Excerpt from Focal EEG Waveform Abnormalities
Synonyms, Key Words, and Related Terms: electroencephalogram, EEG, transient EEG abnormalities, epileptiform patterns, spikes, sharp waves, continuous focal abnormalities, alterations of ongoing EEG background activity, attenuation, enhancement, focal slow-wave abnormalities, periodic EEG patterns, rhythmic and repetitive sharp wave or spike patterns, epileptiform discharges, epileptiform EEG patterns, EEG background rhythms, focal slowing, periodic EEG patterns, periodic lateralized epileptiform discharges, PLEDs, bilateral independent periodic lateralized epileptiform discharges, BIPLEDs
The electroencephalogram (EEG) is a mainstay of diagnosis for patients with epilepsy, suspected seizures, or impaired consciousness. Prior to the availability of cerebral imaging techniques, such as computed tomography (CT) scanning and magnetic resonance imaging (MRI), EEG was critical for diagnosis of mass lesions in the cerebral hemispheres. For example, in a comatose patient whose EEG manifested decreased amplitude over one cerebral hemisphere, subdural hematoma was strongly suspected. Such EEG diagnosis of cerebral lesions is no longer necessary. Nonetheless, EEG is a critical tool for defining the physiology of focal abnormalities of the cerebrum; such physiologic foci may have no neuroimaging correlates. EEG can further define the clinical significance of regions with subtle or undetected changes on CT scan or MRI.
Focal EEG abnormalities may be either transient or continuous. Transient EEG abnormalities include epileptiform patterns, such as spikes or sharp waves; these must be distinguished from other transient patterns representing benign variants that may be mistaken for pathological findings. Continuous focal abnormalities include alterations of ongoing EEG background activity (either attenuation or enhancement), focal slow-wave abnormalities, or periodic EEG patterns that consist of rhythmic and repetitive sharp wave or spike patterns. Each of these types of abnormalities typically is associated with underlying focal pathology. More widespread central nervous system (CNS) physiologic derangements, such as those due to metabolic disturbances, also can occasionally produce such focal EEG abnormalities; most often, these are superimposed on a structural abnormality, though the lesion may not be visualized on brain imaging.
Patient Education
For excellent patient education resources, visit eMedicine's Procedures Center. Also, see eMedicine's patient education article Electroencephalography (EEG).
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