Biomedical subjects

Hermann Stefan

Publications and source records attributed to Hermann Stefan.

23 records · Page 2Linked to original sources

PubMed2002

Post-apoplectic reorganization of cortical areas processing passive movement and tactile stimulation--a neuromagnetic case study.

Magnetoencephalography (MEG) was used in a patient with right centro-parietal stroke to investigate the cortical processing of tactile pneumatic stimulation and passive movement of the impaired left and unaffected right-hand index finger. Source localization of somatosensory evoked magnetic fields (SEF) recorded 2 weeks after infarction demonstrated a spatial displacement of the contralateral SI generators in the affected hemisphere. The distance between SI sources activated by either stimulation technique was noticeably enlarged in comparison to the left hemisphere and to previous data from 12 healthy subjects. Follow-up MEG after 6 months revealed a closer spatial arrangement of the two modality-specific SEF generators and a diminution of the interhemispheric asymmetry of proprioception-related SI sources. The topographical alterations were accompanied by clear clinical improvement of both joint position sense and tactile sensation. The occurrence of ipsilateral SI activity following passive movement of only the impaired index finger might suggest a disinhibition of subthreshold, transcallosal excitatory pathways.

Brain Ischemia↗

PubMed2002

Somatotopic organization of the ventral and dorsal finger surface representations in human primary sensory cortex evaluated by magnetoencephalography.

Cortical reorganization of the subtly differentiated hand map after peripheral nerve injury might be better understood if there was a topographic conception of the homuncular representation of the dorsal finger surfaces in humans, in addition to the well-established sequential rostrocaudal array of the ventral finger aspects in cortical area 3b. In the present magnetoencephalographic study, tactile pneumatic stimulation was delivered to the fingertip and to the ventral and dorsal proximal phalanx of each digit of the dominant hand in 20 right-handed volunteers. Source localization of equivalent current dipoles underlying the recorded somatosensory evoked magnetic field was performed using a Cartesian coordinate system established by the anatomical landmarks nasion and preauricular points. Of the first major peak of each somatosensory evoked field, the region with the maximum field power (root-mean-square across channels) was selected for source reconstruction. Analysis of variance for repeated measures yielded significant results with respect to the arrangement of digits along the vertical coordinate axis, demonstrating a sequential array from the most inferiorly located D1 to the most superiorly located D5 for all different stimulus positions. This is the first study providing evidence for a sequential topographical arrangement of not only the ventral but also the dorsal surface representations of the individual digits in the human somatosensory cortex. The study contributes to a better understanding of the somatosensory hand representation in human primary cortex and provides useful information with regard to cortical plasticity studies in patients with peripheral nerve injuries at the upper extremity.

Adult↗

PubMed2002

Clinical effects of topiramate against secondarily generalized tonic--clonic seizures.

OBJECTIVE: Intensive and quantitative evaluation of the duration, intensity and frequency of tonic and clonic signs of secondarily generalized tonic-clonic seizures (GTCS) in patients with pharmacoresistant partial seizures during topiramate (TPM) treatment. METHODS: Thirty patients suffering from refractory partial seizures with secondarily GTCS undergoing presurgical evaluation were randomized into a low dosage (100 mg daily) and a parallel medium dosage (200 mg daily) group of TPM add-on medication (15 patients for each group). Study phases included a 3 days baseline video-EEG phase, a 10 days TPM titration phase without video-EEG and a 3 days TPM dose maintenance phase with video-EEG. During the baseline and the dose maintenance phase seizures were recorded using video-EEG monitoring and the following parameters were measured for each recorded secondarily generalized tonic and clonic signs: duration (lasting seconds), intensity (on a 0-3 scale), frequency (numbers per 24 h). RESULTS: A total of 46 complex partial seizures with secondarily generalized tonic-clonic signs during the baseline phase and 20 during the dose maintenance phase were intensively analyzed. More patients in the medium dosage group than in the low dosage groups were free from secondarily GTCS during the dose maintenance phase (nine vs. two, P<0.05). Intergroup comparison suggested that the duration of all tonic signs decreased more in the medium dosage group computing the reduction from baseline to the dose maintenance phase (P<0.05). There were statistically more significant reductions in the duration and intensity of clonic signs in the medium dosage group (P<0.05). CONCLUSION: TPM has an early dose-dependant effect on secondarily GTCS in patients with pharmacoresistant partial seizures. SHORT COMMUNICATION: The present study intensively analyzed the duration, intensity, and frequency of secondarily generalized tonic and clonic signs in patients with pharmacoresistant partial seizures. The quantitative data suggested that TPM had a robust early inhibitory effect on secondarily generalized tonic-clonic signs; effects were more prominent in the medium dosage group (200 mg daily) than in the low dosage group (100 mg daily).

Adolescent↗

PubMed2002

Influence on ictal seizure semiology of rapid withdrawal of carbamazepine and valproate in monotherapy.

PURPOSE: To quantify changes in ictal seizure semiology during rapid withdrawal of carbamazepine (CBZ) and valproate (VPA) from a monoregimen in presurgical evaluation. METHODS: Therapeutic intensive seizure analysis (TISA) with video-EEG monitoring was used in 33 patients with pharmacoresistant partial epilepsy undergoing complete withdrawal of CBZ (20 patients) or VPA (13 patients) from a monoregimen. Monitoring phases included a 3-day baseline phase, a 3-day rapid antiepileptic drug (AED) withdrawal phase, and another 3-day AED-free phase with AEDs in subtherapeutic levels. Seizure variables as complete processes and their various elements (ictal signs) were analyzed, including duration (seconds), intensity (on a scale of 0 to 3), frequency (number per 3 days), and total duration of seizures and ictal signs in 3 days (seconds). The localization of seizure patterns on ictal EEG recording (EEG seizure onset) and the first appearing clinical ictal phenomena (initial ictal signs) were recorded. RESULTS: A total of 188 seizures in the CBZ group and 57 seizures in the VPA group were investigated. Compared with the baseline phase, the CBZ group showed increases in duration, frequency of seizures, various ictal signs, and secondarily generalized tonic and clonic signs during the following two phases. Significantly increased values of the VPA group were observed in seizure duration and frequency of hypermotoric phenomena during the AED-free phase. More patients in the CBZ group had secondarily generalized clonic signs during the AED-free phase. EEG seizure onset and initial ictal signs showed no obvious changes between study phases. CONCLUSIONS: Withdrawal of CBZ is followed more quickly by an increase of seizure frequency and severity than is the case for VPA withdrawal. Both CBZ and VPA withdrawal influences seizure propagation rather than the seizure-onset characteristics, which speaks in favor of its use in presurgical evaluation.

Adult↗

PubMed2002

Use of intraoperative magnetic resonance imaging in tailored temporal lobe surgeries for epilepsy.

PURPOSE: We investigated whether intraoperative magnetic resonance imaging (MRI) was able to assess immediately the extent of a tailored temporal lobe resection for epilepsy in comparison to delayed postoperative MRI. The recently proposed concept of an individually tailored procedure, preserving tissue not involved in seizures, leads to a variety of differently shaped resections. METHODS: For intraoperative imaging we used a Magnetom Open 0.2 Tesla scanner. Fifty-eight patients undergoing temporal lobe resections for pharmacoresistant epilepsy were investigated. Half of these were nonlesional. All patients had delayed postoperative follow-up scans, which were compared with the intraoperative, postresection images. RESULTS: In 49 (84%) of 58 cases, intraoperative MRI depicted the resection cavity identical to delayed postoperative studies. Complete resection of the visible lesion was primarily proved in 23 of the 29 cases. In two patients with lesions and in one nonlesional case, the resection was extended after intraoperative imaging, thus increasing the rate of total resections in gliomas from 73 to 87%. In four patients, an extension into eloquent areas did not allow complete removal. In the nonlesional cases (n = 29), the extent of tailored temporal resections also could be exactly documented intraoperatively. CONCLUSIONS: Intraoperative MRI allowed a reliable evaluation of the localization and extent of resection in epilepsy surgery within the operative procedure. Furthermore, it provided the possibility of an image-based correction of an initially incomplete resection, particularly in lesional cases. In the majority of patients, the intraoperative images would have been able to replace delayed postoperative MRI. However, in 16%, there were postoperative changes in the resection volume.

Adolescent↗