| Objective: To research the characteristic of nystagmus evoked by different conditions in vestibular migraine(VM),and explore the possible mechanism so as to have much better comprehension and identification of VM.Methods: The horizontal nystagmus and vertical nystagmus evoked by caloric test as well as optokinetic nystagmus(OKN)evoked by optokinetic stimulation in 20 patients with VM(VM group)and 18 patients with unilateral moderate to severe Ménière’s disease(MD group)in inter-ictal phase were observed and analyzed.Under positional maneuvers of Dix-Hallpike and Roll-test,the type,latency,duration,slow phase velocity,changed speed of positional nystagmus in 16 patients with VM in ictal phase(VM group)compared with 16 patients with horizontal semicircular canal benign paroxysmal positional vertigo(HC-BPPV group)were analyzed.Results: The total horizontal nystagmus(H-total)and labyrinth reflectivity(LR)in VM group were no significant difference between the two groups(P= 0.396;P= 0.405).There were no statistical difference in abnormal rate of canal paralysis(CP)and direction preponderance(DP)between VM group and MD group(P= 1.000;P= 0.725).The abnormal rate of fixation index(FI)in VM group were significantly higher than MD group(50.00% vs.11.76%;χ2 = 5.931,P= 0.027).The positive rate of vertical nystagmus under caloric evoked test in VM group were more higher than MD group(95.00% vs.66.67%,χ2= 5.061,P = 0.038).In VM group the peak slow phase velocity of vertical nystagmus(V-SPVmax)under caloric evoked test were more higher than MD group(11.86±7.76(°)/s vs.6.71±3.15(°)/s;t’= 2.576,P < 0.05).The total vertical nystagmus(V-total)under caloric evoked test in VM group were significantly higher than MD group(19.47±13.95(°)/s vs.9.12±4.64(°)/s,t’= 2.983,P < 0.05).Significant differences were not found in the difference of vertical nystagmus(V-D)between VM group and MD group(9.81±9.78(°)/s vs.5.17±3.63(°)/s;Z=-1.136,P= 0.256).The score of visual analogue scale(VAS)in VM group were 4.95±2.09,which were statistically lower than MD group(7.22±2.16)(t= 0.102,P= 0.002).There was a linear regression relationship between VAS and V-total in VM group and MD group.The regression coefficients were negative,in VM group r =-0.111,P<0.001;in MD group r =-0.359,P= 0.013;Moreover,there was a linear regression relationship between V-total and H-total in VM group and MD group,in VM group r=0.192,P= 0.008;in MD group r= 0.072,P= 0.001.However,VAS and H-total in VMgroup and MD group were not observed statistically significant linear regression relationship,P values were both > 0.05.The results showed that the abnormal rate of OKN when combined with leftward OKN and rightward OKN were higher in VM group than MD group(35% vs.13.9%;χ2= 4.504,P= 0.038).There were no significant differences in SPV of leftward OKN or rightward OKN between VM group and MD group,P value were both>0.05.The asymmetry ratio of leftward and rightward OKN were not statistically significant(P= 0.907).The mixtures of geotropic,apogeotropic and down beating components with a variable combination of each component and various types of positional nystagmus in an individual with VM were identified.There were no significant difference in lantency,or duration of time of positional nystagmus in horizontal component between VM group and HC-BPPV group(P= 0.290;P= 0.430).The peak slow phase velocities(SPVmax)of positional nystagmus in VM group were(7.30[5.68,19.98](o)/s)which were significantly lower than those in HC-BPPV group(47.95[9.80,114.67](o)/s)(Z=-3.658,P<0.001).The asymmetry ratio of the stronger and softer SPVmax of positional nystagmus in HC-BPPV group were statistically higher than VM group([27.75±15.13]% vs.[49.05±22.86]%;t=-2.703,P= 0.012).The time for reaching to SPVmax(Tm)of positional nystagmus in VM group were quite longer([18.10±6.28]s vs.[6.70±4.13]s;t= 5.544,P<0.001)compared with HC-BPPV group.There were statistically difference in overall ascending speed(OAS)to reach SPVmax of positional nystagmus between VM group and MD group(0.52[0.37,1.18](°)/s2 vs.7.96[2.50,30.62](°)/s2);Z=-3.960,P<0.001).In VM group the ascending speed(AS)of positional nystagmus were(0.34[0.09,0.52](°)/s2),which were significantly lower than MD group(1.55[0.36,3.48](°)/s2)(Z=-2.635,P= 0.008).The descending speed(DS)of positional nystagmus in VM group were 0.50±0.34(°)/s2,which were significantly lower than MD group(3.32±3.24(°)/s2;t’= 3.462,P<0.05).Conclusion: Under caloric condition,horizontal semicircular canal dysfunction can appear in both patients with VM and those of MD,patients with VM are more likely to show abnormal FI than those of MD.The vertical nystagmus evoked by caloric condition are not specific manifestations of VM or MD,while the vertical nystagmus have positive correlation with horizontal nystagmus.The vertical nystagmus evoked by caloric condition may be as the sign of disorder central integration.Patients with VM show more frequent and evident central disorder integration.The abnormal rate of OKN may be helpful to identify VM and MD.Positional nystagmus during Dix-Hallpike and Roll-test in patientswith VM are quite different from those with HC-BPPV.It is supposed that abnormal central integration mechanism in VM may cause discordant transmission the information of semicircular canal rotation,resulting in mixed nystagmus components and flat nystagmus appeared at multiple positional maneuvers. |
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