Recognition of abnormal EEG.
- 1. Recognition of abnormal EEG SHEHZAD HUSSAIN 02-FEB-2017
- 2. Contents 1. Introduction 2. The criteria for being normal or abnormal 3. Factors that affect EEG 4. Frequency 5. Morphology 6. Epileptiform abnormalities 7. Non Epileptiform abnormalities
- 3. Introduction Electroencephalograph represents complex irregular signals that may provide information about underlying neural activities in the brain. Since the human brain generates a small yet measurable amount electrical signal the degree of activity is measurable. The brain waves recorded from the scalp have a very small amplitude of approximately within 100µV. The frequencies of these brain waves range from 0.5 to 100 Hz, and their characteristics are highly dependent on the degree of activity of the brain’s cerebral cortex.
- 4. Cont.… The data generated has proven to be particularly useful for the following purposes: 1) to confirm a clinical suspicion of epilepsy; 2) to identify Epileptiform activity; 3) to document seizures that the patient is unaware of; 4) to evaluate response to therapy; 5) to evaluate nocturnal or sleep-related events; 6) to evaluate suspected pseudo seizures and 7) to evaluate syncope.
- 5. Factors that affect EEG • The following factors are the most important for interpretation of an EEG. I. Age II. State III. Medication IV. Technical factors V. Standard setting of machines (filter setting LFF, HFF, sensitivity etc) VI. Temperature (specially in low tem <27ċ)
- 6. Frequency An electroencephalograph (EEG) represents complex irregular signals that may provide information about underlying neural activities in the brain. Information about waveform frequency and shape is combined with the age of the patient, state of alertness or sleep, and location on the scalp to determine significance. Normal EEG waveforms, like many kinds of waveforms, are defined and described by their frequency, amplitude, and location. For a normal human being, brain waves can be categorized as one of the four wave groups.
- 8. Cont.. The spectra of these waves are: 1. The Delta waves which include all the waves in the EEG below 3.5 Hz. They occur in deep sleep, in childhood, and in serious organic brain disease. 2. The Theta waves have frequencies between 3.5 and 7.5 Hz. These occur mainly during the childhood, but they also occur during emotional stress in some adults.
- 9. Cont.. 3. The Alpha waves are rhythmic waves occurring at a frequency range between 8 and 13.5 Hz, which are found in all normal persons when they are awake in a quiet, resting state of cerebration. The Beta waves are very low amplitude, and high frequency range between 14 and 30 Hz. They are affected by mental activity.
- 10. Morphology: • By means of morphology we identify the normal waveforms, including K complex, V waves, lambda waves, positive occipital sharp transients of sleep (POSTS), spindles, mu rhythm, spikes, sharp waves, and certain delta waves (polyphasic and monophasic shapes). • These waves are recognized by their shape and form and secondarily by their frequency. They include waves that may be normal in some settings and abnormal in others (eg, spikes, sharp waves).
- 12. Slow waves
- 13. Steps in the analysis of suspected abnormal transients; • Is the transient cerebral or artifactual? • If cerebral, is it normal or abnormal? • If abnormal, is it specific for epilepsy (epileptiform)? • If epileptiform, is it focal (or regional, or lateralized) or generalized? • If focal or regional, what is the field of the discharge? Discharges Associated with Epilepsy • Interictal Epileptiform Discharges • Seizure Patterns or Ictal Patterns
- 14. Cont.. • Criteria for epileptiform discharges • VOLTAGE: high – MORPHOLOGY: shorter, lower amplitude first phase – longer, higher amplitude second phase – polyphasic – aftergoing slow wave – different from background • Polarity: great majority are predominantly surface negative
- 17. Cont.. • DURATION: short (but not too short) • Spike: <70 msec • Sharp wave: 70-200 msec • BACKGROUND: abnormal • Must have a physiologic field • LOCATION & STATE: unlike normal physiologic transients Epileptiform Discharges • Spikes (20-70 msec) • Sharp waves (70-200 msec) • Spike-and-wave, Slow-spike-and-wave, Sharp-and-slow-wave, Multiple spike (Polyspike), Multiple-spike-and-slow-wave (Polyspike-and-slow- wave) Complexes
- 18. A- spike; B- sharp wave; C- spike-and-wave complexes; D- sharp-and-slow-wave complexes; E- slow-spike-and-slow-wave complex; F- polyspike-and-wave complex; G- multiple-sharp-and- slow- wave complex; H- polyspike complex; I&J- multiple sharp wave complexes. Even though spikes and sharp waves usually have after-going slow waves, the term spike-and-wave complex is usually reserved for the situation where the slow wave is very prominent, higher in voltage than the spike.
- 19. Ictal vs interictal discharges • Ictal discharge usually not a repetition of interictal discharges, except in generalized absence seizures • Occasional patterns can be either ictal or interictal (spike-and- wave discharges, paroxysmal fast activity)
- 20. The non-epileptiform EEG abnormalities in the context of the neurological disorders; • When the non-epileptiform abnormalities are seen on an EEG record, they are not specific for an underlying etiology. In these situations, however, the EEG provides evidence of organic electrophysiological dysfunction and the patterns observed may orientate for the diagnostic possibilities. The most important types of the non-epileptiform EEG abnormalities are Focal slow activity - Focal slow activity may be an indicative sign of focal cerebral dysfunction, especially in awake adults, and it seems to be the result of a cortex deafferentation (the interruption or destruction of the afferent connections of nerve cells) from subcortical structures.
- 21. Cont… • It was first described by Walter, in 1936, who proposed the term "delta waves" for focal slow activity associated with tumors involving cerebral hemispheres. • It is the most common phenomenon encountered in clinical EEG that is indicative of a localized structural lesion. • some cases, focal slow activity may presents as focal and irregular slow activity in the delta frequency, receiving the designation of polymorphic delta activity (PDA). which is usually due to a structural lesion or a subcortical dysfunction (although the anatomic correlation is not always exact)
- 22. EEG in Epilepsy Summary; • The EEG remains the most sensitive and specific test in support of epilepsy • There is great potential for over-reading epileptic abnormalities on EEG • More damage is done by over-reading than under-reading • The EEG should never be a substitute for a detailed clinical history.
- 23. The End Do not disappoint the one whose hope lies in you. Hazrat Ali A.S