A prospective 1 year follow-up study with somatosensory potentials evoked by stimulation of the posterior tibial nerve in patients with supratentorial cerebral infarction

Dynamic changes in upper limb short latency somatosensory-evoked potentials following stroke in the dominant hemisphere

Repeated upper limb short latency somatosensory-evoked potential (USSEP) studies were performed in 19 post-stroke patients and correlated with the clinical evaluation. Examinations were performed on admission to the rehabilitation centre, and again about 10 weeks later. Data analysis focused on the temporal changes occurring in each patient, and the relationship of these changes to the patient's clinical condition. In seven of the 19 patients, no cortical potentials could be detected on admission or follow-up. These patients had the worst clinical outcome. Whenever a cortical potential was found in the first examination, it was also detected in the second. Dynamic changes between examinations were mainly seen in the central conduction time (CCT) and showed an opposite trend in each hemisphere. In the second examination, the average CCT lengthened over the damaged hemisphere ( p < 0.03) but shortened (insignificantly) over the nonaffected hemisphere, relative to the CCT in the first test. A positive correlation ( p < 0.03) was found between the increase in NI/PI amplitude - measured peak-to-peak between the major negative component (NI) of the cortical response and the subsequent positive wave (PI)-and improvement in communication ability, especially comprehension.

The USSEP can serve as an auxiliary tool in monitoring the recovery process of stroke patients. Changes in USSEP components occur over both hemispheres and may serve as markers of brain plasticity.

Somatosensory evoked potentials of the posterior tibial nerve in hemiparetic patients: relation to stance balance and walking ability

OBJECTIVES

To examine the association between stance ability and walking performance of poststroke hemiplegic patients and their posterior tibial nerve somatosensory evoked potentials (SEPs).

DESIGN AND SETTING

Fifteen patients, residents of a geriatric rehabilitation hospital, were evaluated twice, with a 2-week interval between sessions. In each session, clinical tests of stance balance and walking ability were performed, and bilateral SEPs to stimulation of the posterior tibial nerve were recorded. Eight healthy, age-matched control subjects underwent the same tests in a single session, but SEPs were recorded unilaterally. Correlation analysis and analysis of variance (ANOVA) were used for studying the prognostic value of the initial posterior tibial nerve SEP measurements as well as the within- and between-sessions relationships between the clinical-functional tests and the SEP data.

RESULTS

No significant correlations between the initial SEP values and functional improvement were established. Within each session, positive significant correlations existed between decreased latencies of several of the medium-latency SEP waves and the performance of stance and gait tasks. However, the between-sessions improvement in stance balance was not correlated with a decrease in latency of the SEP peaks or with an increase in their amplitudes. As to walking ability, in those patients whose gait significantly improved, a significant shortening of P37 and P54 latencies took place.

CONCLUSIONS

The association between the initial and/or the 2-week changes in SEP of the posterior tibial nerve and improvement in stance and walking abilities is equivocal. In addition, the applicability of SEP measurements is limited by patients' physical status and cooperation. The clinical significance of posterior tibial nerve SEP testing in poststroke hemiparetic patients is therefore debatable.

The prognostic value of cortical magnetic stimulation in acute middle cerebral artery infarction compared to other parameters

The prognostic value of magnetic evoked potentials (MEP), somatosensory evoked potentials (SSEP), age and radiological parameters was determined in 50 patients with acute middle cerebral artery infarction. We performed MEP and SSEP within 4 days and after 6 weeks and 3 months of the infarction and assessed clinical improvement by using the Barthel index (BI) and the Rankin scale. The localization and extent of the infarction was investigated by CT scanning or NMR. All parameters were correlated to clinical outcome and the prognostic significance of each parameter in addition to BI was determined. MEP, SSEP, and age were valuable prognostic parameters in predicting stroke outcome when used together with the BI. However, in stepwise regression analysis using all parameters simultaneously, only MEP and age significantly contributed to clinical outcome in addition to BI. Patients showed a better outcome when their MEP was normal or delayed, measured within 4 days of the infarction, compared to patients with absent MEP. Clinical outcome was better at a younger age.

Inter- and intraindividual variability of posterior tibial nerve somatosensory evoked potentials in comatose patients

Thirty-two sequential posterior tibial nerve somatosensory evoked potentials (PTN-SEP) were recorded in 30 neurologically impaired, ventilated, comatose patients. To establish the time invariance of PTN-SEP in this population, Spearman rank correlations of latencies, interpeak latency, amplitudes, and mean absolute amplitude with time were computed. The results revealed no significant time dependency. The mean, standard deviation, and 5th and 95th percentiles for the inter- and intraindividual distribution of PTN-SEP parameters, pairwise PTN-SEP parameter differences, and direct cross-correlation of PTN-SEP were estimated using bootstrap procedures. The standard deviations of the interindividual distribution of PTN-SEP parameters are two to three times higher than the standard deviations of the intraindividual distributions. The coefficients of variation, that is, standard deviations divided by means, for the intraindividual distribution of latencies ranged from 0.012 to 0.042, of amplitudes from 0.146 to 0.230. The mean maximal cross-correlation coefficient of two randomly chosen PTN-SEP across patients equaled 0.65, and within patients 0.91. These data demonstrate the interindividual variability and intraindividual stability of PTN-SEP. The normal limits of intraindividual variability (1.96 x standard deviation) are 3.76, 1.33, 2.92, 6.00, and 3.04 ms for latencies N1, P1, N2, P2, and interpeak latency P1-N2, respectively. The intraindividual differences of amplitudes N1/P1, P1/N2, N2/P2, and the mean absolute amplitude should not exceed 0.67, 0.67, 0.90, and 0.27 microV or, expressed as quotients, 61, 52, 41, and 61%, respectively. The intraindividual maximal cross-correlation coefficient should not be lower than 0.74 with a lag of < 2.00 ms. The results of this study are of use for discrete and continuous PTN-SEP monitoring on intensive care units and during neuroradiological interventions and neurosurgery.