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EEG Atlas: Encephalopathic Patterns II - More Severe Patterns
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AUTHOR AND EDITOR INFORMATION
Section 1 of 6  
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; Nicholas Y Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants
Author and Editor Disclosure
Synonyms and related keywords:
brain death, ECI, electrocerebral inactivity, ECI, periodic patterns, burst-suppression, periodicity, cerebral function, brain function
Since EEG is a test of cerebral function, diffuse (generalized) abnormal patterns are by definition indicative of diffuse brain dysfunction (ie, diffuse encephalopathy). Generalized slowing is discussed in EEG Atlas: Encephalopathic Patterns I - Generalized Slowing, and other encephalopathic patterns are discussed in EEG Atlas: Encephalopathic Patterns III - Miscellaneous Patterns.
This article reviews patterns that generally are considered the next level of severity beyond generalized slowing. These patterns include periodic patterns (such as burst-suppression), background suppression, and electrocerebral inactivity (ECI).
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- Periodic patterns (Image 1): Discharges occur at regular intervals (ie, periodicity). The discharges are typically complex and multiphasic and often are epileptiform in morphology. Thus, they are like periodic lateralizing epileptiform discharges (PLEDs) except that, instead of being lateralized, they are generalized. They sometimes are referred to as generalized periodic epileptiform discharges (GPEDs). Their periodicity rather than their morphology sets them apart as a unique and clinically useful entity (as is true for PLEDs). By contrast, the term bi-PLEDs usually refers to periodic discharges that are bihemispheric but asynchronous (ie, independent).
- Burst-suppression pattern (Image 2): This subtype of periodic pattern consists of bursts of activity (mixture of sharp and slow waves) periodically interrupted by episodes of suppression (activity <10 µV). Typically, the episodes of suppression are longer (typically 5-10 s) than the bursts of activity (typically 1-3 s).
- Background suppression: This is a "nearly flat" EEG, with very low voltage activity ( <10 µV) and no reactivity, but the activity is still too large to meet criteria for ECI.
- Electrocerebral inactivity (Image 3): ECI is defined by no activity greater than 2 µV; to support a diagnosis of brain death while avoiding "overcalling" brain death, ECI must be recorded according to strict guidelines. These requirements specify recording time, double interelectrode distances, testing reactivity, and the integrity of the system. (See Generalized EEG Waveform Abnormalities for the ECI Guidelines of the American Clinical Neurophysiology Society.)
- As usual, these severe encephalopathic patterns are completely nonspecific as to etiology but represent extremely severe degrees of diffuse encephalopathy. Because sedative medications can cause or aggravate these abnormalities, careful interpretation is warranted when reading these patterns. These patterns are indicative of very severe brain dysfunction if sedative medications can be excluded with certainty as their cause.
- Periodic patterns, including burst-suppression patterns, are somewhat more common in anoxic injuries than in other systemic disturbances. Periodic patterns can be induced by high doses of sedatives such as barbiturates, benzodiazepines, or propofol. In fact, burst-suppression pattern is typically the goal and the method used to titrate doses of anesthetics for treatment of refractory status epilepticus.
- In the appropriate clinical context, certain periodic patterns can suggest and support the diagnoses of Creutzfeldt-Jakob disease (CJD) and subacute sclerosing panencephalitis (SSPE). Classically, the periodicity for CJD is approximately 1-2 seconds, whereas it is much longer in SSPE (approximately 4-10 s).
- Rhythmicity or periodicity is one of the hallmarks of electrographic seizures; thus, periodic patterns quite often are observed in the context of nonconvulsive status epilepticus. Often the decision whether to consider a periodic pattern ictal must rely on clinical information or the response to anticonvulsant treatment.
- ECI is supportive of a clinical diagnosis of brain death. Remembering and emphasizing that brain death is a clinical diagnosis is important. Contrary to a common misconception, EEG is not required for the diagnosis of brain death and is considered only as a supportive test.
| Media file 1:
Classification: periodic pattern, generalized. The periodicity here is approximately 1 second. |
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Media type: Rhythm Strip
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| Media file 2:
Classification: burst-suppression. Note that this is a 15-second segment, to show the periods of suppression (4-5 s) separated by the bursts. Suppression periods are characterized by activity less than 10 mV. |
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Media type: Rhythm Strip
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| Media file 3:
Classification: electrocerebral inactivity. The recording demonstrates no cerebral activity greater than 2 mV. Given the high sensitivity (2 mV/mm), a combination of ECG and 60-Hz artifact often is present, as observed here. |
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Media type: Rhythm Strip
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- American EEG Society. Guideline three: minimum technical standards for EEG recording in suspected cerebral death. American Electroencephalographic Society. J Clin Neurophysiol. Jan 1994;11(1):10-3. [Medline].
- Benbadis SR. Introduction to EEG. In: Lee-Chiong T, ed. Sleep: A Comprehensive Handbook. Hoboken, NJ: Wiley & Sons; 2006:. 989-1024.
- Geller E. Generalized disturbances of brain function: encephalopathies, coma, degenerative diseases, and brain death. In: Levin KH, Luders HO, eds. Comprehensive Clinical Neurophysiology. Philadelphia, Pa: WB Saunders;2000:438-55.
- Husain AM, Mebust KA, Radtke RA. Generalized periodic epileptiform discharges: etiologies, relationship to status epilepticus, and prognosis. J Clin Neurophysiol. Jan 1999;16(1):51-8. [Medline].
- Levin KH, Luders HO, eds. Comprehensive Clinical Neurophysiology. Philadelphia, Pa: WB Saunders;2000.
- Luders H, Noachtar S, eds. Atlas and Classification of Electroencephalography. Philadelphia, Pa: WB Saunders;2000.
- Smith SJ. EEG in the diagnosis, classification, and management of patients with epilepsy. J Neurol Neurosurg Psychiatry. Jun 2005;76 Suppl 2:ii2-7. [Medline].
- Smith SJ. EEG in neurological conditions other than epilepsy: when does it help, what does it add?. J Neurol Neurosurg Psychiatry. Jun 2005;76 Suppl 2:ii8-12. [Medline].
EEG Atlas: Encephalopathic Patterns II - More Severe Patterns excerpt Article Last Updated: *ba 0, 0
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