura. This decline may reflect subtle neuronal damage within the visual system from repeated transient ischaemia experienced during the aura. Future electrophysiological and other studies will need to be controlled for duration of migraine history.