|
 |
|
|||||||
|
|||||||||
Correspondence: When an article is eligible for submission of Correspondence, a link to the response form is available within the full-text article. You must be a current subscriber who has activated the online portion of your subscription in order to send a Correspondence. Any reader can read published Correspondence.
Correspondence to:
|
|
Correspondence:Correspondence published:
-
![[Read Correspondence]](/icons/misc/sectionDOWN.gif)
Reply to Luders et al
- Ekaterina Pataraia (22 June 2004)
-
Does magnetoencephalography add to scalp video-EEG as a diagnostic tool in epilepsy surgery?
- Hans O. Luders, Masaki Iwasaki (22 June 2004)
|
|
|||
|
Ekaterina Pataraia, University of Texas, Department of Neurosurgery 1333 Moursund Ste H 114, Housotn, TX, 77030
Send Correspondence to journal:
ekaterina.pataraia{at}akh-wien.ac.at Ekaterina Pataraia
|
Drs. Lüders and Iwasaki raise a number of important issues regarding the optimal approach for evaluating the clinical efficacy of presurgical MEG studies. They point out that the scope of these studies is to identify the irritative zone which typically includes the ictal zone. In contrast, the basis of non-invasive video-EEG (vEEG) studies is ictal activity emanating from the primary focus, yet by definition, the spatial resolution of the technique is limited. From these facts, we attempted to compare the two fundamentally different non-invasive methods for determining the epileptogenic zone. Given that MEG is a new and relatively expensive method that is not used in all preoperative evaluation centers, large- scale studies are needed in order to demonstrate the relative merit of this method among other widely available techniques (non-invasive vEEG in this case). In parallel with other recent studies [6], and the submitted article cited by Drs Lüders and Iwasaki, our goal was to identify which subset of patients may benefit the most from MEG, rather than advocating the indispensability of MEG. To achieve this goal, we evaluated the predictions of interictal MEG and ictal surface vEEG separately, against the resected zone which was determined by integrating information from all standard presurgical evaluation methods commonly available at tertiary epilepsy centers. Future studies with larger samples are needed to assess the additive advantage of MEG localization data on surgical outcome. The moderate sample size of 82 operated patients reported by us was sufficient to reveal statistically significant results, and to draw the conservative conclusion that a substantial proportion of patients (40%) with either non-localizable or partially localizable vEEG results may benefit from an interictal MEG study. This information alone, provided that it is confirmed by later studies, will provide clinically significant input to the selection of candidates for expensive non-invasive tests, including MEG. References 6. Stefan H, Hummel C, Scheler G, et al. Magnetic brain source imaging of focal epileptic activity: a synopsis of 455 cases. Brain 2003;126:2396- 2405. |
|||
|
|
|||
|
Hans O. Luders, Cleveland Clinic Foundation 9500 Euclid Avenue, Cleveland, OH 44195, Masaki Iwasaki
Send Correspondence to journal:
scolarc{at}ccf.org Hans O. Luders, et al.
|
We read with interest the article by Pataraia et al. [1] who conclude that all patients in whom non-invasive video-EEG studies are either only partially localizing or non-localizing should have MEG. We feel this is a carefully done study but that the results do not justify the conclusions. Interictal MEG, the same as interictal EEG, is a technique used to define the irritative zone. The seizure onset zone usually is only a small subset of the irritative zone. [2] It is difficult to understand why Pataraia et al lumped the irritative zone and ictal onset zone together and then compared them with the MEG defined irritative zone. A much more meaningful comparison would be to compare the irritative zone defined by EEG and by MEG. [3,4] Dr Pataraia et al compared the visual analysis of EEG with the dipole source localization of MEG. Dipole modeling always gives a point-like answer in the head space, no matter how extensive the area of cortex that generates epileptic spikes. In contrast, visual analysis of EEG estimates an area (frequently a large part of a lobe) from which the spikes are generated. Therefore we would expect that the dipole analysis has a better chance of “perfect” overlap with the surgically resected area compared to the EEG. Unfortunately, this factor was not considered by Dr Pataraia et al. Dr Pataraia et al assumed that MEG was correct when it accurately predicted the area of resection regardless of seizure outcome after surgery. The study would be much more convincing if the authors only included patients who were seizure free after surgery. In real life presurgical evaluation, the results of all the tests are analyzed together to increases the ability to localize the epileptogenic zone. To assess the value of the MEG without considering the other results, especially MRI, is certainly of very limited value. To answer the question if MEG is an indispensable test, we should compare “video-EEG + other evaluations” versus “video-EEG + other evaluations + MEG”, and define whether the addition of MEG indeed leads to a better surgical outcome. [5] References 1. Pataraia E, Simos PG, Castillo EM et al.Does magnetoencephalography add to scalp video-EEG as a diagnostic tool in epilepsy surgery? Neurology 2004; 62: 943-948. 2. Rosenow F, Lüders H. Presurgical evaluation of epilepsy. Brain 2001;124:1683-1700. 3. Foldvary N: Ictal electroencephalography in neocortical epilepsy. In: Lüders HO, Comair YG, eds. Epilepsy Surgery. Philadelphia: Lippincott Williams and Wilkins, 2001:431-439. 4. Iwasaki M, Pestana E, Burgess, R.C, et al. Detection of Epileptiform Activity by Human Interpreters: Blinded Comparison Between Electroencephalography and Magnetoencephalography. (submitted) 5. Lesser RP. MEG: good enough. Clin Neurophysiol 2004;115:995-997. |
|||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |