• Definition:Any activity which does not correlate with the age and state of the patient.Abnormality could be of the following two main types of activity.1. Non epileptiform Abnormal pattern2. Epileptiform Pattern
1. Non Epileptiform Abnormal PatternNon epileptiform abnormal pattern consists of the following types.1. Slow waves2. Asymmetry (Amplitudes & Frequency)1. Slow wavesSlow waves are further divided into two typesFocal slow wavesDiffuse slowing
Slow waves1-focal slowing :Focal slowing means if slowing is restricted to only one hemisphere or specific region .The most prominent focal slowing is delta activity which ranges 0.5 – 3.5 Hz.Focal slowing may be continuous or intermittent.Continuous focal delta slowing is usually due to localized structural lesion (e.g tumor, stroke, abscess)Intermittent focal polyrhythmic delta slowing is non specific and could be due to migraine, trauma, post-ictal dysfunction etc.
Diffuse slowing:Diffuse slowing/generalized slowing means synchronous and symmetrical slowing that appears in the whole background throughout the recording which indicates the involvement of both hemispheres of the brain or cerebral dysfunction.While reporting diffuse slowing, age, state (alertness) and medications of the patient must be known.
2. Asymmetry (Amplitudes & Frequency)Asymmetric background could be amplitude-wise or frequency-wise.More than 50% amplitude wise asymmetry and 1 or more than 1% frequency wise asymmetry throughout the recording is considerable and it shows hemispheric abnormality, considering the age and state of the patient.
2. Epileptiform abnormal patternEpileptiform activity mainly consists of spike and sharp waves.Spike : A transient clearly distinguished from the background activity with pointed peak, duration from 20-70 ms mostly followed by slow wave.• Sharp wave :• A transient which is clearly distinguished from the background activity with pointed peak, duration from 70-200ms.
Types of epileptic abnormal activities1. Focal epileptiform activity: Focal epileptiform activity (spike and sharp waves) consists of spike and sharp waves that appear on one or a few neighboring electrodes.2. Generalized epileptiform activity: Epileptiform discharges (spike and sharp waves) that appear over most of all parts of both hemisphere and usually have symmetrical shape, amplitude and timing in corresponding areas.
Types of Epileptiform patterns Types of Epileptiform patternsEpileptiform abnormalities can be divided in to following basic abnormal EEG patterns.• Benign rolandic epilepsy (BRE)• 3/sec spike and wave.• Periodic lateralized epileptiform discharges (PLEDS).• Triphasic sharp waves• Sub acute sclerosing panencephalities (SSPE)• Lennox gastaut syndrome (LGS)• Hypsarrythmia (West Syndrome)• Creutzfeldt-Jakob disease (CJD)
1. Benign Rolandic Epilepsy (BRE)Rolandic epilepsy (RE) is the most common human epilepsy, affecting children between 3 and 12 years of age, boys more often than girls (3:2).Focal sharp waves in the centro-temporal area define the syndrome, are a feature of several related childhood epilepsies and are frequently observed in common developmental disorders (e.g, speech dyspraxia (difficulty) , attention deficit hyperactivity disorder and developmental coordination disorder).Onset – Usually 4-10 years , may persist till 12 years.• May be unilateral or bilateral.Sz timing – Mostly increased in light sleep.• Reference: • Genetic evaluation and counseling for epilepsy • Nature Reviews Neurology Review (01 Aug 2010)
2. 3/Sec Spike and WaveThe three Hz spike and wave pattern is suggestive of idiopathic Gen. epilepsy• Characteristics• It is classically described with typical absence epilepsies when bursts of 3Hz spike and wave is Gen, regular, symmetrical, synchronous and maximal in the anterior head region with clinically fluttering of eyes and automatism. It usually occurs in patients aged b/w 5-12 years. Onset 2 years and can be appeared till 14 years. Often faster at onset and slows down toward end. Accentuated (more prominent) by HV (50-80% pt) and
3. Periodic Lateralized Epileptic Discharges (PLEDs)PLEDs are basically triphasic with sharply contoured wave followed by a slow wave mostly occurring unilaterally with duration 100-300 msec and amplitude 100-300 often present with fast rhythm b/w discharges.Characteristics:• Periodic recurrence every 0.5-4.0 sec.• With frequency of 1-2 sec.• Etiology (Cause)• acute infarction, CVA, tumor, anoxia and herpes simplex encephalitis, abscess etc.
pledsPeriodic lateralized epileptiform discharges (PLEDS), regional left centrotemporal. The repetitive discharges occur with a periodicity of about 1 second
4. Triphasic sharp wavesThese are typical and sharply contoured wave discharges.CharacteristicsHaving three phase +, -ve and then +ve.• Initial is sharp component.• Appeared with rhythmic train of 1.5-2.5 /sec.• Having medium to high voltage (>70uv) .• Bilaterally synchronous and symmetrical• These waves are having anterior posterior lag of 25-140 sec.• Best seen in referential montage.• Appeared in hypoxic state, subdural hematoma, intoxication (excite by the action of a chemical substance ), mainly in hepatic encephalopathy.• Seen in deep impairement of consciousness but occasionally in
5. Sub acute sclerosing panencephalities (SSPE)Characteristics• Repetitive bursts of high voltage spike, sharp and slow wave complexes, recurring after every 4-15 seconds.• More prominent in awaking state.• It relates with measles and myoclonic jerks• Gen. but maximum over fronto central areas.• Frequency ranges 4-15/sec
SSPE (Cont’d)• All the waves are Stereotyped (morphologically similar)• Bilaterally synchronous• Periodic high voltage 300-1500uv of sharp and slow waves complex with an irregular delta wave superimposed.• It is an inflammatory disease that occurs in children and adolescents and is believed to be caused by measles virus.
7. Hypsarrythmia (West Syndrome)Hypsarrhythmia is an abnormal pattern, consisting of high amplitude and irregular paroxysmal sharp wave, spike, poly spikes, independent, multifocal and focal spike on all cortical region with a background of chaotic (disorderly) and disorganized activityIt is a pattern seen in patient with infantile spasm• Hypsarrhythmia is frequently found in patients with West syndrome .• Appeared at the age of 4-6 or 13 months.• Clinically patient is mentally and physically retarded.• Also diffuse slowing is present.
6. Lennox gastaut syndrome (LGS)• It is the disease of the later phase of hypsarrythmia which usually shows slow spike and wave discharges and may show discharges of gen spikes.• Duration 2.5/sec or less.• The discharges may be Gen and synchronous• Highest amplitudes in midline frontal region (Fz).• The discharges may become continuous during sleep.• Patient gradually becomes mentally retarded.• Within the age of 11-12 years most of the patients die, but some may live upto 20 years, depending on the affecting of syndrome.
8. Creutzfeldt-Jakob disease (CJD)• CJD is at times called a human form of mad cow disease In which the brain tissue develops holes and takes on a sponge-like texture. This is due to a type of infectious protein called a prion.• Prions are misfolded proteins which replicate by converting their properly folded counterparts.• CLINICAL SYMTOMS:• Symptoms of CJD are rapidly progressive dementia, leading to memory loss, personality changes and hallucinations.
(CJD) cont’d• This is accompanied by physical problems such as speech impairment, jerky movements (myoclonus), balance and coordination dysfunction (ataxia), changes in gait, rigid posture, and seizures.EEG FINDINGS:• Periodic discharges with sharp wave or a sharp triphasic complex.• 100 -300msec duration• Repetition rate of 0.5-2/sec.• Shows severely disorganized & generalized synchrony background.• Some cases show unilateral discharges over one