State-dependent changes in the N20 component of the median nerve somatosensory evoked potential.

Short-latency components of median nerve somatosensory evoked potentials are generally assumed to be unaffected by sleep and level of arousal. We found that sleep prolongs the latency and alters the morphology of the N20 component in normal subjects. These changes may represent differential effects of sleep on various elements contributing to generation of the N20. Failure to control for patient state may degrade the reliability of clinical somatosensory evoked potential testing.

Dietary erucic acid therapy for X-linked adrenoleukodystrophy.

We investigated the biochemical and clinical efficacy of dietary erucic acid (C22:1) therapy for X-linked adrenoleukodystrophy (ALD). In a double-blind crossover study of patients who were on chronic oleic acid (C18:1) therapy, addition of erucic acid to the diet led to a further reduction in plasma hexacosanoic acid (C26:0) concentration. We treated 12 newly diagnosed ALD patients with a diet enriched with erucic acid and oleic acid for 2 to 19 months. Mean plasma C26:0 concentration decreased to normal by 4 weeks, and the C26:0 composition of plasma sphingomyelin and phosphatidylcholine became normal by 4 months on therapy. Fatty acid analysis of postmortem tissues from 1 boy treated for 10 months suggested that dietary erucic acid entered the heart, liver, adrenal gland, and brain. Eight patients remained on treatment long enough (mean, 12 +/- 3 months) to evaluate their clinical response; 6 of these patients with moderate to advanced disease deteriorated neurologically or showed progression of white matter disease on brain magnetic resonance imaging whereas 2 mildly affected patients remained clinically stable after 10 and 19 months. No adverse effects of the diet occurred. We conclude that dietary erucic acid therapy is effective in lowering plasma C26:0 to normal in ALD patients, and may prevent further demyelination in some mildly affected boys.

Conventional and rapid stimulation evoked potential changes in patients with status epilepticus.

We utilized somatosensory evoked potentials to evaluate 33 patients with status epilepticus who did not have focal neurological etiologies. Eighteen percent of the patients had conventional stimulation evoked potential abnormalities at or above the P14 lemniscal level. Evoked potential abnormalities in this population showed a statistically significant correlation with a poor outcome including patients that died or required dependent care following hospital discharge. Rapid stimulation somatosensory evoked potential testing is a new technology which may be useful to detect more subtle central nervous system injury and was successfully utilized in the acute setting. Combined conventional and rapid stimulation evoked potentials demonstrated that 30% of these patients had abnormal findings. The results demonstrate that a significant percentage of status epilepticus patients have somatosensory evoked potential abnormalities and suggest that conventional and rapid stimulation somatosensory evoked potentials may be useful predictive indicators for predicting outcome and mortality in this condition.

Prognostic value of EEG monitoring after status epilepticus: a prospective adult study.

Despite the significant morbidity and mortality associated with status epilepticus (SE), little is known about changes in cortical function that occur after SE. We evaluated cortical function after clinical SE using continuous EEG monitoring lasting at least 24 h in 180 patients admitted to the Medical College of Virginia Hospitals (MCVH). The major EEG patterns observed after SE were a normal record, burst suppression, after SE ictal discharge (ASIDs), periodic lateralizing epileptiform discharges (PLEDs), attenuation, focal and generalized slowing, and epileptiform discharges. Normalization of the EEG after SE was highly correlated with good outcome. The presence of burst suppression and ASIDs was highly statistically significantly associated with mortality. PLEDs were also highly correlated with mortality, but not to the same degree as burst suppression and ASIDs. In addition, these EEG patterns were still significantly correlated with morbidity and mortality when we controlled for etiology using multivariate logistic statistical analysis. Persistent ictal activity was observed in many patients despite control of clinical seizure activity, indicating the importance of EEG monitoring to determine treatment patterns after clinical seizure activity in SE is controlled. The results indicate that certain EEG patterns (normalization of the EEG, ASIDs, burst suppression and PLEDs) are useful predictors of outcome in SE in addition to etiology. EEG monitoring after control of clinical SE is important to guide treatment of SE and is a useful technique for evaluating prognosis.

Phase synchronized triggering: a method for coherent noise elimination in evoked potential recording.

While standard evoked potential recording techniques reliably attenuate gaussian and white noise, they are not similarly effective in reducing coherent noise such as that induced by power lines. We have presented a technique that will effectively eliminate coherent noise. This technique is especially appealing for clinical settings where 60 Hz artifact and a few discrete frequencies are most troublesome, such as in operating rooms or intensive care units. An added advantage of the technique is that it is especially well suited to applications requiring small sample sizes.

Real-time reconstruction of evoked potentials using a new two-dimensional filter method.

Standard techniques for evoked potential recording extract a stimulus-locked event from accompanying noise by averaging a large number of sequentially obtained responses. This approach is valid only to the extent that the nervous system's electrical response to successive stimuli is identical. The technique is suboptimal for recording unstable evoked potentials which vary with the subject's state and attention. Similarly, standard methods are suboptimal for efficiently analyzing rapid changes such as may be seen in the operating room. We developed an evoked potential recording method that reconstructs the individual evoked responses (or small subaverages of evoked potentials) to a series of stimuli. First, the raw data from an entire series of one to several hundred responses are recorded digitally. Using a frequency domain two-dimensional filter, the data are then filtered twice, once along the data sequence axis for each trial, and again along the cross-trial sequence axis for comparable frequency coefficients in sequential trials. The reconstructed filtered evoked potentials are plotted, with successive responses stacked for easy tracking of component changes.

Repetitive high magnetic field stimulation: the effect upon rat brain.

The effect on rat brain of a large number of stimulations with a high strength pulsed magnetic field was investigated in 31 rats: 10 naive controls, 10 anesthetized controls, and 11 stimulated and anesthetized rats. An investigational magnetic stimulating device with a circular 5.5 inch diameter stimulating head was used. The stimulating coil was energized by 1000 V, 8000A, 200 microseconds half sine pulses at a rate of 8 Hz. The peak field strength was 3.4 T, and the peak field flux was approximately 53,000 T/sec. Stimulation was performed for 20 min at a rate of 8/stimuli per second, for a total of at least 10,000 stimulations. The rats were sacrificed after 8 days, and their brains were examined using light microscopy with hematoxylin and eosin staining, or electron microscopy. Histological samples were taken from the neocortex, the hippocampus, the basal ganglia, and the cerebellum. No significant changes were seen.