Lateralization of the P22/N30 precentral cortical component of the median nerve somatosensory evoked potentials is different in patients with a tonicor tremulous form of cervical dystonia

Somatosensory evoked potentials (SEPs) of the median nerve were recorded in 40 patients with the tonic and tremulous form of torticollis and in 40 hea lthy volunteers. Polymyographic recordings of the activity of cervical musc les were performed in all patients with cervical dystonia to determine the dystonic and antagonistic muscles. Patient SEPs were recorded during abnorm al head movement. SEPs in 20 healthy volunteers were recorded with the head in the middle position. SEPs in another 20 healthy volunteers were recorde d with the head rotated 60 degrees to the right. The mean peak-to-peak ampl itude values of the precentral P22/N30 and the postcentral N20/P25 complexe s and their mean side-to-side ratios were calculated in the F3 (F4), C3' (C 4'), and C3+ (C4+) electrode positions in all four groups. In patients with the tonic form of torticollis (group I), an apparent mean P22/N30 amplitud e increase was found above the hemisphere contralateral to the direction of head deviation in both precentral electrode positions, F3(4) and C3(4)'. A statistically significant difference was observed between group I and othe r patient and control groups. In patients with the tremulous form of tortic ollis (group II), an increase in the mean P22/N30 amplitude was found above both hemispheres in both precentral electrode positions F3(4) and C3(4)'; a significant difference was found between group II and both control groups . Lateralization of the P22/N30 component was found only in patients with t he tonic form of torticollis. The mean side-to-side ratio of the precentral P22/N30 component amplitude was significantly different when group I was c ompared with either group II or control groups. No significant difference b etween group II and either control group was found. No significant abnormal ities in the postcentral N20/P25 component were found in either the dystoni c patients or in healthy control subjects. These results might indicate a d ifferent pattern of cortex excitability in patients with tonic versus tremu lous forms of torticollis and therefore may implicate different underlying pathophysiological mechanisms in these two forms of disorder.