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A Proposed Diagnostic Scheme for People With Epileptic Seizures

An article by Jerome Engel, Jr on the proposed names for various epilepsies
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  ILAE Commission Report A Proposed Diagnostic Scheme for People with EpilepticSeizures and with Epilepsy: Report of the ILAE Task Force onClassification and Terminology Jerome Engel, Jr. UCLA School of Medicine, Los Angeles, California, U.S.A. The International League Against Epilepsy (ILAE)made a major contribution when it established standard-ized classifications and terminology for epileptic sei-zures and syndromes. This provided a universal vocabu-lary that not only facilitated communication among cli-nicians, but also established a taxonomic foundation forperforming quantitative clinical and basic research onepilepsy. Much, however, has changed since the adop-tion of the currently used Classification of Epileptic Sei-zures in 1981 (1) and the Classification of Epilepsies andEpileptic Syndromes in 1989 (2). Consequently, the Ex-ecutive Committee of the ILAE, which took office inJuly 1997, agreed that review and revision of the currentclassification system would be a priority for this Execu-tive term.A Task Force on Classification and Terminology wasappointed, which divided itself into four working groupsconcerned with Descriptive Terminology for IctalEvents; Seizures; Syndromes and Diseases; and Impair-ment. During the course of several meetings and vigor-ous e-mail discussions, the Task Force agreed that itwould not be possible to replace the current internationalclassifications with similar revised and updated classifi-cations that would be universally accepted and meet allthe clinical and research needs such a formal organiza-tional system would be expected to provide. Rather, theTask Force is proposing a diagnostic scheme that makesuse of standardized terminology and concepts to describeindividual patients (Table 1). Within this diagnosticscheme, a variety of approaches to classification are pos-sible, and some are presented here by way of exampleonly. The Task Force views the development of specificclassifications as a continuing work in progress. Flexibleand dynamic classifications will be revised periodicallybased not only on rapidly emerging new information, butalso on the resolution of problems that will inevitably beidentified through use. At this point, the proposal doesinclude several definitive changes in concepts and ter-minology (Table 2), and classifications are presented asexamples of what could be devised in the future. RATIONALE FOR THE PROPOSAL Although each new ILAE classification has repre-sented considerable effort on the part of acknowledgedexperts from many different countries, they have alwaysmet with a certain degree of resistance from the interna-tional epileptology community. This is because, in part,a rigid classification shapes the manner in which futuregenerations of clinical and basic neuroscientists think about epilepsy and epileptic phenomena, thereby influ-encing (perhaps unduly) clinical practice and research.For instance, in the current Classification of EpilepticSeizures, the division of partial seizures into “simple”and “complex” inappropriately created the impressionthat impairment of consciousness had certain mechanis-tic implications related to limbic system involvement.Confusion, and at times vociferous objections, resultedin part from the fact that the 1970 International Classi-fication of Epileptic Seizures had used the term “com-plex partial seizures” synonymously with “temporal lobeseizures” (3). Over the past two decades, detailed inves-tigations of the anatomic substrates of ictal semiology,based largely on work carried out in epilepsy surgerycenters, have strongly suggested that fundamentalmechanisms of certain limbic seizures are different fromthose of neocortical seizures, and that both can be asso-ciated with impairment of consciousness or not. Conse-quently, the designation of partial seizures as “simple,”or “complex,” has in the process lost meaningful preci-sion. Indeed, the 1981 Classification of Epileptic Sei- Accepted March 9, 2001.Address correspondence and reprint requests to Dr. J. Engel, Jr., atDepartment of Neurology, Reed Neurological Research Center, UCLASchool of Medicine, 710 Westwood Plaza, Los Angeles, CA 90095-1769, U.S.A. E-mail:  Epilepsia,  42 (6):796–803, 2001Blackwell Science, Inc.© International League Against Epilepsy 796   zures was purposely based purely on ictal phenomenol-ogy and associated EEG findings rather than anatomicsubstrates and pathophysiologic mechanisms, becauseinsufficient information was available at the time to per-mit the authors to do otherwise. It is the belief of theTask Force that adequate evidence now exists to permitcreation of a list of seizure types that represent diagnosticentities, as opposed to phenomenologic descriptions,based on known or presumed common anatomy andpathophysiology. Such diagnostic entities would, likesyndromes, have etiologic, therapeutic, and prognosticimplications, and could be used to supplement syndromicdiagnoses, or stand alone when syndromic diagnosescannot be made.The 1981 Classification of Epileptic Seizures also hasbeen criticized because it is not purely semiologic; posthoc etiologic information and EEG data are often re-quired to use it properly, and the dichotomy of “partial”versus “generalized” belies a need to avoid anatomicimplications. The Task Force believes that a purely de-scriptive phenomenologic approach to defining ictal se-miology has definite clinical value, and the new diag-nostic scheme proposed here includes a modification of a previously proposed classification of ictal phenomenol-ogy (4), as an option that can be used in detail whereappropriate.Similarly, the previous dichotomous classificationsbased on concepts of “partial” or “localization related”versus “generalized” abnormalities created the false im-pression that epileptic seizures, or epilepsy syndromes,were due to either localized disturbances in one hemi-sphere or disturbances involving the entire brain. A va-riety of conditions between focal and generalized epilep-togenic dysfunctions include diffuse hemispheric abnor-malities, multifocal abnormalities, and bilaterallysymmetrical localized abnormalities. Although conceptsof partial and generalized epileptogenicity have value,perhaps more with respect to ictal events than to syn-dromes, it is neither appropriate nor useful to attempt tocontain all seizures and syndromes within one or theother of these categorizations.The term partial itself has come under criticism be- TABLE 1.  Proposed diagnostic scheme for people withepileptic seizures and with epilepsy Epileptic seizures and epilepsy syndromes are to be described andcategorized according to a system that uses standardizedterminology, and that is sufficiently flexible to take into accountthe following practical and dynamic aspects of epilepsydiagnosis:1. Some patients cannot be given a recognized syndromicdiagnosis.2. Seizure types and syndromes change as new information isobtained.3. Complete and detailed descriptions of ictal phenomenologyare not always necessary.4. Multiple classification schemes can, and should, be designedfor specific purposes (e.g., communication and teaching;therapeutic trials; epidemiologic investigations; selection of surgical candidates; basic research; genetic characterizations).This diagnostic scheme is divided into five parts, or Axes,organized to facilitate a logical clinical approach to thedevelopment of hypotheses necessary to determine the diagnosticstudies and therapeutic strategies to be undertaken in individualpatients:Axis 1: Ictal phenomenology, from the Glossary of DescriptiveIctal Terminology, can be used to describe ictal events with anydegree of detail needed.Axis 2: Seizure type, from the List of Epileptic Seizures.Localization within the brain and precipitating stimuli for reflexseizures should be specified when appropriate.Axis 3: Syndrome, from the List of Epilepsy Syndromes, with theunderstanding that a syndromic diagnosis may not always bepossible.Axis 4: Etiology, from a Classification of Diseases FrequentlyAssociated with Epileptic Seizures or Epilepsy Syndromes whenpossible, genetic defects, or specific pathologic substrates forsymptomatic focal epilepsies.Axis 5: Impairment, this optional, but often useful, additionaldiagnostic parameter can be derived from an impairmentclassification adapted from the WHO ICIDH-2. TABLE 2.  Definitions of key terms  Epileptic seizure type:  An ictal event believed to represent a uniquepathophysiologic mechanism and anatomic substrate. This is adiagnostic entity with etiologic, therapeutic, and prognosticimplications. (new concept)  Epilepsy syndrome:  A complex of signs and symptoms that definea unique epilepsy condition. This must involve more than justthe seizure type: thus frontal lobe seizures  per se,  for instance,do not constitute a syndrome. (changed concept)  Epileptic disease:  A pathologic condition with a single specific,well-defined etiology. Thus progressive myoclonus epilepsy is asyndrome, but Unverricht–Lundborg is a disease. (new concept)  Epileptic encephalopathy:  A condition in which the epileptiformabnormalities themselves are believed to contribute to theprogressive disturbance in cerebral function. (new concept)  Benign epilepsy syndrome:  A syndrome characterized by epilepticseizures that are easily treated, or require no treatment, and remitwithout sequelae. (clarified concept)  Reflex epilepsy syndrome:  A syndrome in which all epilepticseizures are precipitated by sensory stimuli. Reflex seizures thatoccur in focal and generalized epilepsy syndromes that also areassociated with spontaneous seizures are listed as seizure types.Isolated reflex seizures also can occur in situations that do notnecessarily require a diagnosis of epilepsy. Seizures precipitatedby other special circumstances, such as fever or alcoholwithdrawal, are not reflex seizures. (changed concept) Focal seizures and syndromes:  Replaces the terms partial seizuresand localization-related syndromes. (changed terms) Simple and complex partial epileptic seizures:  These terms are nolonger recommended, nor will they be replaced. Ictal impairmentof consciousness will be described when appropriate forindividual seizures, but will not be used to classify specificseizure types. (new concept)  Idiopathic epilepsy syndrome:  A syndrome that is only epilepsy,with no underlying structural brain lesion or other neurologicsigns or symptoms. These are presumed to be genetic and areusually age dependent. (unchanged term) Symptomatic epilepsy syndrome:  A syndrome in which the epilepticseizures are the result of one or more identifiable structurallesions of the brain. (unchanged term) Probably symptomatic epilepsy syndrome:  Synonymous with, butpreferred to, the term cryptogenic, used to define syndromes thatare believed to be symptomatic, but no etiology has beenidentified. (new term)  ILAE REPORT ON CLASSIFICATION AND TERMINOLOGY 797   Epilepsia, Vol. 42, No. 6, 2001  cause it implies part of a seizure, or part of a syndrome,rather than a seizure or syndrome that begins in part of one hemisphere. For this reason, the 1989 Classificationof Epilepsies and Epileptic Syndromes replaced the termpartial with “localization-related.” This latter terminol-ogy has been cumbersome and is not consistently used.The Task Force is now proposing that the terms partialand localization-related be replaced with the older term“focal,” which remains in common use. It must bestrongly emphasized, however, that the term focal doesnot mean that the epileptogenic region is a small, well-delineated focus of neuronal pathology; focal seizures, aswell as focal syndromes, are almost always due to diffuse,and at times widespread, areas of cerebral dysfunction.Another change in terminology evident in this docu-ment is the omission of the words “convulsion” and“convulsive” in the list of epileptic seizure types andepilepsy syndromes. The Task Force thought that theseare nonspecific lay terms, and at times improperly used.Consequently it was agreed to be consistent, not only indescriptive ictal terminology, but also in naming epilep-tic seizure types and syndromes, to avoid these terms.For instance, the Task Force is proposing that the term“febrile convulsions” be replaced by “febrile seizures.”There also has been dissatisfaction with the terms “id-iopathic” and “cryptogenic.” Problems with the formerhave resulted from misunderstanding of the correct defi-nition of idiopathic, which means a disorder unto itself,sui generis, and not etiology unknown. Problems withthe latter have been due to an imprecision in definition;cryptogenic is usually used to designate conditions thatare not idiopathic, or are presumed to be symptomatic,when the etiology has not been determined, but it also isused by some for conditions in which it is not knownwhether they are idiopathic or symptomatic. The Task Force has been unable to find an acceptable alternative tothe term idiopathic, which, when used correctly, confersa useful taxonomic concept. The terms “benign” and“genetic” were discarded because not all idiopathic epi-lepsies are necessarily benign, and not all genetic epi-leptic conditions (e.g., the progressive myoclonus epi-lepsies) are idiopathic. Although the term “essential”also is used in medicine to convey the same meaning, theTask Force believes that most epileptologists have nowlearned to use the term idiopathic correctly, and thatthere is value in maintaining continuity. Consequently, itis recommended that the terms idiopathic and symptom-atic be retained, but that the term cryptogenic, althoughstill acceptable, be replaced by the more precise term“probably symptomatic.” Therefore, some epilepsy syn-dromes are referred to as either idiopathic or symptom-atic, but a dichotomous classification system that at-tempts to categorize all syndromes in this manner hasbeen avoided.Another important criticism of previous rigid syn-dromic classifications has been a failure to recognize thefact that some syndromes are well accepted, whereasothers are controversial, or lack sufficient data. Formallyrecognizing a syndrome by including it in an officialinternational classification may give it inappropriate le-gitimacy, whereas failing to recognize a syndrome in theofficial classification can discourage studies that are nec-essary to lead to its acceptance. Any official ILAE-sanctioned list of epilepsy syndromes must differentiatebetween universally accepted syndromes and those indevelopment, and must also be sufficiently flexible topermit additions and deletions of syndromes as new in-formation becomes available.The rapidly moving field of genetics has contributedgreatly in recent years to our understanding of manydiseases, including some epileptic disorders, but the re-lationship between genetic disturbances and phenotypicexpression remains complicated and poorly understood.Because a single, relatively well defined, idiopathicepilepsy syndrome can be due to more than one gene-tic abnormality, and different members of a family shar-ing a common genetic abnormality can have differentepilepsy syndromes, it was considered premature to at-tempt to classify epilepsy syndromes, to any greatextent, on the basis of specific genetic etiologies. Thereis no doubt, however, that in the near future, geneticclassifications of certain epilepsy syndromes will be-come possible, and that these classifications will haveconsiderable clinical value. It will be necessary for suchclassifications to include syndromes of families, in ad-dition to syndromes of individuals, and indeed theTask Force has included three such conditions in thecurrent recommended list of epilepsy syndromes (cf.Table 4): generalized epilepsy with febrile seizuresplus, familial focal epilepsy with variable foci, and idio-pathic generalized epilepsies with variable phenotypes.The first two of these are considered to be syndromesin development, and diagnosis would not be possiblewithout evidence of multiple affected family mem-bers. The third is a new concept, which remains underdiscussion. DESCRIPTION OF THE PROPOSAL The Task Force is asking the General Assembly toapprove a diagnostic scheme, rather than a fixed classi-fication, when it next meets in Buenos Aires in May2001. This diagnostic scheme is intended to provide thebasis for a standardized description of individual pa-tients, and consists of five levels, or Axes (Table 1). TheAxes are organized to facilitate a logical clinical ap-proach to the development of hypotheses necessary todetermine the diagnostic studies that should be per-formed, and the therapeutic strategies to be undertaken.The diagnostic scheme described here will be made up  J. ENGEL, JR.798   Epilepsia, Vol. 42, No. 6, 2001  of flexible and dynamic modules within which the Task Force will make periodic changes and updates as needed,with the approval of the Executive Committee. The Task Force is proposing that this diagnostic scheme includethe development of flexible, rather than rigid, classifica-tions, eliminating the need for the General Assembly,which meets only once every 2 years, to agree on everyrevision. Acceptance of this diagnostic scheme, there-fore, does not exclude the creation of various classifica-tion systems for seizures and syndromes, or the contin- TABLE 3.  Epileptic seizure types and precipitating stimuli for reflex seizures Self-limited seizure typesGeneralized seizuresTonic–clonic seizures (includes variations beginning with aclonic or myoclonic phase)Clonic seizuresWithout tonic featuresWith tonic featuresTypical absence seizuresAtypical absence seizuresMyoclonic absence seizuresTonic seizuresSpasmsMyoclonic seizuresEyelid myocloniaWithout absencesWith absencesMyoclonic atonic seizuresNegative myoclonusAtonic seizuresReflex seizures in generalized epilepsy syndromesFocal seizuresFocal sensory seizuresWith elementary sensory symptoms (e.g., occipital andparietal lobe seizures)With experiential sensory symptoms (e.g.,temporoparietooccipital junction seizures)Focal motor seizuresWith elementary clonic motor signsWith asymmetric tonic motor seizures (e.g., supplementarymotor seizures)With typical (temporal lobe) automatisms (e.g., mesialtemporal lobe seizures)With hyperkinetic automatismsWith focal negative myoclonusWith inhibitory motor seizuresGelastic seizuresHemiclonic seizuresSecondarily generalized seizuresReflex seizures in focal epilepsy syndromesContinuous seizure typesGeneralized status epilepticusGeneralized tonic–clonic status epilepticusClonic status epilepticusAbsence status epilepticusTonic status epilepticusMyoclonic status epilepticusFocal status epilepticusEpilepsia partialis continua of KojevnikovAura continuaLimbic status epilepticus (psychomotor status)Hemiconvulsive status with hemiparesisPrecipitating stimuli for reflex seizuresVisual stimuliFlickering light: color to be specified when possiblePatternsOther visual stimuliThinkingMusicEatingPraxisSomatosensoryProprioceptiveReadingHot waterStartle TABLE 4.  Epilepsy syndromes and related conditions Benign familial neonatal seizuresEarly myoclonic encephalopathyOhtahara syndrome a Migrating partial seizures of infancyWest syndromeBenign myoclonic epilepsy in infancyBenign familial infantile seizuresBenign infantile seizures (nonfamilial)Dravet’s syndromeHH syndrome a Myoclonic status in nonprogressive encephalopathiesBenign childhood epilepsy with centrotemporal spikesEarly-onset benign childhood occipital epilepsy (Panayiotopoulostype)Late-onset childhood occipital epilepsy (Gastaut type)Epilepsy with myoclonic absencesEpilepsy with myoclonic–astatic seizuresLennox–Gastaut syndromeLandau–Kleffner syndrome (LKS)Epilepsy with continuous spike-and-waves during slow-wave sleep(other than LKS)Childhood absence epilepsyProgressive myoclonus epilepsiesIdiopathic generalized epilepsies with variable phenotypesJuvenile absence epilepsyJuvenile myoclonic epilepsyEpilepsy with generalized tonic–clonic seizures onlyReflex epilepsiesIdiopathic photosensitive occipital lobe epilepsyOther visual sensitive epilepsiesPrimary reading epilepsyStartle epilepsyAutosomal dominant nocturnal frontal lobe epilepsyFamilial temporal lobe epilepsies a Generalized epilepsies with febrile seizures plus a Familial focal epilepsy with variable fociSymptomatic (or probably symptomatic) focal epilepsiesLimbic epilepsiesMesial temporal lobe epilepsy with hippocampal sclerosisMesial temporal lobe epilepsy defined by specific etiologiesOther types defined by location and etiologyNeocortical epilepsiesRasmussen syndromeOther types defined by location and etiologyConditions with epileptic seizures that do not require a diagnosis of epilepsyBenign neonatal seizuresFebrile seizuresReflex seizuresAlcohol-withdrawal seizuresDrug or other chemically induced seizuresImmediate and early posttraumatic seizuresSingle seizures or isolated clusters of seizuresRarely repeated seizures (oligoepilepsy) a Syndromes in development.  ILAE REPORT ON CLASSIFICATION AND TERMINOLOGY 799  Epilepsia, Vol. 42, No. 6, 2001
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