“Normal” routine EEGs are not always normal



Robert Thatcher (Neuro-scientific research)

Routine EEG’s do not always show brain damage although we know that a person might have suffered brain injury after trauma. We refer to EEG investigations with high expectancy and often the EEG shows no abnormality.

The severity of traumatic brain injury in patients is normally judged by emergency hospital admission records, the Glasgow Coma Scale (GCS) and duration of coma and amnesia. The accurate measuring of the GCS may be in doubt, where as the present EEG severity index may facilitate accurate diagnosis of the extent of brain injury by providing an objective and independent measure of the severity of Traumatic Brain Injury (TBI).

There are often reports of headaches, fatigue, impaired memory, reduced concentration and attention, reduced information processing capacity, depression, aggression, anxiety, irritability, sleep disturbances, sexual dysfunction, posttraumatic personality changes, temper outbursts, self centered behaviour, emotional lability and reduced social awareness which are thought to be associated with frontal and temporal lobe damage. The presence thereof can be measured by psychometric assessment but the severity level of the brain damage is still unclear.

Although the Glasgow Coma Scale, the duration of loss of consciousness and duration of posttraumatic amnesia, are valuable clinical predictors of the severity of TBI, there are limitations. The GCS is often not measured in emergency rooms. The duration of loss of consciousness and posttraumatic amnesia is often only a prediction and not necessarily correct.

The routine EEG and MRI are also not sensitive enough to predict the severity level or difference between mild, moderate or severe level of TBI.

A study done by Dr Robert Thatcher had the purpose of developing an objective and quantitative metric of the severity of brain injury by using EEG obtained in the long term post-acute period from 15 days to 4 years post injury. For the purpose of this article, the method of study will not be discussed. (The Journal of Neuropsychiatry and Clinical Neurosciences 2001;13:77-87)

There were significant correlations between emergency admission measures, EEG discriminant scores and 7 neuropsychological tests: Wechsler Adult Individual Scale Revised, Boston Naming Test, Word Fluency Test, Attention Tests, Wisconsin Card Sorting Test, Wechsler Memory Scale revised and California Verbal Learning Test. (Robert Thatcher et al)

The results of Thatcher’s research indicate that TBI has a long lasting effect on cognitive functioning and that the Q EEG provides a measure of persistent neurological reorganization resulting from the injury.

Patients who present with persistent cognitive and neuro-phychological deficits many months after the injury, do not have access to accurate estimates of the severity of the TBI. The EEG severity index may facilitate accurate diagnoses of the extent of brain injury and provides an objective and independent measure of the severity of TBI. (The Journal of Neuropsychiatry: Patients included in the research: From the Bay Pines Veterans Affairs Medical Center, Bay Pines, Florida and Defense and Veterans Head Injury Program, Washington DC. By Dr R Thatcher).

The TBI Severity Index is an estimate of the neurological severity of injury and should be viewed as an adjunct to the evaluation of the patient. It does not serve as a primary basis for diagnosis.

How do we derive a TBI Severity Index?

STEP 1: Routine EEG

Routine EEG recordings are performed to measure brainwaves and the most prominent purpose of performing EEG’s is to diagnose epilepsy and brain damage. These recordings do not always offer enough information.

STEP 2: Quantitative EEG
The Q EEG can be compared to observing light through a prism. Detail is accentuated which cannot be seen with the naked eye on a routine EEG recording. The Q EEG provides information regarding brain functioning and cognition as compared to a normative or reference database (Thatcher Neuro-Guide). We get information from the Q EEG regarding absolute and relative power, ratio of different frequencies in the brain, coherence or connectivity of the brain, phase lag scores and asymmetry scores.

STEP 3: Derive discriminant scores by importing into NeuroGuide (Dr R Thatcher)

Discriminant scores were accomplished through mathematical procedures described by Thatcher et al.

So a “normal” EEG might be an abnormal Q EEG.

For more information:
Dr. Annemie Peché

0823356133 / 011 6756138