Normal visual evoked potentials habituation in chronic daily headache with medication overuse

Objectives: We test here, for the first time, in a group of MOH patients the habituation of the visual evoked potentials, reflecting bioelectrical activity of the visual cortex, an area unrelated to pain matrix. Background: Episodic migraineurs during the interictal phase are characterized by lack of habituation during stereotyped stimulus repetition with different sensory modalities. We recently observed that migraine patients evolved in chronic daily headache due to medication overuse (MOH; ICHD-II 8.2) showed a lack of habituation in somatosensory cortex. Methods: We recorded VEPs (600 sweeps, 15 minute of arc checkerboard, 3.1 reversal rate, 80% contrast) in 11 healthy subjects and in 14 age and gender matched MOH patients. Habituation of the visual EPs was defined as the % change of the N1-P1 amplitude between the 1st and 6th block of 100 averaged responses. Results: No significant differences were observed in single block amplitudes and latencies. Moreover, during the continuous stimulation VEPs habituated normally across the six consecutive blocks in both groups (mean percentage amplitude change -12.8 in HS and - 12.5% in MOH). Conclusions: These results are not in favour of a lack of habituation of the visual cortical responses in medication overuse headache patients. Whether this normal behaviour is due to daily headache inducing ictal EPs normalization, or simply due to the fact that we explored a brain area unrelated to pain processing remains to be determined.