Electroencephalogram
Electroencephalograms or EEGs are a
basic screening measure of brain waves which is performed
in neuropsychiatry both to detect abnormal firing
in the brain and to find local (focal) abnormalities.
Both sleep and wake EEGs with activating procedures
such as hyperventilation and photic stimulation are
useful as each can give valuable information and demonstrate
abnormalities. Hyperventilation - overbreathing -
which changes the proportion of carbon dioxide in
the body and therefore the acidity / alkalinity level
should be performed only in the absence of medical
conditions contra-indicating it. EEGs appear reasonable
in neuropsychiatric evaluations when there are seizure
history possibilities or possible temporolimbic features
(as reflected on the INSET), or with the episodic
nature of symptoms or a history of atypical spells
. Sleep records have been well demonstrated to more
likely find focal pathology than waking EEGs which
is why they are generally routinely performed now.
However waking EEGs have also have a high pick up
rate and sleep EEGs cannot be interpreted without
the wake EEG justifying a wake record.
Prior to the development of the EEG,
by the neuropsychiatrist, Hans Berger in the 1930's,
all seizure disorders were classified with mental
disorders. EEG technology still remains rather primitive
and reflections of brain waves from the perspective
of analysis of psychopathology somewhat limited. Nevertheless,
the only definitive way of demonstrating that a symptom
or physical sign such as, for example, an olfactory
hallucination is definitely epileptic, is the demonstration
while the person is having that experience of correlates
of seizure phenomena on EEG, such as spike-wave paroxysms
- episodes of half to several seconds of usually sharp
abnormal brain waves, sometimes localized in the brain
e.g. in the right temporal lobe. This demonstration
is unusual unless the seizure phenomena are relatively
uncontrolled, as an EEG is just a short cross-sectional
measure for an hour or two of a patient's life-cycle.
Even in the event of the patient having an experience
which may be a seizure, the EEG correlate may not
necessarily be of a spike wave kind but depending
on location, it could be normal or show a marked slowing,
with a non-specific theta rhythm generally of limited
help unless focal or a delta rhythm, which is frankly
abnormal unless the patient is asleep (theta is 4
to 7 cycles per second, delta is less than 4). It
is occasionally extremely difficult to localize such
features on scalp EEG even when firing is occurring
because symptoms may occur from the mesial temporal
or deep structures within the brain which do not easily
manifest on surface EEGs.
Routine Electroencephalograms (EEGs)
involve both waking records with special activating
procedures such as hyperventilation and photic stimulation
(in the absence of medical conditions contra-indicating
these) as well as sleep records. EEGs should be ordered
not only in possible seizure disorder , but appears
reasonable given any possible temporolimbic features,
episodic nature of symptoms or history of atypical
spells. Sleep records may increase the potential delineation
of focal abnormality such as a temporal lobe focus
by approximately fourfold than waking EEGs. However
waking EEGs have a high pick up rate and sleep EEGs
cannot be interpreted without the wake EEG so both
should be performed. A normal EEG does not imply absence
of epilepsy.
EEGs are possibly under-used in psychiatry
partly because electroencephalographers have a broader
range of what constitutes normality searching mainly
for focal and seizure phenomena. They are generally
not psychiatrists and potentially valuable research
and clinical information may be lost. For example,
testable hypotheses are that relatively flat EEG tracings
may be more common in certain personality disorders,
with certain psychotropics, or in a subpopulation
of schizophrenia. Seldom is this kind of background
even reported on.
The administration of chloral hydrate
(e.g. 1 gram as premedication) prior to the sleep
record is useful as this induces sleep with little
changes of significance in the electroencephalogram
and does not prevent the demonstration of focal abnormalities.
Certain medications should be particularly avoided
in EEGs. The benzodiazepine group are the worst offenders
as by virtue of their very strong anti-epileptic effects,
they have profound effects in normalizing the EEG.
Such effects at a receptor level may last weeks even
with the apparent short acting benzodiazepines so
that the yield of demonstrating epilepsy after the
patient has had benzodiazepines administered apparently
decreases substantially, although adequate data in
this regard is not easily available.
Special electrode placements
may increase yield by a few percent, but are seldom
used today: With nasopharyngeal electrodes,
the greater yield was insubstantial; and sphenoidal
electrodes placement, unfortunately, requires time
and expertise and cause discomfort limiting their
use. A recent suggestion which I recommend has been
the placement of electrodes on the buccal skin surface
in the area of the submandibular notch - possibly
as effective in picking up foci as sphenoidal placements.
Specialized centers use cerebral cortical or submeningeal
strip placements during neurosurgery procedures
and these may show firing, for example, in patients
with temporal lobe epilepsy and psychosis, in the
region of the hippocampus. The direct placement of
intracranial electrodes shows how commonly spike firing
may be occurring in this area with no correlate of
any kind on surface EEGs.
Developments in this regard have been
rapid over the past few years. EEG Telemetry
involves prolonged monitoring over periods of time
varying from 12 hours to 2 weeks while the patient
is generally confined to a particular room. Cable
telemetry is most commonly used. This involves,
for example, a 25 foot cable connected to the EEG
montage on the patient's head. Very often no seizure
manifestations are picked up for prolonged periods
of time because seizures only occur paroxysmally.
Moreover, those patients evaluated in a specialized
center with EEG telemetry are invariably so atypical
that the hypothesized seizure originates deep within
the brain. The apparatus is very expensive and the
costs involved in monitoring patients are thousands
per day at times for two weeks. Instead, home ambulatory
electroencephalograms are easily available and should
in psychiatry become the state of the art.
Ambulatory Electroencephalogram
Home Ambulatory Electroencephalograms
(EEG) with the patient not modifying medication is
a valuable test as the patient's symptomatology can
be monitored day and night in a natural environment
of home using computerized filtering of artefact.
The advantage of this technique is to establish if
any scalp electrode can detect events such as atypical
spells alerted to by pushbuttons which could be reflecting
deep brain electrical activity . It has limited availability
at this point, however, but our pick up rate for atypical
spells (paroxysmal neurobehavioral disorder) and seizures
is very high - a major advance over routine electroencephalography.
Recent advances in EEG technology may
ultimately change the whole perspective in its use
in psychiatry. Computerized EEG monitoring
allows breakdown of wave forms and allows correlation
with evoked potentials including cognitive evoked
potentials. It also facilitates demonstrations of
changes in particular areas of the brain which can
be easily delineated at a visual level. This should
prove to be a useful psychophysiological correlate
of psychopathology. Indeed, this may be the beginning
of an important new era. However, at this point in
time it is still experimental.
Ambulatory Electroencephalogram (EEG)
with the patient not modifying medication is a valuable
test given episodic symptomatology which can be monitored
day and night in a natural environment of home using
computerized filtering of artefact. One advantage
of this technique here is to establish if any scalp
electrode can detect events such as atypical spells
alerted to by pushbuttons reflecting deep brain electrical
activity.