Pierre Raoul Noel

Magnetic transcranial stimulation in acute stroke: Early excitation threshold and functional prognosis

Magnetic transcranial stimulation was used in 90 subjects (60 acute ischaemic sylvian strokes and 30 healthy controls) in order to evaluate the clinical value of the excitation threshold (ET) in the estimation of functional prognosis. ET mean values recorded 7, 30 and 90 days after stroke (at D7, D30 and D90) in two distal muscles of the upper limbs of the patients were compared with results obtained in 30 healthy control subjects. The data from the patients who ultimately achieved a satisfactory functional recovery at D90 were compared with those from patients who had not recovered in that time. Our results suggest that ET evolution differs according to functional outcome: (1) ET mean values were increased in the stroke patients at D7, but ET was constantly lower at D30 and D90 in patients who recovered than in those who did not. (2) ET temporal evolution showed a gradual decrease of the mean values from D7 to D90 in both stroke groups. This ET decrease was more marked in the patients who recovered from D30 to D90, but with only minor change after D30. (3) The localisation of the lesion had no significant effect on ET mean values at D7, D30 or D90. We conclude that the predictive value of ET estimation might be utilised at D30 in patients with ischaemic sylvian strokes.

Magnetic transcranial stimulation in non-haemorrhagic sylvian strokes: interest of facilitation for early functional prognosis

Magnetic transcranial stimulation was applied to 40 patients in the early stage of a non-haemorrhagic sylvian stroke. Results were evaluated with regards to the clinical outcomes at days 7, 30 and 90. The presence or absence of an early response had a critical prognostic significance. Response latency and amplitude parameters and the excitation threshold were of little value. Facilitation in patients unresponsive at rest was another determinant parameter since 9 out of 10 such cases ultimately recovered.

Magnetic transcranial stimulation: clinical interest of the silent period in acute and chronic stages of stroke

There is little information on the silent period during facilitation of the target muscle at the acute stage of stroke and the ultimate clinical status. We studied 69 subjects with transcranial magnetic stimulation: 20 matched controls and 49 hemiparetic patients investigated 7 and 90 days after the stroke (D7, D90). We measured the silent period duration (SPD) in the first dorsal interosseous muscle at 10 and 100% of maximal voluntary isometric contraction (VIC). The SPD index (the ratio of SPD at VIC 100% by SPD at VIC 10%) at D7 was matched with the clinical outcome at D90. Two patterns of responses could be determined at D7. In the normal subjects and in 27 out of 32 patients who eventually recovered satisfactory function at D90, the SPDs were stable during facilitation (SPD index 100%). On the contrary, in 10 out of the 17 patients with a poor functional outcome, the mean SPD decreased when VIC was increased (SPD index 80%); besides, their muscle tone was significantly increased at D90. Similar patterns were still present in the patients at D90: the mean SPD indexes were not significantly different from D7. We conclude that in the early stage of stroke, a low SPD index appears to be correlated with the eventual occurrence of spasticity.

Nasopharyngeal recordings of somatosensory evoked potentials document the medullary origin of the N18 far-field☆

Because the nasopharyngeal electrode provides non-invasive access to the ventral brain-stem at the medullo-pontine level we used it for recording somatosensory evoked potentials (SEPs) to median nerve stimulation (non-cephalic reference). After the P9 and P11 far-fields, the nasopharyngeal SEPs disclosed a negative-going component which was interpreted as the near-field equivalent of the P14 scalp far-field generated in the caudal part of the medial lemniscus. Nasopharyngeal SEPs also revealed a large N18 with voltage and features strikingly similar to those of the scalp-recorded N18 far-field. These results suggest that N18 is generated in the medulla and not more rostrally in the brain-stem. The use of a nasopharyngeal electrode as reference for topographic brain mapping is discussed. The paper documents the feasibility and relevance of nasopharyngeal recordings for non-invasive analysis of short-latency SEPs.

Inadequacy of the average reference for the topographic mapping of focal enhancements of brain potentials

The main reason for doing topographic mapping of EEG or evoked potentials is to assess regional changes in brain potentials. The use of an average reference is shown to have perverse effects in this relation, namely because it imposes on the recorded data a zero-centering effect which can reduce, eliminate or even reverse the focal changes of bit-mapped brain potentials. Concurrent studies on a true 3-shell head model suggest that such distortions of human EEG data occur because the average reference is computed from a set of (scalp) recording electrodes which do not survey the bottom half of the head volume so that the integral of scalp-recorded potentials frequently differs from zero. The results also raise the question whether the actual incidence of radial or near-radial (versus tangential) generators has been underestimated in the published data using average reference mapping.

Magnetic transcranial stimulation: dissociation of excitatory and inhibitory mechanisms in acute strokes

Magnetic transcranial stimulation was applied to 12 normal subjects and 30 patients (24 acute and 6 chronic) with hemiparesis contralateral to an ischaemic stroke. In the 24 acute patients, the recordings were made at the 7th day on the contralateral first dorsal interosseous (FDI) muscle. We studied the amplitudes of the motor evoked potential (MEP) responses and the post-MEP silent period durations (SPD) at different levels of stimulation intensity (SI) and voluntary isometric contraction (VIC). The evolution of these parameters was matched to the clinical status of the 24 acute patients evaluated 7, 30 and 90 days after the stroke (D7, D30 and D90). Our results may be summarised as follows: (1) in all cases, the MEP-amplitudes increased with facilitation and SI; (2) in the normal subjects and in patients who did recover, the SPD augmented with stronger SI but was found to be independent on the strength of voluntary contraction; (3) in the acute patients with poor recovery, as well as in the chronic patients with spasticity, the SPD decreased with stronger VIC. It may be concluded that MEP-amplitudes and SPD patterns point out excitatory and inhibitory mechanisms which may be differently affected in cerebral injuries. The association between shortening of the SPD with increasing VIC of the target muscle and poor recovery of the stroke after 3 months could be a useful clinical test to predict eventual recovery early after a stroke.

Origin of N18 and P14 far-fields of median nerve somatosensory evoked potentials studied in patients with a brain-stem lesion

Somatosensory evoked potentials (SEPs) to median nerve stimulation were recorded in 3 patients with a brain-stem or medullary lesion documented by clinical and CT or MRI evidence. The positive P14 and negative N18 scalp far-fields were preserved. The results suggest that P14 reflects the spike volley in caudal medial lemniscus, and that the N18 neural generators are located in the medulla, probably in the dorsal column nuclei and/or the accessory inferior olives.

Bilateral cerebral mediofrontal hypoactivity in Tc-99m HMPAO SPECT imaging.

Fifteen patients who had bilateral mediofrontal hypoactivity and 30 control subjects without this SPECT anomaly underwent Tc-99m HMPAO brain SPECT imaging. Bilateral mediofrontal hypoactivity was found in various neurologic disorders, Including subcortical arteriosclerotic encephalopathy, lacunar state, chronic alcoholism, progressive nonvascular dementia, carbon monoxide poisoning, and diabetes mellltus. This SPECT abnormality was, however, specifically associated with three clinical signs: motor disabilities predominating in the lower limbs, urinary incontinence, and akinetic mutism.

Bilateral primary traumatic oculomotor nerve palsy

Two cases with bilateral traumatic oculomotor palsy are presented. The clinical signs, diagnosis criteria, and mechanisms of injury are discussed with a special emphasis on the absence of early reliable prognosis factors. The possibility of recovery depends on the anatomic lesion and not on the ophthalmologic findings in the acute phase.

Les septicémies a yersinia enterocolitica. À propos d'une observation avec métastase cérébelleuse septique

SummaryThe authors present a new case of Yersinia enterocolitica septicaemia with cerebellar septic metastasis and favourable course under chloramphenicol treatment.They review the 57 reports of such septicaemias published up till now.