Generalized Epilepsies on EEG

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The International Classification of Epileptic Syndromes and Epilepsies [1] classifies the epilepsies along 2 dichotomies: (1) partial (ie, localization-related) versus generalized and (2) idiopathic versus cryptogenic or symptomatic. This double dichotomy conveniently allows the epilepsy classification system to be presented in a simple and clear manner (see the Table below).

Table. Classification of the Epilepsies (Adapted from Tich and Pereon, 1999 [2] ) (Open Table in a new window)

 

Generalized

Localization-related

Idiopathic

(genetic)

Childhood absence epilepsy

Juvenile absence epilepsy

Juvenile myoclonic epilepsy

Epilepsy with grand-mal seizures on awakening

Other idiopathic generalized epilepsies

Benign focal epilepsy of childhood (2 types)

ADNFLE*

Primary reading epilepsy

Symptomatic

or cryptogenic

West syndrome

Lennox-Gastaut syndrome

Other symptomatic generalized epilepsies

Mesiotemporal lobe epilepsy

Neocortical focal epilepsy

*ADNFLE – Autosomal dominant nocturnal frontal lobe epilepsy

The term idiopathic often is misunderstood in this setting and requires clarification. Whereas the term idiopathic in medicine usually means “of unknown cause,” idiopathic epilepsies are not truly of unknown cause; this confusing terminology will most likely be corrected in the upcoming International League Against Epilepsy (ILAE) classification system. [3]

In epilepsy, idiopathic seizures are genetically determined and have no apparent structural cause, with seizures as the only manifestation of the condition. Findings of the neurologic examination and neuroimaging studies are normal, and electroencephalographic (EEG) findings also are normal, aside from the epileptiform abnormalities. In some syndromes, the genetic substrate has even been identified. Most idiopathic epilepsies are generalized, but a few genetic epilepsies are focal.

Nonidiopathic epilepsies, by definition, are not genetic (though some may be associated with a minor genetic predisposition) but are the result of a brain insult or lesion. If the damage is focal, it results in a localization-related epilepsy; if it is diffuse, it results in a generalized epilepsy.

The difference between symptomatic and cryptogenic in this context is subtle: to say that an epilepsy is symptomatic means that the etiology is known, whereas to say that it is cryptogenic means that an underlying etiology is apparent but cannot be documented objectively. Thus, the boundary between the 2 is largely dependent on our diagnostic and imaging techniques.

This review discusses EEG findings in the generalized epilepsies. [20, 21, 22] Go to Epilepsy and Seizures for an overview of this topic.

For patient education resources, see the Brain and Nervous System Center.

Spikes and sharp waves are sharp transients that have a strong association with epilepsy. They can be distinguished by their duration (spikes, < 70 ms; sharp waves, 70-200 ms) but have essentially the same clinical significance. Several characteristics distinguish these from benign epileptiform variants, including a high amplitude, which makes them stand out from ongoing background activity, and aftergoing slow waves, which give the appearance of disrupting or disturbing background activity (see the images below).

Spike-wave complexes (SWCs) are the repetitive occurrence of a spike followed by a slow wave. Since any significant spike or sharp wave usually is followed by a slow wave (see above), a run of 3 seconds is required to classify a record as SWC, as opposed to the categories already mentioned (spike or sharp wave). SWCs can be divided further into 2 more specific types: 3-Hz SWCs and slow SWCs.

The 3-Hz SWC pattern is characterized by a frequency of 2.5-4 Hz and a very monomorphic (perfectly regular) morphology. It occurs in very discrete bursts, and between bursts the EEG is normal (see the image below).

Slow SWCs are not only slower than 3-Hz SWCs (< 2.5 Hz) but also more irregular—that is, less monomorphic (see the images below). Bursts are less discrete than with 3-Hz SWCs, and between bursts, other abnormalities are seen in symptomatic or cryptogenic epilepsies of the Lennox-Gastaut type.

Generalized epileptiform discharges (ie, spikes, sharp waves, SWCs) are usually maximal in the frontal regions, with typical phase reversals at the F3 and F4 electrodes (see the image below).

Polyspikes are multiple repetitive spikes occurring at about 20 Hz (see the image below). They are associated with idiopathic generalized epilepsies, most typically juvenile myoclonic epilepsy.

Hypsarrhythmia is defined as continuous (during wakefulness), high-amplitude (>200 Hz), generalized polymorphic slowing with no organized background and multifocal spikes (see the images below). [4] It is commonly associated with West syndrome.

Generalized paroxysmal fast activity (GPFA) consists of bursts of fast (10 Hz) activity and typically is associated with tonic seizures. [5] Electrodecrement consists of abrupt attenuation (flattening) of background activity, often preceded by a high-amplitude transient (see the image below). This typically is associated with infantile spasms or atonic seizures.

Idiopathic generalized epilepsies, formerly called primary generalized epilepsies, are the best-known group of idiopathic epilepsies. [6, 7] They epitomize the meaning of the term “idiopathic”: genetic basis, normal neurologic examination findings, and normal intelligence.

Electroencephalography (EEG) shows generalized epileptiform discharges and may show photosensitivity. Seizure types include generalized tonic-clonic (GTC), absence, and myoclonic. Accordingly, EEG typically shows generalized spikes or sharp waves, 3-Hz or faster spike-wave complexes (SWCs; clinically associated with absence seizures), and polyspikes (clinically associated with myoclonic seizures). The EEG is normal (ie, no abnormal slowing) except for the epileptiform abnormalities.

Within the group of idiopathic generalized epilepsies, distinct entities are distinguished, primarily on the basis of predominant seizure type(s) and age of onset. Some syndromes are very well individualized, whereas others have less clear boundaries. [8, 9] The major and well-defined types of idiopathic generalized epilepsies include childhood absence epilepsy, [10, 11, 12, 13] juvenile myoclonic epilepsy, [14, 15, 16] and epilepsy with grand mal seizures (sometimes referred to as grand mal on awakening).

Symptomatic or cryptogenic epilepsies are associated with diffuse brain dysfunction. The cause may be known (symptomatic), such as anoxic birth injury or a metabolic or chromosomal defect, or it may be unknown (cryptogenic).

Accordingly, clinical evidence of diffuse brain dysfunction is usually present, either intellectual (eg, developmental delay or mental retardation) or motor (eg, developmental delay or cerebral palsy). Similarly, the EEG shows evidence of diffuse brain dysfunction in addition to the epileptiform abnormalities, in the form of slowing. The clinical and EEG manifestations are not specific as to etiology; they vary tremendously with age and thus are said to be age dependent.

West syndrome is the phenotype of symptomatic or cryptogenic generalized epilepsy in the first year of life and is characterized by infantile spasms, hypsarrhythmia, and developmental delay. [17] It is an age-specific response of the immature brain to a nonspecific focal or generalized insult. The age of onset peaks between 3 and 7 months.

Lennox-Gastaut syndrome (LGS) has an early childhood onset (age, 1-8 y) and consists of multiple seizure types, mental retardation, and typical EEG findings dominated by generalized slow SWCs. [18] Seizure types include atypical absences, tonic, atonic, myoclonic, and GTC seizures. The atonic, myoclonic, tonic, and GTC seizures of LGS frequently result in unprotected falls (referred to as “drop attacks”) with injury.

Besides the classic EEG pattern of generalized slow SWC, other frequent but less specific EEG findings include background slowing, generalized slowing, and multifocal spikes. During sleep, the EEG may show polyspikes and slow waves. Another typical feature of LGS is generalized paroxysmal fast (>10 Hz) activity (GPFA) during sleep. Many patients with symptomatic generalized epilepsy do not meet all the criteria for LGS.

International League Against Epilepsy, Commission on Classification and Terminol. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia. 1989 Jul-Aug. 30(4):389-99. [Medline].

Tich SN, Pereon Y. Semiological seizure classification. Epilepsia. 1999 Apr. 40(4):531. [Medline].

Engel J Jr. Classifications of the International League Against Epilepsy: time for reappraisal. Epilepsia. 1998 Sep. 39(9):1014-7. [Medline].

Hrachovy RA, Frost JD Jr, Kellaway P. Hypsarrhythmia: variations on the theme. Epilepsia. 1984 Jun. 25(3):317-25. [Medline].

Brenner RP, Atkinson R. Generalized paroxysmal fast activity: electroencephalographic and clinical features. Ann Neurol. 1982 Apr. 11(4):386-90. [Medline].

Benbadis SR, Luders HO. Generalized epilepsies. Neurology. 1996 Apr. 46(4):1194-5. [Medline].

Reutens DC, Berkovic SF. Idiopathic generalized epilepsy of adolescence: are the syndromes clinically distinct?. Neurology. 1995 Aug. 45(8):1469-76. [Medline].

Benbadis SR, Luders HO. Epileptic syndromes: an underutilized concept. Epilepsia. 1996 Nov. 37(11):1029-34. [Medline].

Benbadis SR, Wyllie E. Pediatric epilepsy syndromes. Levin KH, Luders HO, eds. Comprehensive Clinical Neurophysiology. Philadelphia, Pa: WB Saunders; 2000. 468-80.

Appleton RE, Beirne M. Absence epilepsy in children: the role of EEG in monitoring response to treatment. Seizure. 1996 Jun. 5(2):147-8. [Medline].

Berkovic SF, Andermann F, Andermann E, et al. Concepts of absence epilepsies: discrete syndromes or biological continuum?. Neurology. 1987 Jun. 37(6):993-1000. [Medline].

Holmes GL, McKeever M, Adamson M. Absence seizures in children: clinical and electroencephalographic features. Ann Neurol. 1987 Mar. 21(3):268-73. [Medline].

Loiseau P, Duche B, Pedespan JM. Absence epilepsies. Epilepsia. 1995 Dec. 36(12):1182-6. [Medline].

Grunewald RA, Panayiotopoulos CP. Juvenile myoclonic epilepsy. A review. Arch Neurol. 1993 Jun. 50(6):594-8. [Medline].

Lancman ME, Asconape J, Brotherton T, et al. Juvenile myoclonic epilepsy: an underdiagnosed syndrome. J Epilepsy. 1995. 8:215-218.

Lancman ME, Asconape JJ, Penry JK. Clinical and EEG asymmetries in juvenile myoclonic epilepsy. Epilepsia. 1994 Mar-Apr. 35(2):302-6. [Medline].

Lombroso CT. A prospective study of infantile spasms: clinical and therapeutic correlations. Epilepsia. 1983 Apr. 24(2):135-58. [Medline].

Markand ON. Slow spike-wave activity in EEG and associated clinical features: often called ‘Lennox’ or “Lennox-Gastaut’ syndrome. Neurology. 1977 Aug. 27(8):746-57. [Medline].

Thomas P, Beaumanoir A, Genton P, Dolisi C, Chatel M. De novo’ absence status of late onset: report of 11 cases. Neurology. 1992 Jan. 42(1):104-10. [Medline].

Seneviratne U, Hepworth G, Cook M, D’Souza W. Atypical EEG abnormalities in genetic generalized epilepsies. Clin Neurophysiol. 2015 Jun 19. [Medline].

Kay B, Szaflarski JP. EEG/fMRI contributions to our understanding of genetic generalized epilepsies. Epilepsy Behav. 2014 May. 34:129-35. [Medline].

Rosenow F, Klein KM, Hamer HM. Non-invasive EEG evaluation in epilepsy diagnosis. Expert Rev Neurother. 2015 Apr. 15 (4):425-44. [Medline].

 

Generalized

Localization-related

Idiopathic

(genetic)

Childhood absence epilepsy

Juvenile absence epilepsy

Juvenile myoclonic epilepsy

Epilepsy with grand-mal seizures on awakening

Other idiopathic generalized epilepsies

Benign focal epilepsy of childhood (2 types)

ADNFLE*

Primary reading epilepsy

Symptomatic

or cryptogenic

West syndrome

Lennox-Gastaut syndrome

Other symptomatic generalized epilepsies

Mesiotemporal lobe epilepsy

Neocortical focal epilepsy

*ADNFLE – Autosomal dominant nocturnal frontal lobe epilepsy

Selim R Benbadis, MD Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, Tampa General Hospital, University of South Florida Morsani College of Medicine

Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, American Medical Association

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Acorda, Livanova, Eisai, Greenwich, Lundbeck, Neuropace, Sunovion, Upsher-Smith.<br/>Serve(d) as a speaker or a member of a speakers bureau for: Livanova, Eisai, Greenwich, Lundbeck, Neuropace, Sunovion.<br/>Received research grant from: Acorda, Livanova, Greenwich, Lundbeck, Sepracor, Sunovion, UCB, Upsher-Smith.

Diego Antonio Rielo, MD Staff Physician, Department of Neurology, Memorial Hospital West, Memorial Healthcare

Diego Antonio Rielo, MD is a member of the following medical societies: American Academy of Neurology

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Norberto Alvarez, MD Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children’s Hospital; Medical Director, Wrentham Developmental Center

Norberto Alvarez, MD is a member of the following medical societies: American Academy of Neurology, American Epilepsy Society, Child Neurology Society

Disclosure: Nothing to disclose.

Helmi L Lutsep, MD Professor and Vice Chair, Department of Neurology, Oregon Health and Science University School of Medicine; Associate Director, OHSU Stroke Center

Helmi L Lutsep, MD is a member of the following medical societies: American Academy of Neurology, American Stroke Association

Disclosure: Medscape Neurology Editorial Advisory Board for: Stroke Adjudication Committee, CREST2; Executive Committee for the NINDS-funded DEFUSE3 Trial; Physician Advisory Board for Coherex Medical.

Generalized Epilepsies on EEG

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