You are in: eMedicine Specialties > Neurology > EEG Atlas: Encephalopathic Patterns III - Miscellaneous PatternsArticle Last Updated: *ba 0, 0AUTHOR AND EDITOR INFORMATIONSection 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: encephalopathic patterns, alpha coma, beta coma, spindle coma, triphasic waves, cerebral function, diffuse brain dysfunction, diffuse encephalopathy, brain function INTRODUCTIONSection 2 of 6
  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 more severe patterns (ie, periodic patterns, such as burst-suppression, background suppression, and electrocerebral inactivity) are discussed in EEG Atlas: Encephalopathic Patterns II - More Severe Patterns. This article reviews less common encephalopathic patterns, including alpha coma, beta coma, spindle coma, and triphasic waves. Patient Education For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education article Electroencephalography (EEG). WAVEFORM DESCRIPTIONSSection 3 of 6
Unusual special patterns observed in comatose patients include alpha coma (Image 1), beta coma (Image 2), and spindle coma (Image 3).
Triphasic waves are frontally positive sharp transients, usually of greater than 70 microvolts amplitude (see Image 4). The positive phase usually is preceded and followed by a smaller negative waveform. As a rule, the first negative wave is of higher amplitude than the second. They are bilateral and occur in bursts of repetitive waves at 1-3 Hz. No reactivity is the rule, and often an anterior-posterior temporal lag can be observed. The largest deflection is usually frontal, and in ear referential montage the time lag is usually not present. The usual clinical correlate of triphasic waves is a metabolic or other diffuse encephalopathy. Thus, a triphasic morphology (while necessary) is not sufficient to classify a record as "triphasic waves." CLINICAL CORRELATIONSection 4 of 6
Alpha coma, beta coma, and spindle coma are infrequent. They are, like all the encephalopathic patterns, nonspecific in regard to etiology, although anoxia often is associated with alpha coma and drugs with beta coma. They are generally indicative of a severe degree of encephalopathy. Reactivity is a good prognostic factor. In fact, some investigators, including the author, do not classify a record as alpha or spindle coma if it is reactive. Triphasic waves classically are associated with hepatic encephalopathy. However, they are not specific and can be observed in uremic encephalopathy and even other types of metabolic derangements. Many other patterns can have a triphasic morphology. Like periodic patterns, triphasic waves quite often are observed in the context of nonconvulsive status epilepticus. Often the decision whether to consider triphasic waves ictal must rely on the clinical information or the response to anticonvulsant treatment. MULTIMEDIASection 5 of 6
REFERENCESSection 6 of 6
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