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Non-Epileptiform Patterns

Non-Epileptiform Patterns. Dr Lim Shih Hui Senior Consultant Neurologist Singapore General Hospital. EEG Interpretation. Normal Lack of Abnormality Abnormal Non-epileptiform Patterns Epileptiform Patterns. Slow Activity Background slow Intermittent slow Continuous slow

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Non-Epileptiform Patterns

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  1. Non-Epileptiform Patterns Dr Lim Shih Hui Senior Consultant Neurologist Singapore General Hospital

  2. EEG Interpretation • Normal • Lack of Abnormality • Abnormal • Non-epileptiform Patterns • Epileptiform Patterns

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

  4. Background Slow

  5. 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

  6. Background Slow Activity • Frequency of the background rhythm is lower than normal value for the age. • 1 yr: <5 Hz • 4 yr: <6 Hz • 5 yr: <7 Hz • >8yr: <8 Hz • Must be verified that slowing is not due to drowsiness

  7. 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

  8. Intermittent Slow, Generalized Intermittent Slow, Generalized

  9. 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

  10. 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)

  11. Intermittent Rhythmic Slow, Generalized (FIRDA)

  12. Intermittent Rhythmic Slow, Regional, Bi-occipital (OIRDA)

  13. 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

  14. Continuous Slow, Generalized

  15. 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 patient’s age • Severe disturbances of interneuronal connections or of the biochemical environment of cortical neurons  continuous slow activity

  16. Continuous Slow, Lateralized, Left Hemisphere Continuous Slow, Lateralized, Left Hemisphere

  17. 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

  18. Alpha Coma

  19. Theta Coma • Predominant theta activity in patient in coma • Due to severe diffuse encephalopathy • Potentially reversible; prognosis depends on underlying condition

  20. Theta Coma

  21. 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

  22. Sleep Coma

  23. Excessive Fast • Beta activity of > 50 uV • Present during at least 50% of awake recording • Frequently due to sedative medication

  24. Excessive Beta Activity

  25. 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 <50% • A reliable sign of focal structural lesions on the side that has lower amplitude • e.g. Porencephalic cyst, subdural hematoma

  26. Asymmetry, Decreased Background, left

  27. 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 > 4 seconds: SSPE

  28. Periodic Pattern, Generalized (CJD)

  29. Periodic Pattern, Generalized

  30. Periodic Pattern, Generalized (Post-Hypoxic)

  31. Triphasic Waves • High voltage (>70 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

  32. Triphasic Waves

  33. 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

  34. PLEDs, Regional, Left Posterior

  35. PLEDs, Regional, Left Frontal

  36. 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

  37. Burst-Suppression

  38. Burst-Suppression

  39. Burst-Suppression

  40. Sleep-Onset-REM-Period

  41. Sleep Onset Rapid Eye Movement • Occurrence of REM sleep <15 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

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