Middle-latency somatosensory evoked potentials following median and posterior tibial nerve stimulation in Down's syndrome

Perspectives on pain in Down syndrome

Down syndrome (DS) or trisomy 21 is a genetic condition often accompanied by chronic pain caused by congenital abnormalities and/or conditions, such as osteoarthritis, recurrent infections, and leukemia. Although DS patients are more susceptible to chronic pain as compared to the general population, the pain experience in these individuals may vary, attributed to the heterogenous structural and functional differences in the central nervous system, which might result in abnormal pain sensory information transduction, transmission, modulation, and perception. We tried to elaborate on some key questions and possible explanations in this review. Further clarification of the mechanisms underlying such abnormal conditions induced by the structural and functional differences is needed to help pain management in DS patients.

Somatosensory evoked fields in comatose survivors after severe traumatic brain injury

OBJECTIVE

To evaluate the cortical function quantitatively in patients in the chronic phase of severe traumatic brain injury.

METHODS

Thirteen patients with severe traumatic brain injury due to traffic accident followed by persistent consciousness disturbance and disability were studied. Somatosensory evoked magnetic fields (SEFs) for unilateral median nerve stimulation were measured using a whole-head magnetoencephalography system. The latency and electrical current dipole (ECD) moment for the N20m, P30m, N45m and P60m components were calculated and compared with those of 14 age-matched healthy adults.

RESULTS

The peak latency of N20m was longer (P<0.05) and those of P30m and N45m were shorter (P<0.01) in the patients than in normal adults. The ECD moment of N20m and P30m was smaller and that of N45m and P60m was larger in the patients than in normal adults (P<0.01).

CONCLUSIONS

These results can be explained by the hypothesis that diffuse brain injury induces decreased and delayed input of the somatosensory afferent and compensational amplification of the response in the primary somatosensory cortex. Middle-latency SEFs may be applicable as a cortical functional measure for patients with severe traumatic brain injury.

Middle latency somatosensory evoked potentials: noninvasive source analysis

The sources of the components of short latency somatosensory evoked potential in humans have been identified using electrical source localization, magnetoencephalography, and electrocorticography, but the sources of the middle latency components are less understood. The purpose of this study was to identify the source of the middle latency component N60 of the electrically elicited somatosensory evoked potential (SEP). Noninvasive equivalent electrical multiple dipole source localization technique (BESA) was used. SEPs were recorded from nine healthy subjects with 30 electrodes placed on the scalp. Median nerve at wrist (bipolar electrode), index, and little fingers (ring electrodes) were successively stimulated with 2.1 Hz frequency. A window of 100 ms was analyzed. Spatiotemporal equivalent electrical dipole models, each consisting of four dipoles, explained the three different SEPs, from median, index, and little fingers, with residual variances below 9%. The sources generating N20, P30, and N60 all appeared to locate in the posterior bank of the central sulcus contralateral to the stimulated hand. The location of the dipole number 2, most active around N20 component, differed between the index and little finger models, suggesting that somatotopic organization of the primary somatosensory area of the digits was demonstrated by these models. A radial source (dipole 4) was most active around 60 ms in all three models, thus explaining the N60 component. The location of this dipole did not suggest somatotopic organization specific to the stimulated finger for the 60 ms component.

Age-and height-dependent changes of amplitude and latency of somatosensory evoked potentials in children and young adults with Down's syndrome

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded from 19 scalp electrodes in 34 patients with Down's syndrome (DS) aged 7.4 to 35.7 years and in 16 normal control subjects aged 6.4 to 34.4 years. DS patients showed an increase in amplitude of P22, P45, and N60. P100 latency was significantly shortened. After normalization for height of subjects, N20 and N60 latencies were significantly longer in the patient group than in control subjects. On the other hand, it was possible to observe in both groups a significant trend for MLSEP amplitudes to decrease with age during the age period considered in this work. This study further confirms that the pattern of increase in amplitude of MLSEP components observed in DS is a finding peculiar of this syndrome and is not correlated with early aging processes.

Scalp topographic mapping of middle-latency somatosensory evoked potentials in normal aging and dementia

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded in four groups of subjects: 13 normal young controls (mean age, 17.9 years). 11 normal elderly (mean age, 66.9 years), 11 patients with dementia of Alzheimer's type (DAT: mean age, 70.5), and four with vascular dementia (mean age, 79.3). MLSEPs in normal elderly showed an increase in the latency of P22, N30, P45, N60, and P100, and in the amplitude of N60. DAT patients also presented such changes; however, the increase in the amplitude of N60 was much more evident than that found in normal aging and was accompanied by a significant increase in amplitude of P45. Patients with vascular dementia tended to show longer latencies and larger amplitudes than the other groups. The increase in amplitude of P45 and N60 in MLSEPs seems to be characteristically associated with normal aging and the development of dementia. It is suggested that the mechanism of such functional changes might be correlated with the structural and neurochemical changes accompanying neuronal loss in these conditions.

Neck flexion and extension in children with Down syndrome: a somatosensory study

The cervical spine in Down syndrome patients is often lax, at least at radiographic imaging, and the risk of spinal cord embarrassment is increased. This study was performed to obtain information that would help identify patients at risk for this problem and reduce the risk of endotracheal intubation and other surgical procedures in patients with Down syndrome. Somatosensory evoked potential studies were performed in 15 consecutive children who were undergoing elective otolaryngic surgery. None had neurologic symptoms or the physical examination finding of cervical spinal cord embarrassment, and their cervical spines were considered normal by plain radiographs obtained in the neutral, flexed, and extended positions. No significant change in latency (P = .16) or amplitude (P = .19) was found when the anesthetized children had their necks placed in either full flexion or full extension. With more than 90% certainty, the authors believe that children with Down syndrome who have "normal" plain cervical spine radiographs are exposed to no extra risks from neck flexion or extension during surgery.

Age, sex and mental retardation related changes of brainstem auditory evoked potentials in Down's syndrome

Brainstem auditory evoked potentials (BAEPs) were recorded in 51 Down's syndrome (DS) subjects and compared with those of 38 normal controls; the correlations between the BAEP measures and age, sex, and degree of mental retardation were then evaluated. The DS patients showed a significant reduction in wave V latency and amplitude and in I-III, III-V, and I-V interpeak intervals. An age-related shortening of the I-V interpeak interval found in DS patients was interpreted as being a result of changes in central inhibitory/excitatory mechanisms. In both groups, female subjects presented an I-V interval shorter than that of males but this difference was greater in the DS subjects than in the normal population. The DS patients with severe mental retardation showed significantly longer I-V interpeak intervals than those with moderate retardation; this could be due to the presence of additional central nervous system abnormalities.

Bit-mapped somatosensory evoked potentials in Down's syndrome individuals

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded from 19 scalp electrodes in 19 patients with Down's syndrome (DS), in 13 age-matched normal controls and in 11 aged normal individuals. DS patients showed an increase in amplitude of P22, N30, P45, and N60. P100 latency was significantly shortened. After this potential, DS subjects showed the occurrence of a high voltage negative potential at around 100-110 msec followed by another high-voltage positive deflection; both these components showed a frontal-central distribution and were not observed in the two control groups. MLSEPs of DS subjects show peculiar alterations which could be supported by particular neurometabolic and/or neuropathologic changes.

Pattern-reversal visual evoked potentials in Down's syndrome

We examined pattern-reversal visual evoked potentials (PRVEPs) in 36 adult patients with Down's syndrome, and analyzed the effects of the ophthalmological abnormalities on results of PRVEPs. The P100 latency was significantly delayed in 24 eyes of 16 patients. The P100 latency was significantly longer and its amplitude was significantly smaller (P < 0.001) in Down's syndrome patients than in age-matched normal controls. In 9 patients without any ophthalmological abnormalities, P100 latency showed no significant difference from that in normal controls, but three of them showed a significant delay of P100. Their P100 amplitudes were significantly smaller than those in normal controls. Therefore, we considered that the ophthalmological abnormalities are one of the main factors causing PRVEPs abnormalities in Down's syndrome patients, but some unknown factors should be also responsible.

Scalp topography of somatosensory evoked potentials following median and posterior tibial nerve stimulation in Down's syndrome

The scalp topography of somatosensory evoked potentials (SEPs) following stimulation of the median and posterior tibial nerve of 39 patients with Down's syndrome was compared with that of age-matched normal controls using significance probability mapping (SPM). The maximal area of each potential in Down's syndrome was similar to that in normal controls, but the scalp distribution was wider. The amplitudes of all components, except the N45 and P59 potentials of the posterior tibial nerve SEPs, were greater in Down's syndrome, and the t values calculated by SPM were significantly greater. However, the difference of SEP maps between Down's patients and aged controls (over 65 years) was much smaller than that between Down's patients and age-matched controls. Therefore, we conclude that the generator sources and generating mechanisms of SEPs in Down's syndrome are not different from those of normal control, however SEP potentials in Down's syndrome are remarkably enhanced, resulting in a wider distribution, probably due to accelerated aging in Down's patients.

Late cognitive event-related potentials in adult Down's syndrome

Event-related electroencephalogram (EEG) potentials (ERPs) using two different tasks were measured in 14 adults with Down's syndrome (DS; mean age 32 years) without clinically detectable cognitive decline. Two groups, young healthy (YH) and old healthy (OH) adults, served as controls. In the oddball task, DS had prolonged N1 and earlier P2 latencies than the control groups. P3 latency was delayed in comparison to YH. In the PushWait task, P3 latency was later in DS than in YH and OH. In both tasks, DS showed a marked amplitude shift towards positivity overlapping the N1-P2 complex and seemingly also P3: The P3 amplitude evoked by target tones and by "Push" was shifted towards anterior sites resulting in a Cz maximum. Changes of the N1 latency and amplitude in DS may be related to enhanced arousal during stimulus processing, indicating a possible defect of central inhibitory mechanisms. The study suggests that differentiated ERP procedures provide information on adult DS cognition exceeding those given by mere P3 latency measurements. Such procedures may be useful in the evaluation of the cognitive decline due to precocious aging or Alzheimer-type dementia in DS.

Brain-stem auditory evoked potentials in adults with Down's syndrome

Brain-stem auditory evoked potentials (BAEPs) were examined in 37 adult patients with Down's syndrome and in 37 age-matched normal subjects. All absolute and interpeak latencies except for the interpeak latency IV-V were shorter in patients than in normal subjects. The amplitude of wave V and the amplitude ratio V/I were smaller in patients than in normal subjects. Short latencies in patients were considered to be due to the smaller size of the brain-stem or to faster conduction velocity. The prolonged interpeak latency IV-V and the smaller wave V may indicate physiological dysfunctions between the upper pons and the lower midbrain.