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Biomedical subjects

J Isnard

Publications and source records attributed to J Isnard.

29 records · Page 2Linked to original sources
PubMed2000

The role of the insular cortex in temporal lobe epilepsy.

The role of the insular cortex in the genesis of temporal lobe epileptic (TLE) seizures has been investigated in 21 patients with drug-refractory TLE using chronic depth stereotactic recordings of the insular cortex activity and video recordings of ictal symptoms during 81 spontaneous electroclinical seizures. All of the recorded seizures were found to invade the insula, most often after a relay in the ipsilateral hippocampus (19/21 patients). However, 2 patients had seizures that originated in the insular cortex itself. Ictal symptoms associated with the insular discharges were similar to those usually attributed to mesial temporal lobe seizures, so that scalp video-electroencephalographic monitoring does not permit making any difference between ictal symptoms of temporo-mesial and insular discharges. A favorable outcome was obtained after a temporal cortectomy sparing the insular cortex in 15 of 17 operated patients. Seizures propagating to the insular cortex were found to be fully controlled by surgery, whereas those originating in the insular cortex persisted after temporal cortectomy. The fact that seizures originating in the insular cortex are not influenced by temporal lobectomy is likely to explain some of the failures of this surgical procedure in TLE.

Adolescent↗
PubMed1999

[Partial non-convulsive status epilepsy in multiple sclerosis].

This report describes the observations of two patients with a several years' history of multiple sclerosis who presented sudden neurologic impairment. The symptomatology was suggestive of a non-convulsive partial status epilepsy. The clinical presentation was a paroxysmal dysphasic phenomenon in the first case without any consciousness impairment, associated with slight right hemiparesis. Electroencephalographic investigations revealed asymmetrical patterns, left-sided slow waves and periodic lateralized epileptiform discharges (PLEDs). Antiepileptic treatments were partially effective and intravenous steroids were needed for complete recovery. For the second patient, clinical presentation was acute psychiatric symptoms with disorientation, alternating manic symptomatology and mutism. Electroencephalography showed left fronto-central rhythmic continuous slow wave and spike wave activity. Intravenous antiepileptic treatment quickly improved the symptomatology. These observations draw attention to the fact that an epileptic cause should not be ruled out when a patient with multiple sclerosis presents sudden neurologic or psychiatric impairment. An early diagnosis allows immediate antiepileptic treatment. Intravenous steroids can be added to stop seizures.

Adult↗
PubMed1999

MRI assessment of the anatomy of optic radiations after temporal lobe epilepsy surgery.

OBJECTIVE: The aim of this study was to determine the course of the temporal optic radiations. MATERIAL AND METHODS: Eighteen patients were included in this prospective study. All of them underwent a temporal lobectomy for epilepsy, including the mesial temporal structures and a variable extent of lateral neocortex (from 2 to 7 cm behind the temporal tip). An MRI was performed 2 months postoperatively, allowing assessment of the extent of lateral resection. Postoperative visual fields were determined by automatic static perimetry (ASP). RESULTS: (1) No patient complained of a disabling visual field deficit. (2) ASP, a highly sensitive technique, however, detected postoperative visual field deficits in 83% of patients, confined to the superior homonymous field contralateral to the resection. (3) A strong correlation was found between the presence of a visual field deficit and the extent of laterotemporal resection. (4) The smallest anteroposterior resection resulting in a field defect was limited to 20 mm from the temporal tip. CONCLUSION: (1) This study confirms a strong correlation between postoperative visual field deficits and the extent of lateral neocortical temporal resection. (2) The anterior limit of Meyer's loop is likely to be located more rostrally than previously believed. (3) Despite this, lateral resection remains useful in some cases for seizure control.

Adult↗
PubMed1998

Topographical reliability of mesio-temporal sources of interictal spikes in temporal lobe epilepsy.

PURPOSE: Localization of hippocampal paroxysmal activities in temporal lobe epilepsy (TLE) by means of dipole modeling has often been criticized because of the supposed inaccuracy of this technique in localizing deep sources of EEG signals. This study aimed at assessing the relevance of mesio-temporal dipoles, as identified by modeling of scalp recorded spikes in TLE. METHODS: Surface and depth EEG activities were simultaneously recorded using scalp and intracranial electrodes implanted through the foramen ovale (FO) in 3 patients with refractory TLE seizures. Intracranial FO spikes were used as triggers for scalp EEG averaging. The averaged signals were modeled by current dipoles, the localization of which were fused with patients' 3D-MRI. RESULTS: Individual FO spikes were undetectable on visual analysis of raw scalp EEG but were reflected by low-amplitude scalp EEG transients on averaged signal. Dipole modeling of this EEG deflection consistently identified a mesio-limbic source in a position close to that of the FO pole recording the intracranial spike with its maximal amplitude. CONCLUSION: This result suggests that mesio-temporal sources can be accurately localized by modeling the signals recorded on the scalp, thus validating the anatomical and clinical relevance of hippocampal sources identified by modeling scalp interictal averaged spikes in TLE.

Adult↗
PubMed1998

A stereoelectroencephalographic (SEEG) study of light-induced mesiotemporal epileptic seizures.

PURPOSE: This study explored the mechanism of light-induced complex partial seizures by using ictal intracerebral recordings in a patient with refractory epilepsy of the right temporal lobe. METHODS: Presurgical evaluation of this patient was realized by means of video-EEG recordings, WADA test, magnetic resonance imaging (MRI), F18-deoxyglucose and C11-flumazenil positron emission tomography (PET) interictal neuroimaging data, and stereoelectroencephalographic (SEEG) ictal recordings. RESULTS: SEEG investigations demonstrated the right mesiotemporal origin of all the patient's seizures. This result was confirmed by a successful right temporal lobectomy. Moreover, SEEG recordings revealed a frequent interictal spiking activity in the right occipital visual cortex that was undetectable on scalp recordings. However, the occipital cortex was not involved at the onset of mesiotemporal ictal discharges and was not hyperresponsive to focal electrical stimulation. CONCLUSIONS: This study shows that, in spite of interictal occipital spiking, the photosensitivity of mesiotemporal seizures can be observed in both the absence of occipital cortex involvement during ictal discharges and demonstrable hyperexcitability of the occipital cortex to light or direct electrical stimulation.

Adult↗
PubMed1994

[Clinical and electroencephalographic manifestations during the Wada test using intracarotid injection of methohexital (Brietal)].

In this retrospective study we report our 12 years' experience of the Wada test (intra-carotid injection of short half-life barbiturates) using Methohexital. The clinical manifestations induced by Methohexital were similar to those observed with Amobarbital. The inocuity of the test is attested by the finding that no incident or accident has been reported in 126 injections, the risk being the same as for arteriography. The two main advantages of Methohexital over Amobarbital are: 1) short hemispheric narcosis, which makes it possible to explore the two carotid arteries territories during the same session and limits the risk of drug diffusion to the two hemispheres; 2) the rare occurrence of vigilance troubles such as drowsiness or falling-asleep, which are frequently observed during Amytal Wada test. Intracarotid Methohexital injections are effective to determine the hemispheric lateralization of language and useful to evaluate the role of each hemisphere in memory, especially before the surgical treatment of drug-resistant focal epilepsies.

Brain Diseases↗
PubMed1993

[Indentation sign in the sylvian sulcus and the arterial origin of an acute subdural hematoma. Contribution of computerized tomography].

Thirty-two traumatic subdural haematomas were operated between 1984 and 1990. In 16 cases (50%), we encountered, after removal of the heamorrhage, a bleeding from a cortical artery at the lateral sulcus (middle cerebral artery). Four mechanisms of arterial bleeding have been reported: a) rupture of a cortico-dural bridging artery, b) "fire-hose" rupture, c) rupture at the level of an arachnoid attachment and d) rupture at the level of a dural adhesion. The characteristic finding of such haematomas on computerized tomography (CT-scan) was an indentation towards the lateral sulcus. This was called the "double brackets sign". In seventy-nine percent of subdural haematomas of arterial origin, the "double brackets sign" was demonstrated on CT-scan on at least two slices (9 mm). In 9% of subdural haematomas of non-arterial origin, this sign was absent or present in only one CT image. The characteristic "double brackets sign", when present on 3 or 4 CT-scan images, seems to have a very high specificity for an arterial origin of the haematoma.

Acute Disease↗
PubMedDate not supplied

Apomorphine-induced relief of the akinetic-rigid syndrome and early median nerve somatosensory evoked potentials (SEPs) in Parkinson's disease.

Among early cortical median nerve SEPs the frontal N30 potential is known to show amplitude reduction during execution of voluntary movements and to be abnormally reduced in parkinsonian patients. However, it is not clear whether N30 abnormalities are related to the severity of motor disability in Parkinson's disease. To address this question we studied median nerve SEPs, using a 16-channel montage, in 7 patients chronically treated with subcutaneous (s.c.) injections of apomorphine hydrochloride for spontaneous "on-off" motor fluctuations. We observed no significant changes in the latency, amplitude or scalp topography of early SEPs when comparing traces and maps obtained in the "off" condition and during the "on" phase induced by s.c. injection of apomorphine. The absence of any SEP changes, despite a clear-cut relief of the akinetic-rigid syndrome, suggests that early cortical SEPs, and in particular the frontal N30 potential, at least when recorded in a subject at rest, are not usable as an objective means to assess the severity or the fluctuations of motor disability in Parkinson's disease.

Aged↗
PubMedDate not supplied

[Tactile agnosia and dysfunction of the primary somatosensory area. Data of the study by somatosensory evoked potentials in patients with deficits of tactile object recognition].

The question as to whether a failure of recognition unrelated to impaired sensory processing or to disorder of naming can occur in the somato-sensory modality has been eagerly debated in the french neurology. Taking as an argument the fact that he had never observed a tactile agnosia in the absence of subtle sensory deficits Dejerine denied the localizing value of tactile agnosia (or asterognosis). Conversely Delay, 20 years later, identified tactile performances such as discrimination of texture and shapes, which he considered as a specific neocortical function, that were lost in parietal syndromes with astereognosis and preserved elementary sensations. He also coined the term "tactile asymbolia" to qualify the patients with astereognosis in whom these performances are preserved. When referring to the definition of agnosias only "tactile asymbolia" should be considered as a "true" tactile agnosia. The recording of early somatosensory evoked potentials (SEPs) now offers the possibility of assessing non invasively the function of the primary somatosensory cortex (in particular area 3b). We have recorded SEPs to median nerve or finger stimulation in 309 subjects with a focal hemispheric lesion presenting with a somatosensory deficit of any type. We could confirm that asterognosis referable to impaired discrimination of textures and/or shapes in the absence of impaired elementary sensation is quite rare since it was observed in only 12 of our patients (3.9%). Moreover early cortical SEPs reflecting the activity of the primary somatosensory area (N20 or/and P27) were clearly abnormal in all of them. A single patient of this group of 12 could be considered as a case of tactile asymbolia but his early cortical SEPs were abnormal. The only condition combining a failure of tactile recognition of objects with normal early SEPs is represented by the "tactile anomia" observed in callosal dysconnexions. Thus, in our patients unable to identify objects by palpation in spite of preserved elementary sensation, we were unable to identify a case of pure tactile agnosia. These results are to be confronted with the recent observation by Caselli (1991, 1993) that tactile object recognition is partially, but selectively, impaired in inferior parietal lesions supposed to disconnect the ventrolateral associative somatosensory cortex from its limbic targets.

Adult↗