You are in: eMedicine Specialties > Neurology > Electroencephalography Atlas Localization-Related Epilepsies on EEGArticle Last Updated: Sep 10, 2008AUTHOR AND EDITOR INFORMATIONSection 1 of 7
  Author: Selim R Benbadis, MD, Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida School of Medicine, Tampa General Hospital Selim R Benbadis is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, and American Medical Association Coauthor(s): Diego Rielo, MD, Staff Physician, Department of Neurology, Memorial Hospital West, Memorial Hospital Pembroke, Memorial Healthcare Editors: Leslie Huszar, MD, Consulting Staff, Department of Neurology, Indian River Memorial Hospital; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Norberto Alvarez, MD, Assistant Professor, Department of Neurology, Harvard Medical School; Consulting Staff, Department of Neurology, Boston Children's Hospital; Matthew J Baker, MD, Consulting Staff, Collier Neurologic Specialists, Naples Community Hospital; Helmi L Lutsep, MD, Professor, Department of Neurology, Oregon Health and Science University; Associate Director, Oregon Stroke Center Author and Editor Disclosure Synonyms and related keywords: EEG atlas, localization-related epilepsies, focal epilepsies, partial epilepsies, spikes and sharp waves, benign focal epilepsy of childhood, autosomal dominant nocturnal frontal lobe epilepsy, ADNFLE, benign childhood epilepsy with centrotemporal spikes, BECTS, cryptogenic focal epilepsies INTRODUCTIONSection 2 of 7
  The International Classification of Epileptic Syndromes and Epilepsies1 classifies the epilepsies along 2 dichotomies: partial (ie, localization-related) versus generalized, and idiopathic versus cryptogenic or symptomatic. This double dichotomy conveniently allows presentation of the epilepsy classification in a simple table, as follows: Classification of the Epilepsies (Adapted from Tich and Pereon, 19992)
*ADNFLE - Autosomal dominant nocturnal frontal lobe epilepsy The term idiopathic is often misunderstood in this setting and requires clarification. Whereas the term idiopathic usually means "of unknown cause," idiopathic epilepsies are not truly of unknown cause (this confusing terminology will most likely be corrected in the upcoming ILAE classification system3). Idiopathic epilepsies are determined genetically and have no apparent structural cause, with seizures as the only manifestation of the condition. Findings of the neurologic examination and imaging studies are normal, and EEG is normal other than the epileptiform abnormalities. In some syndromes, the genetic substrate has even been identified. Most idiopathic epilepsies are generalized, but a few are focal. Nonidiopathic epilepsies are by definition not genetic, although some may be associated with a minor genetic predisposition; they 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 is subtle: symptomatic means that the etiology is known, while cryptogenic means that an underlying etiology is apparent but cannot be documented objectively. Thus, the boundary between the two is largely dependent on the capabilities of our diagnostic and imaging techniques. This review discusses EEG findings in the localization-related (also known as focal or partial) epilepsies. WAVEFORM DESCRIPTIONSSection 3 of 7
Spikes and sharp waves are sharp transients that have a strong association with epilepsy. The 2 are distinguished only by their duration (spikes <70 ms, sharp waves 70-200 ms), but they have no differences in terms of clinical significance. Several characteristics distinguish these from benign epileptiform variants (see article EEG Atlas: Focal (Nonepileptic) Abnormalities), including high amplitudes, which make them "stand out" from ongoing background activity, and aftergoing slow waves, which give the appearance of their "disrupting" background activity (see Media files 1-6). CLINICAL CORRELATIONSection 4 of 7
Idiopathic localization-related epilepsies Benign focal epilepsy of childhood is the main localization-related epilepsy that is idiopathic. Two varieties have been well described and are in the 1989 ILAE classification: centrotemporal and occipital. A third type has been described more recently: autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE). Benign childhood epilepsy with centrotemporal spikes (BECTS) is by far the more common. Age of onset is between 4 and 12 years (peak age 8-9 y). Seizures are simple partial with motor symptoms involving the face, and they tend to occur during sleep or on awakening. Though these focal seizures are the most characteristic seizure types in BECTS, they can be quite subtle and are missed easily, so that the most common mode of presentation is a (secondary) generalized tonic-clonic seizure. As with all idiopathic epilepsy syndromes, neurologic examination findings are normal. EEG findings are characteristic, with stereotyped centrotemporal sharp waves that have a characteristic morphology. They are activated markedly by non–rapid eye movement (NREM) sleep, often occur in repetitive bursts, and can be bilateral and independent. Notably, the interictal sharp waves of BECTS often occur in asymptomatic children. In fact, only a minority of children with these discharges may have seizures. Childhood epilepsy with occipital paroxysms is less common and less consistently benign. It shares all the characteristics of an idiopathic syndrome (ie, normal findings on examination, intelligence quotient [IQ] testing, and neuroimaging studies). Age of onset is 4-8 years. Seizures are rare and primarily nocturnal, and often involve visual symptoms. Sharp waves have a maximum occipital negativity, often occur in long bursts of spike-wave complexes, and are activated markedly by eye closure. ADNFLE is a recently described genetic localization-related epilepsy. Several mutations of the neuronal nicotinic acetylcholine receptor alpha4 subunit have been identified in association with this epilepsy. It has the expected features of idiopathic (ie, genetic) epilepsies, including onset early in life and normal imaging findings. Seizures are nocturnal and occur in clusters, mimicking parasomnias. They are mostly brief tonic seizures and rare (secondarily) generalized tonic-clonic convulsions, often preceded by a nonspecific aura. Interictal EEG may show epileptiform discharges with a frontal predominance, often seen only in sleep. Ictal EEG does not always show definite ictal discharges. Thus, the electroclinical features of ADNFLE are not different from those of symptomatic or cryptogenic frontal lobe epilepsy. Since the genetic findings are variable (ie, locus heterogeneity), its definite diagnosis is largely one of exclusion. Cryptogenic focal epilepsies This is by far the most common type of adult-onset epilepsy. By definition, seizures arise from a localized region of the brain. If the cause is found, they are said to be symptomatic. If imaging study findings are normal, the cause remains presumptive and they are said to be cryptogenic. As stated already, the boundary between the two is largely dependent on our diagnostic and imaging techniques, and etiologies such as low-grade tumors, hippocampal sclerosis, and subtle cortical dysplasias are identified more and more often owing to advances in neuroimaging. Clinically, seizures may be simple partial or complex partial, with or without secondary generalization. Interictal EEG shows focal spikes or sharp waves, and ictal EEG shows a focal or regional discharge at onset. The main clinical entities are mesiotemporal lobe epilepsy, neocortical focal epilepsies, and hemispheric syndromes. PATIENT EDUCATIONSection 5 of 7
For excellent patient education resources, visit eMedicine's Procedures Center and Brain and Nervous System Center. Also, see eMedicine's patient education articles Electroencephalography (EEG) and Epilepsy. MULTIMEDIASection 6 of 7
REFERENCESSection 7 of 7
Localization-Related Epilepsies on EEG excerpt Article Last Updated: Sep 10, 2008 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
