Transcranial electrical stimulation: significance of fast versus slow charge delivery for intra-operative monitoring.

OBJECTIVES: Motor-evoked potentials (MEP) for intra-operative monitoring due to fast charge (fc: 1.0 Coulomb/s) and slow charge (sc: 0.1Coulomb/s) delivery for multipulse transcranial electrical stimulation (TES) were compared. METHODS: MEPs due to fc (n=162) and sc stimulation (n=182) were performed in parallel in a prospective study. The fc stimulation technique is characterized by an increased steepness of charge delivery with consequent reduction of stimulus duration of 50 micros compared to 500 micros in sc stimulation. Stimulation charges (C=Coulomb) and MEP parameters during spine surgery were analyzed. RESULTS: MEPs were successfully recorded in 15/18 patients under total intravenous anesthesia. The mean charge to induce intra-operative MEPs (stimulation threshold) was significantly less in fc (0.195 mC) as compared to sc stimulation (0.298 mC). With both stimulation techniques, in all patients without impairment of motor function, MEPs could be recorded and no technique was superior with respect to successful stimulation. The mean MEP latencies, amplitudes and the extent of intra-individual variation of MEP parameters during surgery (shift of latency less than 10%, variability of amplitude less than 50%) were not different with both stimulation techniques. CONCLUSIONS: TES with either fc or sc stimulation can be used reliably for intraoperative monitoring. Fc and sc stimulation are comparable with respect to feasibility, intra-individual variability and mean parameters of MEP responses. However, fc stimulation provides a higher stimulation efficiency and requires about 35% less total charge for MEP monitoring.

Testing the dissociative taxon.

A dissociative taxon has been proposed by Waller et al. (1996) to help identify individuals experiencing pathological dissociation. We studied the frequency of taxon membership and tested its validity. A total of 276 students and 204 psychiatric inpatients completed the Dissociative Experiences Scale (DES). In patients with higher DES ratings, the Dissociative Disorders Interview Schedule was administered. Taxon classification applied to 2.9% of non-patients and to 12.7% of patients. No statistically significant relationship was found between taxon membership and the clinical diagnosis of a dissociative disorder. Taxon membership indicates a higher frequency of dissociative experiences but cannot be equated with the presence of a dissociative disorder.

Dissociative experiences and their correlates in young non-patients.

The relationship between dissociation and some of its potential correlates and antecedents was explored. Young medical students (N = 276) completed the Dissociative Experiences Scale (DES), Parental Bonding Instrument (PBI), 20-item Toronto Alexithymia Scale (TAS-20) and Munich Personality Test (MPT). The findings indicate that both personality characteristics (such as alexithymia and neuroticism) and, to a modest degree, environmental factors in terms of the lack of parental care contribute to the dissociation variance.

Relationship of criminality to endogeneity and anxiety in patients with unipolar depression.

The relationship between criminal behavior on the one hand and endogeneity and anxiety on the other hand was investigated in a sample of patients with unipolar depression to help elucidate factors influencing the criminality rate in this population. A lower criminality rate in patients with higher ratings of endogeneity and anxiety was predicted. Clinical records of 179 male and 99 female psychiatric inpatients were retrospectively evaluated using the Newcastle Scale II and Hamilton Anxiety Scale. A full account of conviction records served as a measure of criminal behavior. Forty per cent of male patients and 7% of female patients were criminally registered. A lower criminality rate was indeed found in male and female patients with endogenous type of depression and in male patients with higher anxiety ratings. In a multivariate evaluation, however, sociodemographic variables in terms of age and social class seem to be more important predictors of criminality and all variables we assessed contributed only marginally to the explanation of the criminality variance. Thus, in patients with unipolar depression, sociodemographic factors seem to be of a greater even though still limited importance regarding criminal behavior compared with the clinical variables of endogeneity and anxiety.

SSEP analysis in surgery of idiopathic scoliosis: the influence of spine deformity and surgical approach.

The study was conducted to assess the possible impact of spine deformity in patients with idiopathic scoliosis (IS) on tibial nerve somatosensory evoked potentials (t-SSEPs) and the influence of spine correction upon postoperative SSEP recordings. In 61 consecutive patients undergoing 64 spinal instrumentations, 129 pre- and postoperative SSEPs were analyzed. The degree of spine deformity was assessed by the pre-operative Cobb angle of the major scoliotic curve. In a control group, reference values of t-SSEP latencies were established with respect to body height. In a cohort study, IS patients were compared with healthy controls with respect to t-SSEP latency, amplitude, configuration and interside difference. The results of the analysis showed that preoperative-body-height-corrected t-SSEP latencies were prolonged in 61% of patients, with a pathological interside difference in 23.4% of them. The impairment of t-SSEPs was not related to the extent of spine deformity as assessed by the Cobb angle. Even without occurrence of postoperative neurological deficits, postoperative t-SSEPs showed significantly increased latencies without changes in t-SSEP configuration. The prolongation of t-SSEP latencies was related to the surgical procedure (combined ventro-dorsal approach), but not to the extent of spine correction, level of instrumentation, or number of fused segments. The analysis of preoperative t-SSEPs was of no predictive value for intra- or postoperative neurological complications. t-SSEPs are significantly affected in IS patients, although these patients show no obvious clinical neurological deficits. The extent of t-SSEP impairment is not related to the severity of scoliosis. Even in clinically uneventful surgery, the postoperative t-SSEPs can be deteriorated depending on the surgical approach. This indicates a subclinical impact of spine surgery upon spinal cord function.