A low-voltage electroencephalogram is a record in which the amplitude of cerebral activity is below 20 microvolts globally.
It occurs in 10% of normal adults and in 3% of normal adolescents.
It is found particularly often in states of anxiety, after minor head injuries, cerebrovascular disease, postencephalitic states, Parkinsonism, after subarachnoid haemorrhage, Huntington’s chorea, Pick’s disease, hypoglycemia, hypothyroidism. A low-voltage recording occurs very rarely in epilepsies but is possible.
The most frequent causes are chronic anxiety or drowsiness, thickness of extracerebral tissues, and possibly genetic factors.
It is important to determine whether the low amplitude is caused by chronic anxiety, drowsiness, or if the low amplitude represents a lesion of the structures responsible for generating electrocerebral activity.
In states of anxiety found in patients with psychiatric problems, chronic headaches of different origins, and syncopal attacks during resting recording, there may be an increased amount of low-voltage fast activity.
Where chronic drowsiness is the problem, such as may occur in postencephalitic states, postconcussional brain syndromes, and disturbances of sleep rhythms, a small amount of low amplitude theta activity may be seen.
Activating procedures can lead to voltage enhancement:
- Hyperventilation
- Photic Stimulation
- Sleep
- Short latency anxiety meds (ex. diazepam)
- Central stimulating drugs (ex. phenyl-methyltetrahydroxazin orally or betaethylbetamethylglutarimide-i.v.)
If it does not change during activating procedures and remains the same during sleep, it should be considered as abnormal as it represents a lesion involving structures generating electrocerebral activity.
When it occurs focally, it may be due to scalp edema.
Suppression is the term used to describe the amplitude of cerebral activity below 10 microvolts globally.
Synek, V. M. (1983). The low-voltage electroencephalogram. Clinical Electroencephalography, 14(2), 102-105.
