Non-Epileptiform Patterns

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Non-Epileptiform Patterns

• Dr Lim Shih Hui
• Senior Consultant Neurologist
• Singapore General Hospital

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EEG Interpretation

• Normal
• Lack of Abnormality
• Abnormal
• Non-epileptiform Patterns
• Epileptiform Patterns

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Non-Epileptiform Patterns

• Special Patterns
• Excessive fast
• Asymmetry
• Periodic pattern
• Triphasic waves
• Periodic lateralized epileptiform discharges
  (PLEDs)
• Burst suppression
• Background suppression
• Sleep-onset rapid eye movement

• Slow Activity
• Background slow
• Intermittent slow
• Continuous slow
• Special Patterns Used Only In Stupor Coma
• Alpha coma
• Spindle coma
• Beta coma
• Theta coma
• Delta coma

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Background Slow
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Slow Waves

• Indicates underlying cortical dysfunction,
  ?deafferentation of the cortex
• Location indicates a focal, lateralized or
  generalized cortical dysfunction
• Degree, persistence and reactivity roughly
  correlate with severity of dysfunction
• Rhythmic slowing more likely to be
  electro-physiological disturbances
• Polymorphic slowing more likely to have
  structural abnormality

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Background Slow Activity

• Frequency of the background rhythm is lower than
  normal value for the age.
• 1 yr lt5 Hz
• 4 yr lt6 Hz
• 5 yr lt7 Hz
• gt8yr lt8 Hz
• Must be verified that slowing is not due to
  drowsiness

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Background Slow ActivityInterpretation

• Cortical or subcortical mechanism involved in the
  generation of the background rhythm are disturbed
  ? synchronization of background rhythms of
  abnormally slow frequency
• A manifestation of a diffuse dysfunction of the
  cortex, or subcortical gray structures
• A non-specific EEG finding that have different
  causes
• Adult usually disorders of cerebral perfusion
  metabolic and toxic cause
• Childhood perinatal sequelae

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Intermittent Slow, Generalized
Intermittent Slow, Generalized
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Intermittent Slow Activity

• Occurs intermittently and is not caused by
  drowsiness
• Rhythmic or irregular
• Generalized, regional or lateralized
• Background rhythm is generally well preserved
  indicating that cortical and subcortical
  mechanism involved in its generation are
  functionally normal
• A non-specific functional cerebral dysfunction
• Has diverse cause
• Can be an early manifestation of continuous slow
  activity or epileptiform changes

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Generalized Intermittent Slow Activity

• Can be caused by infra-tentorial or
  supra-tentorial lesions
• Unprovoked intermittent slow
• diffuse cortical dysfunction
• generalized epilepsy
• Adult predominantly frontal (Frontal
  Intermittent Rhythmic Delta Activity FIRDA)
• Children predominantly occipital (OIRDA)

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Intermittent Rhythmic Slow, Generalized (FIRDA)
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Intermittent Rhythmic Slow, Regional,
Bi-occipital (OIRDA)
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Intermittent Rhythmic Slow (IRS)

• More specific subclass of intermittent slow
• Appeared grouped in bursts
• Relatively rhythmic
• Generalized IRS
• Diffuse involvement of cortical and subcortical
  grey structures (e.g. diffuse encephalopathy or
  generalized non-focal epilepsy)
• Mesial cortical lesion
• Focal subcortical grey matter lesion infra- or
  supra-tentorial destructive process e.g. tumors
  or raised intracranial pressure

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Continuous Slow, Generalized
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Continuous Slow Activity

• Occurs continuously
• Irregular (polymorphic)
• Lies within frequency range of delta/theta waves
• Non-responsive to external stimuli
• Clearly exceeds the amount considered
  physiologically normal for the patients age
• Severe disturbances of interneuronal connections
  or of the biochemical environment of cortical
  neurons ? continuous slow activity

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Continuous Slow, Lateralized, Left Hemisphere
Continuous Slow, Lateralized, Left Hemisphere
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Alpha Coma

• Predominant alpha activity in a patient with a
  clinical state of coma
• Due to
• Discrete lesion of the ponto-mesencephalic level
• Severe anoxic encephalopathies
• Drug intoxication

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Alpha Coma
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Theta Coma

• Predominant theta activity in patient in coma
• Due to severe diffuse encephalopathy
• Potentially reversible prognosis depends on
  underlying condition

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Theta Coma
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Other Coma Patterns

• Spindle Coma
• Due to lesion at high mesencephaic level
• If not due to progressive lesion ? good prognosis
• Beta Coma
• Most frequently due to drug intoxication
  potentially reversible
• Delta Coma
• Severe diffuse encephalopathy
• Reversibility depends on underlying condition

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Sleep Coma
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Excessive Fast

• Beta activity of gt 50 uV
• Present during at least 50 of awake recording
• Frequently due to sedative medication

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Excessive Beta Activity
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Asymmetry

• Asymmetries of amplitude of background rhythms
• Asymmetries of frequency are included under focal
  slow
• Asymmetries are considered significant when
  amplitude in one hemisphere with the lower
  amplitude is lt50
• A reliable sign of focal structural lesions on
  the side that has lower amplitude
• e.g. Porencephalic cyst, subdural hematoma

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Asymmetry, Decreased Background, left
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Periodic Pattern

• Relatively stereotyped waveforms
• Frequently sharp waves
• Appear in a periodic or quasiperiodic fashion
• Generalized
• Indicative of an acute or sub-acute, severe and
  diffuse encephalopathy
• Repetition rate
• 1-2 every 1-2 seconds CJD, post-hypoxic
• 1 every gt 4 seconds SSPE

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Periodic Pattern, Generalized (CJD)
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Periodic Pattern, Generalized
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Periodic Pattern, Generalized (Post-Hypoxic)
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Triphasic Waves

• High voltage (gt70 uV)
• Triphasic, predominantly postive
• Generalized, maximum anterior
• Tend to be periodic, 1-2 Hz
• Due to metabolic encephalopathy (e.g hepatic
  encephalopathy) or any condition that produce
  intermittent
• Usually associated with alteration of
  consiousness but not as severe as stupor or coma

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Triphasic Waves
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Periodic Lateralized Epileptiform Discharges
(PLEDs)

• Sharp transients including sharp wave or spikes
• Appear in a periodic or semi-periodic fasion
• Lateralized or focal
• Seen in
• Acute or subacute, severe, focal destructive
  lesions (e.g CVA, fast growing tumors)
• Focal epileptogenic lesion not necessary
  associated with can acute or subacute underlying
  structural pathology

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PLEDs, Regional, Left Posterior
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PLEDs, Regional, Left Frontal
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Burst Suppression

• A subgroup of periodic patterns in which activity
  between complexes is suppressed
• Generalized
• Seen in extremely severe toxic or anoxic
  encephalopathy may precede electrocerebral
  inactivity
• Patients always in stupor or coma

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Burst-Suppression
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Burst-Suppression
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Burst-Suppression
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Sleep-Onset-REM-Period
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Sleep Onset Rapid Eye Movement

• Occurrence of REM sleep lt15 min after falling
  asleep
• Dysfunction of subcortical mechanism that induce
  sleep
• Occur in
• Narcolepsy
• Severe sleep deprivation with consequent REM
  rebound
• Withdrawal of MAO inhibitors or TAD
• Neonates ? normal