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Electroencephalogram as a neurological test especially in epilepsy


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PRINCIPLE An electroencephalogram (EEG) is a test to measure the electrical activity of the brain. EEG refers to the recording of the brain's spontaneous electrical activity over a short period of time, usually 20–40 minutes, as recorded from multiple  electrodes  placed on the  scalp .  Your brain cells communicate via electrical impulses and are active all the time, even when you're asleep. This activity shows up as wavy lines on an EEG recording.


INDICATIONS An EEG can determine changes in brain activity that may be useful in diagnosing brain disorders, especially epilepsy. Brain tumor Head injury Brain dysfunction that may have a variety of causes (encephalopathy) Inflammation of the brain (encephalitis) Stroke Sleep disorders Memory impairment It may be used to confirm brain death in someone in a persistent coma.


CONTRAINDICATIONS Photic stimulation and hyperventilation The patient performs 3 minutes of hyperventilation when there are none of the following contraindications: cardiac disease respiratory disease sickle cell disease severe hypertension acute stroke


NORMAL EEG Brain electrical activity has certain frequencies (the number of waves per second) that are normal for different levels of consciousness. For example, brain waves are faster when you are awake, and slower when you're sleeping. There are also normal patterns to these waves. These frequencies and patterns are what the EEG reader looks for.


ABNORMAL An abnormal EEG may consist of: Abnormal changes in normal rhythm:  If asymmetrical, the side with lower amplitude is usually pathological  Abnormal slow activity:  A sensitive indicator of encephalopathy if diffuse; correlate with regional cerebral dysfunction if localized; may appear as intermittent rhythmic delta (FIRDA in adult or OIRDA in children) Distinctive abnormal pattern:  Regular repetition of spikes, sharp waves, slow waves or any of the combination  e.g. PLED, burst suppression, triphasic waves, pseudoperiodic generalized sharp waves in CJD, pseudoperiodic slow complexes in HSV encephalitis Epileptiform discharges:  Spikes, polyspikes, sharp and slow waves


FACTORS Factors affecting EEG interpretation Age:  maturation of EEG  Arousal:  refers to different sleep stages Medicatio n s  e.g. benzodiazepines Pathological brain condition  (e.g.craniotomy) Environment  e.g. a.c. interference, ICU setting Quality of recording  – aware of artifacts

normal :

normal generalized seizure

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