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Modern electroencephalography: its role in epilepsy management
Clinical Neurophysiology 111 (2000) 1137±1138
www.elsevier.com/locate/clinph
Letters to the Editor Modern electroencephalography: its role in epilepsy management I was left rather confused by one of the main conclusions put forth by Drs. Binnie and Stefan in their otherwise excellent and comprehensive review of modern EEG in epilepsy (Binnie and Stefan, 1999). It is concluded that routine EEG examination `is of little value' for diagnostic screening because `the sensitivity of the waking interictal EEG for detecting epilepsy and its speci®city for distinguishing epilepsy from other episodic disorders are both very limited.' Nevertheless, in the section on diagnostic sensitivity the review of the relevant literature (including Dr. Binnie's own data) indicates a sensitivity of 92% for the demonstration of interictal epileptiform activity in epileptic patients with serial recordings. The next section goes on to describe a diagnostic speci®city ranging from 97% (in unselected subjects with and without cerebral dysfunction) to greater than 99.5% (in adults without known cerebral dysfunction). I understand, and agree with, a desire to discourage thoughtless `rule out epilepsy' referrals, and this desire is implicit in the authors' statement that the EEG is `of most utility when directed to the solution of appropriate and clearly de®ned problems.' However, an accurate diagnosis and classi®cation of epilepsy cannot be arrived at in all (or perhaps even most) patients on clinical grounds for a variety of reasons well described in the review. It seems to me that the diagnostic question most often faced by the clinician is simply: `Does this particular patient have epilepsy, and, if so, what type?' This is a clear problem for which diagnostic EEG screening would appear to be ideally suited to provide a solution. References Binnie CD, Stefan H. Modern electroencephalography: its role in epilepsy management. Clin Neurophysiol 1999;110:1671±1697.
Richard Wennberg
PII: S 1388-245 7(00)00287-X
Toronto Western Hospital, University of Toronto, Toronto, ON M5T 2S8, Canada
Reply to R. Wennberg There does not appear to be any fundamental difference of philosophy between Dr. Wennberg and ourselves, but a distinction does need to be made between the ideal of problem orientated investigation, which includes establishing the presence and type of epilepsy when these are in doubt, and `routine screening' by EEG. The reality of EEG practice in many European departments is close to that described by Hopkins and Scambler (1977), who commented: `¼it is remarkable that short paper records have been carried out for nearly 40 years with so little bene®t to patients or doctors. A biochemical test with so many false negatives would never have entered clinical practice.' The sensitivity we quoted of 92% is achievable only by repeated examinations in wakefulness and sleep, and is far removed from the 50% obtained by the more usual single wake EEG. Conversely, the speci®city of 97% in patients with suspected intracranial disorders is a ®gure for waking records only. The increase in sensitivity from sleep recording is gained at the cost of reduced speci®city, but to what extent is unknown. The study of Beun et al. (1998), which appears to be the only substantial investigation of epileptiform patterns in multichannel sleep recordings from normal subjects, revealed a prevalence of 50%. This statement in turn should be quali®ed by the comment that the epileptiform patterns occurred very infrequently and a suitable threshold could probably be set to discriminate between subjects with and without epilepsy. Comparable data in non-epileptic patients, as opposed to normal subjects, appear to be totally lacking. Moreover, the very limited evidence on sensitivity and speci®city of the interictal EEG for investigating seizures in adults has no pediatric parallel. Given the choice of repeating inconclusive routine interictal recordings or capturing seizures by telemetry, it is all too common for the former strategy to be adopted (if such a haphazard approach may be digni®ed by the title of `strategy'). Clearly, the whole process of diagnostic EEG investigation of epilepsy requires further study, in both adults and children. It does no credit to the discipline of clinical electroencephalography that so little published information is yet available to provide an evidential basis for the most widely used clinical application of the EEG (Fowle and Binnie, 2000). In the meantime, where resources are abundant the ideal
1388-2457/00/$ - see front matter q 2000 Elsevier Science Ireland Ltd. All rights reserved.
www.elsevier.com/locate/clinph
Letters to the Editor Modern electroencephalography: its role in epilepsy management I was left rather confused by one of the main conclusions put forth by Drs. Binnie and Stefan in their otherwise excellent and comprehensive review of modern EEG in epilepsy (Binnie and Stefan, 1999). It is concluded that routine EEG examination `is of little value' for diagnostic screening because `the sensitivity of the waking interictal EEG for detecting epilepsy and its speci®city for distinguishing epilepsy from other episodic disorders are both very limited.' Nevertheless, in the section on diagnostic sensitivity the review of the relevant literature (including Dr. Binnie's own data) indicates a sensitivity of 92% for the demonstration of interictal epileptiform activity in epileptic patients with serial recordings. The next section goes on to describe a diagnostic speci®city ranging from 97% (in unselected subjects with and without cerebral dysfunction) to greater than 99.5% (in adults without known cerebral dysfunction). I understand, and agree with, a desire to discourage thoughtless `rule out epilepsy' referrals, and this desire is implicit in the authors' statement that the EEG is `of most utility when directed to the solution of appropriate and clearly de®ned problems.' However, an accurate diagnosis and classi®cation of epilepsy cannot be arrived at in all (or perhaps even most) patients on clinical grounds for a variety of reasons well described in the review. It seems to me that the diagnostic question most often faced by the clinician is simply: `Does this particular patient have epilepsy, and, if so, what type?' This is a clear problem for which diagnostic EEG screening would appear to be ideally suited to provide a solution. References Binnie CD, Stefan H. Modern electroencephalography: its role in epilepsy management. Clin Neurophysiol 1999;110:1671±1697.
Richard Wennberg
PII: S 1388-245 7(00)00287-X
Toronto Western Hospital, University of Toronto, Toronto, ON M5T 2S8, Canada
Reply to R. Wennberg There does not appear to be any fundamental difference of philosophy between Dr. Wennberg and ourselves, but a distinction does need to be made between the ideal of problem orientated investigation, which includes establishing the presence and type of epilepsy when these are in doubt, and `routine screening' by EEG. The reality of EEG practice in many European departments is close to that described by Hopkins and Scambler (1977), who commented: `¼it is remarkable that short paper records have been carried out for nearly 40 years with so little bene®t to patients or doctors. A biochemical test with so many false negatives would never have entered clinical practice.' The sensitivity we quoted of 92% is achievable only by repeated examinations in wakefulness and sleep, and is far removed from the 50% obtained by the more usual single wake EEG. Conversely, the speci®city of 97% in patients with suspected intracranial disorders is a ®gure for waking records only. The increase in sensitivity from sleep recording is gained at the cost of reduced speci®city, but to what extent is unknown. The study of Beun et al. (1998), which appears to be the only substantial investigation of epileptiform patterns in multichannel sleep recordings from normal subjects, revealed a prevalence of 50%. This statement in turn should be quali®ed by the comment that the epileptiform patterns occurred very infrequently and a suitable threshold could probably be set to discriminate between subjects with and without epilepsy. Comparable data in non-epileptic patients, as opposed to normal subjects, appear to be totally lacking. Moreover, the very limited evidence on sensitivity and speci®city of the interictal EEG for investigating seizures in adults has no pediatric parallel. Given the choice of repeating inconclusive routine interictal recordings or capturing seizures by telemetry, it is all too common for the former strategy to be adopted (if such a haphazard approach may be digni®ed by the title of `strategy'). Clearly, the whole process of diagnostic EEG investigation of epilepsy requires further study, in both adults and children. It does no credit to the discipline of clinical electroencephalography that so little published information is yet available to provide an evidential basis for the most widely used clinical application of the EEG (Fowle and Binnie, 2000). In the meantime, where resources are abundant the ideal
1388-2457/00/$ - see front matter q 2000 Elsevier Science Ireland Ltd. All rights reserved.