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WS8.2 Scalp and Intracranial Ictal EEG
2009 Asian and Oceanian Congress of Clinical Neurophysiology the same absolute measurement error constitutes a smaller percentage of change in latency and distance. Other Techniques of Clinical Value: This workshop will deal with various uncommonly used methods to improve diagnostic yields. These include, in addition to the inching techniques and F wave, stimulation in the palm, recording from the intrinsic hand muscles other than abductor pollicis brevis or abductor digiti minimi in the upper limb and recording from more proximal muscles such as tibialis anterior or gastrocnemius in the lower limb. In essence, the lesion identified on clinical grounds provide the overall orientation for the subsequent physiologic evaluation. Short distances magnify focal conduction abnormalities despite increased measurement error, and long distances, though insensitive to focal lesions, provide better yields and reliability for a diffuse process. Workshop 8. Interpretation of Some EEG Patterns WS8.1 Interpretation of Some EEG Patterns Akio Ikeda * Dept. of Neurology, Kyoto University School of Medicine, Japan E-mail address: [email protected] Clinical EEG has a long history of more than 70 years since 1930s, and it has provided valuable information for clinical diagnosis, classification of seizure disorders and also for additional information for structural abnormality. At the same time, routine interictal EEG is thought to be one of the most abused investigations in clinical medicine (Chadwick, Lancet, 1990). Once the sophisticated neuroimaging techniques such as CT and MRI for morphological analysis have been advanced since 1970s, EEG is regarded as a functional examination with localized information, and thus (1) a strong contribution for morphological abnormality is not expected, and (2) EEG findings should be interpreted rather as specific as possible in order to enhance the value of EEG in the current era. Besides well established knowledge of benign EEG variants and artifacts, digital EEG era has produced added several important problems as follows. In this workshop, interactive session is expected. (1) Well established knowledge of benign EEG variants and artifacts: As the normal variants, spike-like activity, spike-and-wave like patterns, paroxysmal patterns and rhythmic patterns are listed (Wesmoreland, 1983). Spike-like activity (mu activity, wicket spikes, 14&6 Hz positive spikes, small sharp spikes, vertex sharp transients in children, lambda wave, POSTs, breach rhythm) has no aftercoming slow, and it does not interrupt background rhythmicity. Spike-and-wave like patterns (6 Hz spike and wave of WHAM and FOLD), paroxysmal patterns (mittens, drowsy burst) and rhythmic patterns (psychomotor variant, alpha variant, SREDA) are frequently observed and misleading if not properly recognized. Physiological artifacts (eye movements, lateral rectus spikes, photomyogenic responses, photoelectric responses, EKG, ballistocardiograph, EMG, glossokinetic potentials, galvanic skin responses, movement artifacts) and non-physiological artifacts (electrodes, environment noises) may obscure underlying EEG signals and also mislead us. Since EEG records very small electric potentials arising from the cerebral cortices through the scalp, good recording condition is needed to obtain appropriate signal. (2) Problems in the digital EEG era: Artifacts related to aliasing (sampling at a rate that is less than twice the frequency of the high-frequency filter [HFF]) can produce an error of waveform in the actual display of the acquired data, and thus currently EEG machines automatically prevent us from selecting faster HFF based on the sampling rate. Limited resolution of the display system also could produce the similar problems when reviewing EEG waveforms. Projected ground artifact (i.e., if one of either grid 1 or grid 2 input activity in the amplifier falls off or has a poor connection, the remaining one of the two and the ground works as active input; the ground becomes a recording electrodes) is most subtle but important, often misleading artifacts. It occurs rather frequently and is less recognized because actual recording waveforms are not always directly inspected while recording, that would let us lose the chance to find it.
S19 WS8.2 Scalp and Intracranial Ictal EEG Sang Kun Lee * Dept. of Neurology, Seoul National University Hospital, Korea E-mail address: [email protected] Localizable scalp EEGs, during ictal episodes, appear to be rare in neocortical epileptic syndromes. However, studies based on large numbers of patients are also rare. It is important to identify the characteristic patterns of variable neocortical epilepsies and to evaluate their clinical usefulness in the localization of epileptogenic focuses. We retrospectively assessed 394 noninvasive ictal recordings from 86 patients who subsequently underwent invasive study and resective surgery. Ictal EEGs were recorded using a video-EEG monitoring system with electrodes placed according to the International 10 20 system, with additional anterior temporal electrodes. The ictal recordings were analyzed according to localizing accuracy and frequency characteristics. The durations of discrete or regional ictal rhythms were also measured. The percentage of discrete or regional EEGs was 23% in frontal lobe epilepsy (FLE), 52% in lateral temporal lobe epilepsy (latTLE), 70% in occipital lobe epilepsy (OLE) and 10% in parietal lobe epilepsy (PLE). In order of frequency, the localizable ictal rhythms were theta, beta, alpha, delta, and rhythmic spike-and-wave. The duration of discrete or regional ictal rhythms was significantly shorter in FLE and PLE than in other epilepsies. Ictal beta activity was the most common rhythm in discretepatterned EEGs. Structural lesions found by MRI did not significantly affect the localization of epileptogenic focuses in the patients. The type of seizure was not related to the degree of localization, with the exception of simple partial seizure. Intracranial electroencephalographic (EEG) monitoring is an important process in the presurgical evaluation for epilepsy surgery. The key to succeed epilepsy surgery was to identify how much of the presumed “epileptogenic zone” we should remove, guided by subdural electrodes. We analyzed intracranial EEGs in 177 consecutive patients who had undergone resective epileptic surgery between 1995 and 2003. We reviewed various intracranial EEG findings and the extent of resection. We assessed the relationships between the surgical outcomes and intracranial EEG factors: the frequency, morphology distribution of ictal onset discharges, the propagation speed, and the time lag between clinical and intracranial ictal onset. We also investigated whether the extent of resection, including the area showing ictal rhythm and various interictal abnormalities, such as frequent interictal spikes, pathological delta waves, and paroxysmal fast activity, influenced the surgical outcome. Seventy-five (42%) patients were seizure free (Engel class I). A seizurefree outcome was significantly associated with a resection that included the area showing ictal spreading rhythm during the first three seconds or included all the electrodes showing pathological delta waves or frequent interictal spikes. However, subgroup analysis revealed that the extent of resection did not affect the surgical outcome in lateral temporal lobe epilepsy.
S19 WS8.2 Scalp and Intracranial Ictal EEG Sang Kun Lee * Dept. of Neurology, Seoul National University Hospital, Korea E-mail address: [email protected] Localizable scalp EEGs, during ictal episodes, appear to be rare in neocortical epileptic syndromes. However, studies based on large numbers of patients are also rare. It is important to identify the characteristic patterns of variable neocortical epilepsies and to evaluate their clinical usefulness in the localization of epileptogenic focuses. We retrospectively assessed 394 noninvasive ictal recordings from 86 patients who subsequently underwent invasive study and resective surgery. Ictal EEGs were recorded using a video-EEG monitoring system with electrodes placed according to the International 10 20 system, with additional anterior temporal electrodes. The ictal recordings were analyzed according to localizing accuracy and frequency characteristics. The durations of discrete or regional ictal rhythms were also measured. The percentage of discrete or regional EEGs was 23% in frontal lobe epilepsy (FLE), 52% in lateral temporal lobe epilepsy (latTLE), 70% in occipital lobe epilepsy (OLE) and 10% in parietal lobe epilepsy (PLE). In order of frequency, the localizable ictal rhythms were theta, beta, alpha, delta, and rhythmic spike-and-wave. The duration of discrete or regional ictal rhythms was significantly shorter in FLE and PLE than in other epilepsies. Ictal beta activity was the most common rhythm in discretepatterned EEGs. Structural lesions found by MRI did not significantly affect the localization of epileptogenic focuses in the patients. The type of seizure was not related to the degree of localization, with the exception of simple partial seizure. Intracranial electroencephalographic (EEG) monitoring is an important process in the presurgical evaluation for epilepsy surgery. The key to succeed epilepsy surgery was to identify how much of the presumed “epileptogenic zone” we should remove, guided by subdural electrodes. We analyzed intracranial EEGs in 177 consecutive patients who had undergone resective epileptic surgery between 1995 and 2003. We reviewed various intracranial EEG findings and the extent of resection. We assessed the relationships between the surgical outcomes and intracranial EEG factors: the frequency, morphology distribution of ictal onset discharges, the propagation speed, and the time lag between clinical and intracranial ictal onset. We also investigated whether the extent of resection, including the area showing ictal rhythm and various interictal abnormalities, such as frequent interictal spikes, pathological delta waves, and paroxysmal fast activity, influenced the surgical outcome. Seventy-five (42%) patients were seizure free (Engel class I). A seizurefree outcome was significantly associated with a resection that included the area showing ictal spreading rhythm during the first three seconds or included all the electrodes showing pathological delta waves or frequent interictal spikes. However, subgroup analysis revealed that the extent of resection did not affect the surgical outcome in lateral temporal lobe epilepsy.