By Nash N. Boutros, MD
The Electroencephalogram in the Management of Psychiatric Conditions
The electroencephalogram (EEG) has a limited but definitive role in understanding and managing psychiatric conditions. When the presentation is unusual, a neurological workup that includes an EEG is essential. In conditions in which EEG abnormalities are demonstrably common, an EEG should be considered part of the essential workup. A simplified EEG can have substantial diagnostic usefulness, particularly in emergency department settings. The abbreviated EEG can be done in a matter of minutes using a 10- or 12-channel recording instrument.
The EEG as a diagnostic tool
The EEG is an extremely sensitive voltmeter. Typical signals range from approximately 30 to 80 μV, but can be as low as 10 μV in some tracings or as high as 150 or 200 μV in some high-voltage “spike” epileptic discharges. Electrical potentials measured between any 2 EEG electrodes fluctuate or oscillate rapidly, usually many times per second. These EEG signals are the result of summated field potentials generated by excitatory and inhibitory postsynaptic potentials in vertically oriented pyramidal cells of the cortex.
The simultaneous recording of brain waves from many scalp locations is important because it:
• Allows direct comparisons between homologous cortical regions
• Permits recording arrays to locate focal or regional abnormal features more clearly
• Increases the ability to detect various artifacts (ie, waveforms of non-brain origin) that can contaminate the recording
The EEG of an awake and relaxed healthy adult is usually dominated by frequencies between 8 and 13 cycles/second (8 to 13 Hz alpha activity). Once the person focuses his or her attention or becomes stressed, the frequency increases to the beta range (above 13 Hz). When an adult begins to get drowsy, EEG rhythms slow to the theta (4 to 8 Hz) range and finally to the delta (below 4 Hz) range with sleep. The appearance of excessive theta or any delta during wakefulness is a definite abnormality. While excessive beta during wakefulness has been linked with anxiety disorders, it is not considered an EEG abnormality (by today’s standards) and cannot be used to diagnose anxiety states.
The prevalence of EEG abnormalities in psychiatric patients is significantly elevated and ranges from 20% to 68% higher than in healthy controls.1-4 EEG findings in psychiatric populations include generalized or focal slowing of cortical activity and a variety of focal or generalized paroxysmal EEG discharges. Part of the reason that these patients have such a wide range of EEG abnormalities may be because the EEG signal is quite sensitive to many variables (eg, metabolic, vascular, endocrinological) that affect CNS function.
Although EEG abnormalities may not have direct primary psychiatric diagnostic specificity, they suggest the presence of other, organic/medical/physiological variables that could contribute to the psychiatric presentation. Moreover, EEG discharges without overt seizures (ie, isolated epileptic discharges) may have behavioral consequences such as emotional lability, irritability, or temper dyscontrol that cut across broad diagnostic labels.5,6
Indications for clinical EEGs in patients with psychiatric disorders
The EEG may reveal 1 of 2 classes of deviations: the slowing of normal rhythms and the appearance of abnormal paroxysmal (episodic) electrical activity suggestive of an epileptic process. Both kinds of abnormalities can be focal and suggestive of a localized pathological process, or generalized and more diffused, suggestive of a degenerative or metabolic process. If slowing is suspected, the patient must be awake while the EEG is recorded; if paroxysmal activity is suspected, the EEG needs to be done during both sleep and wake periods. The Table summarizes indications for which EEGs might prove useful for patients with psychiatric disorders.