Contingent negative variation: methods and potential interest in headache.

Contingent negative variation (CNV) is an event-related slow cerebral potential which has been found abnormal in migraine. Its methodology is described. Contrary to other neurophysiological techniques, CNV needs special equipment and expertise. On average, CNV amplitude is increased and its habituation is lacking in migraine without aura between attacks, but not in migraine with aura. The sensitivity of CNV as a diagnostic tool is low, but its specificity is high. CNV amplitude normalizes after treatment with beta-blockers. The CNV abnormalities in migraine might be due to hyperreactivity of central catecholaminergic pathways

Contingent negative variation and efficacy of beta-blocking agents in migraine

Thirty-three patients with common migraine underwent contingent negative variation (CNV) recordings before receiving prophylactic beta-blocker treatment with either metoprolol (27 patients) or propranolol (6 patients) at mean daily dosages of 110 mg and 122 mg, respectively. After 3 months the therapeutic efficacy of the beta-blocker was assessed in each patient by means of a global severity score and compared with the initial CNV recordings. The mean clinical improvement was 62%. A significant positive correlation was found between CNV amplitude before prophylaxis and the clinical response to beta-blockers: patients with higher CNV tended to respond better to therapy. Eight of 10 patients with a CNV amplitude higher than -25 microV had a more than 50% reduction of the severity score--that is, a good or excellent response to the beta-blocking agent--whereas only 2 of 9 patients with an amplitude lower than -20 microV had a good response