Among those CM patients with CGRP levels below 72 pg/mL, 28% had low VIP levels and just 33.3% responded as compared with 77.4% responders in the remaining 72% who had high VIP levels. Therefore, the probability of being a responder in CM

patients with CGRP levels below the threshold was significantly higher in those patients with high VIP levels vs those with low VIP levels (OR: 6.857; 95% CI: 1.583-29.707; P = .012). Among CM patients with CGRP levels above the threshold, there was only one nonresponder who also had high VIP levels. As already reported by our group using in part subjects included here, this study first confirms that interictal CGRP and VIP levels measured in peripheral blood are increased in a large series of CM learn more patients this website vs healthy subjects with no headache history. In fact, both CGRP and VIP levels in CM were twice those of controls, which should be interpreted as distant signs of activation of the sensory and parasympathetic arms of the TVS, respectively. The levels of these two neuropeptides, and especially of CGRP due to its lower variability, measured in peripheral blood and outside migraine attacks have been proposed as the first biomarkers helpful for a more objective diagnosis of CM in the context of a patient with daily or almost daily headaches and a history of migraine, which could

be of value for a better selection of treatment for CM patients.[9, 10] The impact of CM in terms of quality of life and economic burden is very relevant.13-15 Treatment of CM is not easy.[14] Even selleckchem though in clinical practice we use oral preventatives with efficacy in EM, objective evidence of efficacy in CM is available only for topiramate16-18 and, to a lesser degree, for valproic acid.[19] It was not until

this decade that the efficacy of pericranial injections of 155-195 U of onabotA was shown in two large controlled phase III trials.[11] This efficacy has also been reported in several open studies20-23 and in this series in which three quarters of our patients showed an objective and subjective response to onabotA injections. The exact mechanism of action of pericranial injections of onabotA leading to migraine prevention is still unclear, and reliable potential predictors of response have not yet been identified. In the pooled analysis of the 2 phase III trials with onabotA in CM, there was no positive correlation between 85 possible clinical predictors and response to onabotA.[11] The main finding of the present work is that interictal CGRP, and to a lesser degree, VIP levels are potentially of great help on predicting response to onabotA. In fact, both CGRP and VIP levels were significantly higher in CM patients responding to onabotA as compared with nonresponders.