Headache frontiers: using magnetoencephalography to investigate pathophysiology of chronic migraine.

Episodic migraine (EM) may evolve into disabling chronic migraine (CM). The progression is elusive but may be underpinned by central excitability change. Recently, several studies have investigated visual cortex excitability in different migraine disorders using magnetoencephalography, a technique superior to traditional scalp electroencephalography in measuring cortical excitability. These studies replicated the earlier visual evoked potential findings that the visual excitability in EM is dynamically modulated, featured by an interictal lack and ictal recovery of the habituation (ie, response attenuation to repetitive stimulations) in visual evoked responses. Moreover, the excitability in CM presented with a persistent ictal-like dysfunction in interictal recordings, which shifted in tandem to the pattern characteristic of EM after a clinical remission from CM to EM. A sustained potentiation (response augmentation) further differentiates CM with the rare phenotype of persistent visual aura from EM or CM alone. To conclude, visual cortex excitability is a potential biomarker of migraine disorders and its neuroplasticity is associated with CM evolution or remission.