Electroencephalogram (EEG)
- Useful
tool in epilepsy/seizure diagnosis, metabolic encephalopathy, diagnosis in
herpes encephalitis.
- May be
used as confirmatory test in brain death.
- Alpha – 8-13 Hz, symmetric, present
posteriorly (occipital) with eyes closed, disappear (are blocked) with eye
opening
- Beta – above 13 Hz; symmetric,
present frontally; no effect with eye opening
- Gamma (4-8 Hz) and Delta
(less than 4 Hz) – seen in children and young adults with frontal and
temporal predominance
- Theta waves – 4-7 Hz
- Parietal
and temporal areas in children
- Delta waves – 1-3 Hz
- Spike
or sharp waves:
Fast, higher voltage waveforms which, when paroxysmal, are suggestive of
epilepsy
- EEG in
Sleep
- Stage I
– loss of alpha waves
- Stage II
– sleep spindles, K-complexes
- Stage
III – delta waves, some spindles
- Stage IV
– Delta waves only.
- Sleepwalking,
night terrors
- REM –
beta waves
- Alpha
rhythm
- posteriorly-dominant
rhythm (PDR)
- most
prominent in the occipital leads
- best seen
when the patient is awake with eyes closed
- attenuates
eye opening/movement and drowsiness
- Amplitude
– 20-70 microvolts; L-R differences should be less than 50%
- Slowing –
reflects white matter more than cortex
- Diffuse
slowing – encephalopathy NOS (90% are metabolic)
- Focal
slowing – usually a structural lesion; the more acute the lesion, the
more prominent the asymmetry
- Spikes
(20-80 msec) and Sharps (80-200 msec)
- have
steeper upslope than downslope
- followed
by a slow wave (usually delta or theta)
- show up as
a 'phase reversal' on the EEG record
- vertex
sharp waves (stage I sleep) and spindles/K-complexes (stage 2 sleep) are
normal
- Patterns
- Febrile
seizures – 6
month-3 years old
- last
<15 minutes
- EEG
normal or photosensitive
- 1% get
epilepsy unless seizures are complex
- Infantile
spasms – 3-7
months old
- flexion
(jack-knife or salaam) movements
- hypsarrythmia
on EEG
- treat
with ACTH (controversial)
- Absence
seizures – 4-8
years old
- 3 Hz
spike-and-wave on EEG
- induced
by hyperventilation
- treat
with ethosuxamide
- Rolandic
Epilepsy (BECHTS) – childhood or adolescent
- includes
vocalizations
- sometimes
has generalized tonic-clonic seizures on awakening
- spontaneously
resolves
- CJD
- rapidly
progressive dementia with myoclonus (especially with startle)
- evolving
EEG with background disruptions then PLEDS then quiet