Characteristic EEG pattern in Absence seizures?
Ans. A. 3-Hz spike-and-waves. (Ref. H - 17th/pg. 2498-2500, 2504-2505; 444).Harrison's 17th/pg. 2549......."The electrophysiologic hallmark of typical absence seizures is a generalized, symmetric, 3-Hz spike-and-wave discharge that begins and ends suddenly, superimposed on a normal EEG background"Absence Seizures (Petit Mai)# "The electrophysiologic hallmark of typical absence seizures is a generalized, symmetric, 3-Hz spike-and-wave discharge that begins and ends suddenly, superimposed on a normal EEG background".# Periods of spike- and-wave discharges lasting more than a few seconds usually correlate with clinical signs, but the EEG often shows many more brief bursts of abnormal cortical activity than were suspected clinically.# Hyperventilation tends to provoke the electrographic discharges and even seizures and is used during EEG.# The episodic generalized spike-wave activity that occurs during and between seizures in patients with typical absence epilepsy contrasts with focal interictal epileptiform discharges or ictal patterns found in patients with complex partial seizures.Atypical Absence Seizures# have features that deviate both clinically and electrophysiologically from typical absence seizures.# For example, the lapse of consciousness is usually of longer duration and less abrupt in onset and cessation, and the seizure is accompanied by more obvious motor signs that may include focal or lateralizing features.# The EEG shows a generalized, slow spike-and-wave pattern with a frequency of <2-5/s, as well as other abnormal activity.Complex Partial Seizures# The routine interictal (i.e., between seizures) EEG in patients with complex partial seizures is often normal or may show brief discharges termed epileptiform spikes, or sharp waves.# Since complex partial seizures can arise from the medial temporal lobe or inferior frontal lobe, i.e., regions distant from the scalp, the EEG recorded during the seizure may be nonlocalizing.Generalized, Tonic-Clonic Seizures (Grand Mai)# The EEG during the tonic phase of the seizure shows a progressive increase in generalized low-voltage fast activity, followed by generalized high-amplitude, polyspike discharges.# In the clonic phase, the high-amplitude activity is typically interrupted by slow waves to create a spike-and-wave pattern. The postictal EEG shows diffuse slowing that gradually recovers as the patient awakens.Atonic Seizures# Atonic seizures are characterized by sudden loss of postural muscle tone lasting 1-2 s. Consciousness is briefly impaired, but there is usually no postictal confusion.# A very brief seizure may cause only a quick head drop or nodding movement, while a longer seizure will cause the patient to collapse. This can be extremely dangerous, since there is a substantial risk of direct head injury with the fall.# The EEG shows brief, generalized spike-and-wave discharges followed immediately by diffuse slow waves that correlate with the loss of muscle tone.Myoclonic Seizures# Myoclonus is a sudden and brief muscle contraction that may involve one part of the body or the entire body.# A normal, common physiologic form of myoclonus is the sudden jerking movement observed while falling asleep. Pathologic myoclonus is most commonly seen in association with metabolic disorders, degenerative CNS diseases, or anoxic brain injury.# Although the distinction from other forms of myoclonus is imprecise, myoclonic seizures are considered to be true epileptic events since they are caused by cortical (versus subcortical or spinal) dysfunction.# The EEG may show bilaterally synchronous spike-and-wave discharges synchronized with the myoclonus, although these can be obscured by movement artifact.LENNOX-GASTAUT SYNDROMELennox-Gastaut syndrome occurs in children and is defined by the following triad:1) multiple seizure types (usually including generalized tonic-clonic, atonic, and atypical absence seizures);2) an EEG showing slow (<3 Hz) spike-and-wave discharges and a variety of other ab- normalities; and3) impaired cognitive function in most but not all cases.Partial (focal) seizuresAffect one area of the brain. Most commonly originate in medial temporal lobe. Often preceded by seizure aura; can secondarily generalize. Types:# Simple partial (consciousness intact)-- motor, sensory, autonomic, psychic# Complex partial (impaired consciousness).Generalized seizuresDiffuse. Types:# Absence (petit mal)--3 Hz, no postictal confusion, blank stare# Myoclonic--quick, repetitive jerks# Tonic-clonic (grand mal)--alternating stiffening and movement# Tonic--stiffening# Atonic--"drop" seizures (fails to floor); commonly mistaken for faintingAdditional Educational points:EEG:# NORMAL:- The frequencies most brain waves range from are 0.5-500 Hz; imp categories are-* Alpha waves - 8-13 Hz* Beta waves - Greater than 13 Hz* Theta waves - 3.5-7.5 Hz* Delta waves - 3 Hz or less- In normal awake adults lying quietly with the eyes closed, an 8- to 13-Hz alpha rhythm is seen posteriorly in the EEG, intermixed with a variable amount of generalized faster (beta) activity (>13 Hz); the alpha rhythm is attenuated when the eyes are opened. During drowsiness, the alpha rhythm is also attenuated; with light sleep, slower activity in the theta (4-7 Hz) and delta (<4 Hz) ranges becomes more conspicuous.Some more Specific diagnostic patterns of EEG: PatternDiagnostic ofComments1Periodic lateralizing epileptiform discharges (PLEDs)acute focal cerebral insult like HSVif bilateral diagnostic of HSV2Periodic high voltage with 4-15 secs separation with accompanying body jerks, no change with painful stimulation.Pathognomoic of SSPEd/d is PCP overdose3Myoclonic jerks with bilateral sharp wave 1.5-2 / secs (early = slowing; later=triphasic).Creutzfeldt Jakob diseaseMay resemble PLEDs, but contrary to them in CJD are not reactive to painful stimuli.4Triphasic wavesMay be seen in hepatic enceph, postanoxia, hyponatremiaNot a specific pattern
3-Hz spike-and-waves
l-2Hz spike-and-waves
Generalized polyspikes
Hypsarrythmia
C.N.S.