What is digital EEG?

Updated: Oct 09, 2019
  • Author: Eli S Neiman, DO, FACN; Chief Editor: Selim R Benbadis, MD  more...
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As stated in the assessment report of the American Academy of Neurology and the American Clinical Neurophysiology Society, digital electroencephalography (EEG) is an established substitute for recording, reviewing, and storing a paper EEG record. In this sense, digital EEG simply replaces and improves the paper record, much as word processing has improved letter writing over what could be done by hand or even by a typewriter. However, routine digital recording of the clinical EEG does not add new information that was not present in the paper record.

Once the paper recording is made, various options are available for further analysis. Some processing methods, such as different montage displays and digital filtering, simply enhance the visibility of the record. Others, such as calculating the mean band frequencies and different band-energy spectra, may bring into the forefront information that was already there in the paper record but is too tedious and time-consuming to calculate without use of a computer.

Spike recognition is an important enhancement and a great time saver but needs careful review by the interpreting physician. Lately, technologic developments have enabled the authors to record long-term monitoring on small storage devices, making the diagnosis of syncope, seizures, and sleep disorders much easier.

EEG brain mapping visualizes a selected electrical event in the brain and maps its geographic distribution. Attempts have been made to standardize some aspects of brain mapping; however, no clear uniform recommendation has yet emerged. Although frequency bands are fairly well standardized, different ways of calculating the data exist. Normative values are being developed; however, most brain maps are not time locked to an event or brain state; therefore, comparisons of frequency bands are difficult to accomplish across groups or disease states.

A clear definition for the clinical correlation of the brain maps is still needed; therefore, EEG brain mapping and other advanced quantitative EEG (QEEG) techniques should be used only by physicians highly skilled in clinical EEG and only as an adjunct to traditional EEG interpretation.

These tests may be clinically useful only for patients who have been carefully selected on the basis of their clinical presentation. Certain QEEG techniques are considered established as an addition to the digital EEG and include screening for possible epileptic spikes or seizures, long-term EEG monitoring or ambulatory recording, and operating room (OR) and intensive care unit (ICU) monitoring.

Continuous EEG monitoring by frequency trending helps to detect early intracranial processes in the OR or ICU (eg, screening for possible epileptic seizures in high-risk ICU patients). QEEG frequency analysis may be a useful adjunct to interpretation of the routine EEG. In a number of conditions (eg, postconcussion syndrome, head injury, learning disability, attention disorders, schizophrenia, depression, alcoholism, and drug abuse), QEEG remains investigational. On the basis of available clinical and scientific evidence and expert opinions, QEEG is not currently useful in civil or criminal cases.

QEEG is a derivative of regular EEG. The original data must be evaluated before any further mathematical translation of this same data set is done. A thorough understanding and firm knowledge of clinical EEG diagnosis may help prevent erroneous interpretations of digitally displayed mathematical constructs (eg, brain maps and coherence maps).

Ideally, only physicians properly trained in EEG and, in addition, sufficiently well trained in mathematics and computing science should use these new technologies. A substantial risk of erroneous interpretations exists if any of the elements required is missing. Clinical use of any of the EEG brain mapping or other QEEG techniques by practitioners who are not physicians highly skilled and properly trained in clinical EEG interpretation or who have not reviewed the original record should be unacceptable.

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