Special Report: Neuropsychiatry
Electroencephalography (EEG) is
a noninvasive, widely available,
and relatively inexpensive test
that can help exclude or identify structural
or functional factors contributing
to psychiatric syndromes. This article
defines the clinical usefulness of EEG
in evaluating neuropsychiatric disorders,
emphasizing the complementary
nature of the visually inspected standard
EEG (SEEG) and the computeranalyzed
quantified EEG (QEEG).
The recent evolution of neuropsychiatry/behavioral neurology as a
subspecialty linking these formerly
disparate fields represents a paradigmatic
shift regarding the responsibility
of psychiatrists in diagnosing and
managing behavioral disorders with
concomitant and demonstrable brain
pathology such as dementia or head
injury. In addition, the biologic underpinnings
of many mental illnesses,
including bipolar disorder and depression,
are now described in terms of their
anatomy and physiology. QEEG analysis increases the sensitivity of EEG to
physiologic or pathologic changes associated
with such disorders.
SEEG refers to the visual analysis of
ongoing voltage recordings from multiple
scalp locations. Two types of EEG
deviations are usually indicative of
significant cerebral pathology. The first
is paroxysmal activity, including sharp
waves, spikes, and episodic slow
waves, indicating episodic abnormal
neuronal discharges. These can be
focal, suggesting structural pathology,
or bilateral and more suggestive of
functional pathology. The second type
of EEG deviation is sustained slowing
of normal brain rhythms. Slowing also
can be diffuse, indicating more generalized
pathology, or focal, indicating
a localized pathology.
The most frequent reason for an EEG
referral is to exclude a general medical
condition, such as delirium, or a specific
neurologic problem, such as epilepsy,
as a cause of or a contributing factor to
the presenting symptoms. Since the use
of routine test batteries to exclude medical conditions is costly,
clinicians must rely primarily
on 2 red flags to trigger organic
workups: unusual presentations
and atypical age at onset. The
yield is consistently low when
using neuroevaluative tests to
uncover causes such as tumors
or aneurysms for syndromes
presenting without manifest
neurologic disturbances. It is
much more likely that an EEG
will uncover a factor that may
be contributing to, but does not
necessarily fully explain, the
syndrome. It may also be helpful
in revealing a factor that
could help guide treatment,
such as temporal lobe spiking in panic
After the EEG has been recorded and
visually interpreted by the electroencephalographer,
it may be analyzed
further using quantitative means.2
QEEG analysis is always a post hoc
procedure done after visual interpretation
of the SEEG by a qualified electroencephalographer. It is specifically
not recommended for use clinically as
a stand-alone procedure. At its most
basic level, QEEG provides a method
of calling the electroencephalographer's
attention to aspects of the original EEG
record that may have been overlooked.
QEEG's quantitative nature makes it
exquisitely sensitive to subtle frequency
changes and to abnormalities in the coherence of activity within and among
Brain activity varies among healthy
people, and normal variability must be
distinguished from that outside the normal
range. An underlying assumption is that
the more unusual the patient's brain activity
compared with that of normal persons,
the more likely it is that the statistical
abnormality represents pathology. The
establishment of normal limits is greatly
aided by quantitative analysis comparing
the patient's QEEG with those derived
from large groups of healthy persons.
Brain activity also changes with age, and
QEEG tracks the moving window of normal
limits across the entire life span.
In addition, QEEG can help the physician
arrive at a specific diagnosis.
Patients who have known neuropsychiatric
disorders often show characteristic
QEEG profiles, distinguishing them
from patients who have similar disorders.
When facing a difficult diagnostic
question, the physician can compare
the patient's QEEG with the profiles
characteristic of the different diagnostic
possibilities, looking for the best fit.
An extensive body of research shows
that the accuracy of such computerized
diagnostic classifications on the basis
of QEEG alone typically exceeds 80%,
although in an actual clinical setting the
physician always makes the diagnosis,
informed by other sources of information
in addition to QEEG. Well-replicated
studies have demonstrated QEEG
classification accuracies high enough to
be useful in diagnosing learning and
attention disorders in children, and mood
disorders (including bipolar disorder)
and dementia among adults.3
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