William W. Sutherling

Presurgical evaluation for partial epilepsy : relative contributions of chronic depth-electrode recordings versus FDG-PET and scalp-sphenoidal ictal EEG

One hundred fifty-three patients with medically refractory partial epilepsy underwent chronic stereotactic depth-electrode EEG (SEEG) evaluations after being studied by positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) and scalp-sphenoidal EEG telemetry. We carried out retrospective standardized reviews of local cerebral metabolism and scalp-sphenoidal ictal onsets to determine when SEEG recordings revealed additional useful information. FDG-PET localization was misleading in only 3 patients with temporal lobe SEEG ictal onsets for whom extratemporal or contralateral hypometabolism could be attributed to obvious nonepileptic structural defects. Two patients with predominantly temporal hypometabolism may have had frontal epileptogenic regions, but ultimate localization remains uncertain. Scalp-sphenoidal ictal onsets were misleading in 5 patients. For 37 patients with congruent focal scalp-sphenoidal ictal onsets and temporal hypo-metabolic zones, SEEG recordings never demonstrated extratemporal or contralateral epileptogenic regions; however, 3 of these patients had nondiagnostic SEEG evaluations. The results of subsequent subdural grid recordings indicated that at least 1 of these patients may have been denied beneficial surgery as a result of an equivocal SEEG evaluation. Weighing risks and benefits, it is concluded that anterior temporal lobectomy is justified without chronic intracranial recording when specific criteria for focal scalp-sphenoidal ictal EEG onsets are met, localized hypometabolism predominantly involves the same temporal lobe, and no other conflicting information has been obtained from additional tests of focal functional deficit, structural imaging, or seizure semiology.

The magnetic and electric fields agree with intracranial localizations of somatosensory cortex

We measured the magnetoencephalogram (MEG), electroencephalogram (EEG), and electrocorticogram (ECoG) after stimulation of contralateral median nerve in four patients with partial epilepsy evaluated for surgery. Quantitative localization estimates from equivalent source modeling were compared with locations of central fissure in hand sensorimotor area determined by cortical stimulations, intraoperative photographs, and examination after excision in frontal lobe. We also measured MEG and EEG in nine control subjects. MEG and EEG localizations were within 2.5 cm of the estimated location of central fissure in all 13 subjects. In the three patients who had complete mapping of all three fields, the average distance of localizations from central fissure was approximately 4 mm in both MEG and EEG, 3 mm in ECoG, and 3 mm in combined MEG and EEG. MEG was simpler than EEG, which was simpler than ECoG. MEG resolved ambiguities in both EEG and ECoG. The combination of the three fields added information about the spatiotemporal activity of somatosensory cortex. Localization of central fissure was essential to surgical treatment.

Comparisons of MEG, EEG, and ECoG source localization in neocortical partial epilepsy in humans

In order to delineate the characteristics of epileptic spikes, 1946 different spikes were studied in 6 patients with complex partial epilepsy. Non-invasive MEG and EEG source analysis of interictal spikes were contrasted to ECoG localization, surgical outcome and presence of lesions on MRI. Results indicated that: (1) using the most frequent occurring spike topography patterns from a large sample of spikes improved goodness-of-fit values for both MEG and EEG localization, (2) when spike patterns could be appropriately matched on several successive MEG measurements to provide an adequate matrix (3 of 6 subjects), there was excellent agreement between MEG dipole sources and ECoG sources as well as surgical outcome and presence of MRI lesions, (3) EEG source analyses also gave good results but not as consistently as MEG.

IFCN recommended standards for short latency somatosensory evoked potentials. Report of an IFCN committee

Short latency somatosensory evoked potentials (SEPs) are the electrical potentials generated mainly by the large fiber sensory pathways in the peripheral and central portions of the nervous system. SEPs can be elicited from almost any large nerve, although the median and posterior tibial nerves are usually chosen. The short latency responses occur within the first 50 msec after a brief stimulus. Other later middle latency and long latency SEPs also occur, but with a wider range of normal variability making clinical use more difficult. The recommended standards set out below address specifically the short latency median and posterior tibial nerve SEPs. Analogous standards should be applied for testing other nerves such as ulnar or peroneal. The literature contains many reports using techniques that differ from those described here. The peaks, latencies, amplitudes and normal limits in those reports will not necessarily correspond to results described here. Age has a significant effect on the SEP. In young children, the N9 and N13 potentials occur quite early, and the central conduction is relatively slow. Among older adults, normal limits for most latencies are longer by 5-10%, most of this change occurring after age 55 years. Similar changes occur for posterior tibial nerve SEPs. The patients limbs should be kept warmed during testing, since cool limb temperatures can slow the peripheral conduction. Peak latencies are significantly correlated with height, whereas interpeak latencies are affected less. Most medications have little effect on these potentials, and so sedation with a benzodiazepine or similar medication may be employed to aid the subject relaxation. Sleep may change the apparent median nerve N20 latency by increasing the amplitude of a peak component slightly later than that used for scoring for testing during wakefulness. This may cause a slight latency asymmetry to appear when one limb is tested with the patient awake and the other with the patient asleep.

Quality of Life of Epilepsy Surgery Patients as Compared with Outpatients with Hypertension, Diabetes, Heart Disease, and/or Depressive Symptoms

Summary: Health‐related quality of life (HRQOL) of 166 adults who had previously undergone surgical treatment for intractable epilepsy was compared with that of outpatients with hypertension, diabetes, heart disease, andlor depressive symptoms. Eight self‐reported HRQOL domains were evaluated and compared by the RAND 36‐Item Health Survey 1.0: emotional well‐being, social function, role limitations due to emotional problems, energy/fatigue, pain, role limitations due to physical problems, physical function, and general health perceptions. A pictorial item on overall QOL was also administered, for a total of 9 HRQOL domains. With adjustment made for age, gender, education, and comorbid conditions, 55 completely seizure‐free patients scored higher (i.e., better health) than patients with hypertension in 6 of 9 domains, higher than diabetic patients in 8 of 9, higher than those with heart disease in all 9, and higher than those with depressive symptoms in all 9 (all p < 0.05). Sixty‐seven patients still having seizures with impaired consciousness scored worse than hypertensive patients in 5 domains, worse than diabetic patients in 3, and worse than heart disease patients in 2; for all 3 conditions, these domains included emotional well‐being and overall QOL (p < 0.05). These 67 patients, however, scored better than patients with depressive symptoms in all 9 domains, better than those with heart disease in 2, and better than those with diabetes in 1 (all p < 0.05). Forty‐four other patients had only simple partial seizures (SPS); their scores were comparable to those of diabetic and heart disease patients on mental and social health scales but were higher (“better”) than those of these patients on physical health scales. HRQOL among patients who have undergone “curative” epilepsy surgery is better than that of patients who have hypertension, diabetes, heart disease, or depressive symptoms. Patients who have continued seizures with altered consciousness are worse off in terms of emotional well‐being and overall QOL than all other patients, except for those with depressive symptoms.

Neuromagnetic investigation of somatotopy of human hand somatosensory cortex

SummaryIn order to investigate functional topography of human hand somatosensory cortex we recorded somatosensory evoked fields (SEFs) on MEG during the first 40 ms after stimulation of median nerve, ulnar nerve, and the 5 digits. We applied dipole modeling to determine the three-dimensional cortial representations of different peripheral receptive fields. Median nerve and ulnar nerve SEFs exhibited the previously described N20 and P30 components with a magnetic field pattern emerging from the head superior and re-entering the head inferior for the N20 component; the magnetic field pattern of the P30 component was of reversed orientation. Reversals of field direction were oriented along the anterior-posterior axis. SEFs during digit stimulation showed analogous N22 and P32 components and similar magnetic field patterns. Reversals of field direction showed a shift from lateral inferior to medial superior for thumb to little finger. Dipole modeling yielded good fits at these peak latencies accounting for an average of 83% of the data variance. The cortical digit representations were arranged in an orderly somatotopic way from lateral inferior to medial superior in the sequence thumb, index finger, middle finger, ring finger, and little finger. Median nerve cortical representation was lateral inferior to that of ulnar nerve. Isofield maps and dipole locations for these components are consistent with neuronal activity in the posterior bank of central fissure corresponding to area 3b. We conclude that SEFs recorded on MEG in conjunction with source localization techniques are useful to investigate functional topography of human hand somatosensory cortex non-invasively.

The magnetic field of epileptic spikes agrees with intracranial localizations in complex partial epilepsy

The magnetoencephalogram (MEG) and electroencephalogram (EEG) were measured during interictal epileptic spikes in nine patients with complex partial seizures. The MEG localization estimates were compared with localizations by intraoperative cortical electrodes, subdural electrodes, stereotaxic depth electrodes, anatomic imaging, postoperative pathologic analysis, and postoperative follow-up. In all patients, MEG localization estimates were in the same lobe as the epileptic focus determined by invasive methods and EEG. In two patients, it was possible to quantify precisely the accuracy of MEG localization by mapping a spike focus that was visually indistinguishable on MEG and cortical recordings. In both patients, MEG localization was approximately 12 mm from the center of the cortical spike focus on intracranial recordings. In eight patients, MEG showed tangential dipolar field patterns on the spontaneous record, but EEG did not. In one patient, a cortical epileptic discharge was detected only on MEG for some discharges and only on EEG for other discharges. The MEG did not detect deep spikes with present levels of environmental noise.

Magnetic localization of a dipolar current source implanted in a sphere and a human cranium

Magnetic fields produced by a dipolar source implanted in a spherical conductor and a human cranial specimen were measured in the magnetoencephalogram (MEG). The location of the source was accurately computed in the spherical conductor from the identified magnetic field extrema using equations for a current dipole in a sphere. This same method was insufficient for localizing the source in a human cranium, where magnetic field maps appeared as distortions from the classical dipolar pattern. A more complete computer modeling procedure was used, adjusting for the non-spherical dimensions of the recording matrix on the cranium. By fitting the gradient of computer simulated fields to those measured outside the cranium, the accuracy of source localization was substantially improved. The greatest distortion of the extracranial magnetic field was an inequality in the measured amplitude of the two extrema, produced by an increased distance and angle of the MEG probe when recording over the lower face and ear. However, gross heterogeneities in the resistance of the skull due to a craniectomy and an implanted insulating balloon had a negligible effect on the extracranial magnetic field pattern.

Interictal cerebral metabolism in partial epilepsies of neocortical origin

We performed interictal [18F]fluorodeoxyglucose positron emission tomography (FDG PET) in 24 patients with partial epilepsy of neocortical origin. Two-thirds of patients had regions of hypometabolism. The zone of intracranially recorded electrographic ictal onset was always located in a region of hypometabolism, in those with hypometabolism. Hypometabolic regions in partial epilepsies of neocortical origin were usually associated with structural imaging abnormalities. Regional hypometabolism occasionally occurred without localizing ictal scalp EEG and cerebral magnetic resonance imaging findings, however. FDG PET may be useful in directing placement of intracranial electrodes for presurgical evaluation of refractory neocortical seizures.

IFCN GUIDELINES FOR TOPOGRAPHIC AND FREQUENCY ANALYSIS OF EEGS AND EPS. REPORT OF AN IFCN COMMITTEE

The past 15 years have witnessed a substantial increase in the use of computer-based data processing for analysis of EEGs and evoked potentials (EPs), driven forward by the microelectronics revolution. Clinical neurophysiology laboratories need to be aware of the procedures and problems encountered in using some of these newly available testing procedures. This report reviews current concepts regarding topographic analysis and frequency analysis of EEGs and EPs. A report of this length can only touch on the major issues involved in the common applications of these techniques, and many other versions of testing are also available (e.g., compressed spectral array) beyond this scope of the current report. The aim of this report is to provide one general guideline for the ordinary use of topographic analysis and frequency analysis. It is not intended to preclude in any way other approaches or techniques. It is understood that research facilities will often use techniques that differ from the simple standards described here.