Variation of electrophysiological parameters with central and peripheral characteristics before and after botulinum toxin injection in patients with chronic migraine

OnabotulintoxinA (BoNT/A) is an effective drug in preventive treatment of chronic migraine (CM). The aim of this study is to search the variation of some quantitative senssory testing (QST) and visual evoked potential (VEP) parameters in CM before and after BoNT/A injection and the relation of this with clinical symptoms. BoNT/A was injected to 22 female patients with CM (mean age 38.1±7.2 years) once according to the protocole of "Phase III evaluation research of prophylactic treatment of migraine". Clinical and electrophysiological evaluations were performed between the intervals of; 1-7 days prior to the injection, 28-35 and 84-91 days after the injection. Control group that was composed of 22 healthy females (mean age 36.6±7.6) were examined once, and any injections were not performed. Characteristics of the headache in CM were recorded in details; visual analogue scale (VAS) and migraine disability assessment (MIDAS) were performed. Allodynia, Beck's Depression and Anxiety Inventory (BDI and BAI), VEP and QST were examined in both groups. During the VEP examination, 6 consecutive blocks, obtained by average of 100 traces, were taken in order to search habituation. Latencies of the N75, P100, N145 waves; amplitudes of the N75-P100, P100-N145 and the average of these two amplitudes (mean amplitude); ratio of amplitudes in 2nd and 6th blocks to the amplitudes in 1st block were evaluated. Hot and cold sensation tresholds from bilateral dorsum of hands; right- and left-forehead were evaluated in QST. The patients had migraine for a mean of 22.5±6.1 years, and CM for a mean of 6.1±3.2 years. They had headache a mean of 22.1±4.0 days per month. 20 of the patients had migraine attacks with visual aura (mean 8.6 times per month) and all of them had migraine attacks with cutaneous allodynia (mean 5.6 times per month) Mean MIDAS score was 3.8±0.4. Mean VAS of the least and the worst pains were 4.6±1.7 and 9.6±0.7 respectively. Patients were using a mean of 18.5±2.9 NSAID and 6.2±2 triptane tablets per month. In patients; BDI ve BAI scores (24.1 and 23.3 respectively) were higher than the control group (9.5 and 3.5 respectively) (p<0.001). The score of allodynia scale in patients (7.8) was higher than the control group (1.3) (p<0.001). No statistically significant difference was observed between the patients with CM and the control group according to the QST. No correlation was found between the presence of allodynia during the last headache and the QST parameters. VEP amplitudes in CM group were higher than the control group; statistically significant difference was found according to left P100-N145 and left mean VEP amplitude values (p=0.039, p=0.022 respectively). When VEPs were classified according to the last headache side, VEP amplitudes were higher in the none headache side. According to VEP habituations, no significant difference was found between the groups. After the BoNT/A injection, the frequency and the severity of the headache decreased (p<0.001); attacks with visual aura and allodynia decreased (p<0.001); BDI (p=0.035), BAI (p=0.013), MIDAS (p<0.001) and score of allodynia scale (p=0.030) decreased. There was no significant difference in the QST parameters. VEP amplitudes increased, amount of habituation did not change. BoNT/A was effective to eliminate headache and related symptoms. Loss of VEP habituation, which was reported in episodic migraine before, was not observed in CM. The increase in the VEP amplitudes after BoNT/A may be related to the decrease in the number of attacks.