Generalised Epileptiform Patterns Manori Wijayath Westmead Hospital, Sydney, Australia With slides from Elizabeth Walker and Andrew Bleasel Generalised Epilep-form Discharges: Outline 1. Generalised epilep.form pa2erns - interictal 2. Generalised paroxysmal pa2erns: OIRDA 3. Imitators: generalised non- epilep.form - Phantom spike and wave (6 Hz) 4. Generalised seizure discharges - ictal pa2erns 5. Causes of confusion: misleading aspects of EEG in generalised epilepsy
Generalised Epilep-form Pa:erns 1. 3 Hz spike and wave discharges 2. Polyspike and wave discharges 3. Slow spike and wave discharges 4. Generalised paroxysmal fast ac.vity 5. Photosensi.ve responses 6. Ictal Pa2erns Generalised Discharges Simultaneous, symmetric and synchronous in both hemispheres Equipoten.al at homotopic regions But no cerebral poten.al is equally expressed Asymmetries are common/ shiving lateraliza.on may begin 10-25ms earlier have maximal amplitude one hemisphere site of max shivs between hemispheres in record Fragmenta.on of Discharge
Criteria for Epilep-form Discharges VOLTAGE: High MORPHOLOGY: Shorter, lower amplitude first phase Longer, higher amplitude second phase Polyphasic AVer going slow wave DISTRIBUTION: Must have a physiologic field LOCATION & STATE: Unlike normal physiologic transients Different (stands out) from background POLARITY: Great majority are predominantly surface nega.ve
Interictal Epilep-form Pa:erns Defini-on Weir (1965) Spike of spike-wave complex three components: spike 1, positive transient, and spike 2, slow wave 1)spike 1, is negative in polarity, small in amplitude (25 50 uv), and short in duration (about 10 ms) 2) followed by a positive transient lasting 100 150 ms, which continues into; 3) Spike 2, the main negative component of the complex lasting 30 60 ms. 4) Dome- shaped surface nega.ve wave las.ng 150 200 ms
PATHOPHYSIOLOGY CHARACTERISTICS OF SWD Both human and animal data suggest; involvement of the thalamus and the cortex in the genera.on of SWD In IGE, Circadian varia.ons of generalized epilep.form discharges are well described Those discharges tend to occur more oven aver awakening and during cyclic alterna.ng pa2ern of non rapid eye movement sleep Yield increased by - Ac.va.on procedures; hyperven.la.on, intermi2ent pho.c s.mula.on, eye closure, and fixa.on- off Propaga-on of the SWC Spike and trough oven seen over the anterior and central regions Waves usually centrally distributed (Lemieux & Blume, 1986) Spike- wave complex seems to undergo morphologic changes during sleep - In non- REM sleep generalized SWD occur in isola.on or in shorter bursts at a slower (<3 Hz) frequency. - In stage III and stage IV non- REM sleep, polyspikes and irregular spike- wave discharges occur at a slower frequency (<3 Hz). The wave becomes longer in dura.on and distorted in morphology. - Fragmenta.on - In REM sleep, the discharges are rare yet similar in morphology to those in the waking state (Sato et al., 1973)
Fragmenta-on of Generalised Discharges Fragmenta.on occurs when the regular discharge beaks down Mul.ple spikes Irregular spike wave Slowing Occurrence Increase in drowsiness and sleep Very common in JME
Eg: NREM sleep in a 7- year- old pa.ent with absence seizures demonstra.ng a burst of polyspike- and- wave ac.vity (A) and fragmentary bursts of spike- andwave ac.vity (B) Frequency of SW Complexes < 2.5 Hz Atypical CAE 18% JAE 21% JME 3% 2.5-3.5 Hz Typical 3Hz CAE 75% JAE 55% JME 60% > 3.5 Hz Atypical, fast CAE 64% JAE 83% JME 57%
Generalised epilep-form discharges Frequency of discharge and dura-on Frequency of discharges In IGE frequency of discharge ranges from 2-6 Hz 1. Rela.vely constant within individuals 2. Ini.al frequency faster then slows Dura.on of interictal bursts 1. Similar within individuals 2. Associated with epilepsy syndrome - JME short seizures (4-6 secs) - CAE long seizures (10-12 secs) Associated with state - shorter in sleep 1. Typical 3 Hz Spike and Slow Wave Single complexes or bursts Complexes repeat at a frequency of 3 Hz High amplitude spike followed by slow wave ( dart and dome ) Maximal in mid- frontal region (F3, F4) Precipitated by hyperven.la.on (oven) Precipitated by pho.c s.mula.on (CAE 18%, JAE 8 %) Syndrome - idiopathic generalised epilepsy
1. Typical 3 Hz Spike and Slow Wave Effect of sleep NREM Increased burst frequency, decreased dura.on Complexes more irregular fragmented, and bursts of polyspike- and- wave ac.vity (Niedermeyer, 1965; Ross et al., 1966; Sato et al) Low voltage spike REM Decreased burst frequency Similar to complexes in awake state A2enua.on or cessa.on of SWD (Kellaway and Frost, 1983) Posterior rhythmic delta / OIRDA (15 %) Occipital intermi2ent rhythmic delta ac.vity 1. Typical 3 Hz Spike and Slow Wave
2. 4-5 Hz SWD Discharges SWD in older pa.ents and those with JME may be faster:3.5-6hz range 2 to 10 Hz 3. Polyspike and slow wave complexes Two or more symmetrical (poly)spikes associated with one or more high voltage irregular 2-5 Hz slow waves with intermixed spikes. 18-54% of IGE pa.ents, symptoma.c epilepsies Strong associa.on with myoclonic and absence seizures More common in drowsiness and sleep Occurs in fragments Usually noted at beginning of seizures but may con.nue or just be seen in body of seizure Polyspikes may occur in isola.on during eye closure, or sleep. Pho.c s.mual.on
3. Polyspike and slow wave complexes 3. Polyspikes
4. Generalised Slow Spike Wave OVen sharp and slow waves rather than spike and slow wave Frequency 1-2 Hz Prolonged runs with no clinical signs Diffusely distributed but may be seen in anterior regions Bilaterally symmetrical, but shiving asymmetries Background usually abnormally slow Associated in sleep with polyspike wave complexes, rhythmic 10-20 Hz waves and electrodecremental events Max incidence age 1-5 years Associated with Symptoma.c Generalised Epilepsy Syndromes Burst of frontal dominant 2 to 2.5 Hz slow spike- and- wave ac.vity associated with an atypical absence seizure, during which.me the pa.ent stared and was nonresponsive to name calling.
NREM sleep in an 11- year- old pa.ent with the Lennox- Gastaut syndrome 5. Irregular spike wave/atypical spike wave Paroxysms of spikes or sharp waves with or without slow waves and with an irregular frequency of 3 to 5 Hz. This pa2ern increases in frequency with age and is the most common pa2ern in older people
Distribu-on of generalised epilep-form pa:erns across age group H Aurlien et al Clinical Neurophysiology 120 (2009) 3-10 Photoparoxysmal Response (PPR) Occurrence of spikes or spike waves in response to intermi2ent pho.c s.mula.on. Epilep.form discharge may persist aver end of pho.c s.mulus. Majority of pa.ents have stable photosensi.ve range 14-18 Hz Can be an asymptoma.c finding - PPR present in 7.6% of healthy children. - Healthy young males, 0.5% had unequivocal epilep.form discharges 58% occurring only on pho.c s.mula.on. Occurs in around 5% of pa.ents with epilepsy - Important feature in metabolic diseases or epilep.c encephalopathies (progressive myoclonic epilepsies, Dravet Syndrome) - Idiopathic occipital lobe epilepsies - Idiopathic generalised epilepsies, especially JME. MC females
Photoparoxysmal Response (PPR) Distribu.on of PPR across age group (H Aurlien et al Clinical Neurophysiology 120 (2009) 3-10) Imitators; Generalised non- epilep-c spike wave: 6 Hz Spike and Slow Wave ALMOST ALWAYS 6 HZ Brief bursts LOW AMPLITUDE spike with strong posi.ve component High amplitude wave with wide distribu.on Posterior or anterior maximum Relaxed wakefulness and drowsiness; DISAPPEARS in Stage 2 sleep More easily seen in referen.al montages Not an indicator of epilepsy
6 Hz Spike and Slow Wave 2 main pa:erns W: waking H: high amplitude A: anterior M: males F: female O: occipital L: low amplitude D: drowsy 6 Hz spike wave during drowsiness FOLD
6 Hz Spike Wave WHAM Generalised Paroxysmal Non- epilep-form Pa:erns Occipital Intermi2ent Rhythmic Delta Ac.vity: OIRDA 2-4 Hz rhythmic ac.vity Bioccipital, but can have field to parietal and temporal areas Blocked by pho.c, aler.ng, and eye opening Enhanced by HV and drowsiness; not seen in sleep
Occipital Intermi:ent Rhythmic Delta Ac-vity OIRDA Common in CAE (33%) and also seen in JAE Can occur in long runs (minutes) Not an ictal pa2ern Good prognos.c feature in CAE Children who have 3 Hz spike wave and OIRDA have a be2er than 50% chance of spontaneous remission Children with 3 Hz spike wave, no OIRDA, but who have photoparoxysmal responses are more likely to develop tonic- clonic seizures and only 6% will have spontaneous remission Occurs occasionally in children without absence seizures: head trauma, migraine, toxic encephalopathy 5 year old girl, clinical absence and 3 Hz spike wave and OIRDA
Generalised Epilep-form Pa:erns- Interictal vs Ictal Ictal pa2erns oven represent longer repe..ons of interictal pa2erns Dis.nc.on less clear cut for certain generalised pa2erns (spike- wave) compared with focal pa2erns Presence of clinical signs depends on length of burst, persistence of spike component, adequate tes.ng during the burst Ictal pa:erns Widely varying types of transi.on from interictal to ictal 1. Burst of repe..ve epilep.form discharges, eg 3 Hz SW 2. Bilaterally synchronised rhythmic discharge, 80% > 15Hz (GPFA) 3. Alpha range rhythm less common 4. Abrupt a2enua.on of voltage eg tonic, electrodecremental seizures
Ictal pa:ern 1: burst of repe--ve spike wave 3 Hz - CAE Ictal pa:ern 2: bilaterally synchronous rhythmic discharge Generalised paroxysmal fast ac-vity
Seizure in evolu-on Absence seizure >>>>>>>>>>>>>>>>>>>>>>>>>>>>>GTCS>>>>>>>>>>>>>>>>> Ictal pa:ern 4: electrodecrement
Ictal pa:ern 4: electrodecrement (LGS) Focal Pa:erns with Generalised Features Focal discharges may have a field over both hemispheres, oven where there is a dipole crossing hemispheres Maximal nega.vity remains fairly constant Persis.ng unilateral asymmetries and/or unilateral discharges preceding generalised spike wave may suggest focal onset Tip: use montage and cursors and to determine if discharge focal or generalised eg transverse, referen.al
Lec frontal epilep-form discharges Secondary Bilateral Synchrony Simple concept but in reality difficult and disputed Mesial or inferior frontal focus causing bilateral synchronous discharges Usually irregular and slow discharges, not classical spike wave Single phase reversal at or adjacent to the midline By contrast, 3 Hz spike and wave double phase reversal at F3 and F4
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