Abnormal EEG Abnormal EEG

BY:BY:

Ejaz karimEjaz karimNeurophysiology TechnologistNeurophysiology Technologist AKUH. AKUH.

Definition:

Any activity which does not correlate with the age and state of the patient.

Abnormality could be due to the following two main types of activity.

1. Non epileptiform Abnormal pattern/activity

2. Epileptiform Pattern/activity

Non epileptiform abnormal pattern consists of the following types.

1. Slow waves Slow waves are further divided into

two typesFocal slow wavesDiffuse slowing

2. Asymmetric background (Amplitudes & Frequency)

1-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/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.

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.

Epileptiform 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.

1. 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.

Epileptiform 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)

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 EEG trait for the syndrome, are a feature of several related childhood epilepsies and are frequently observed in common developmental disorders (eg, speech dyspraxia (difficulty) , attention deficit hyperactivity disorder and developmental coordination disorder).

(fronto-central +, centro-temporal -)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)

The three Hz/sec 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 photic stimulation (about 20% of pt).

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.

These are typical and sharply contoured wave discharges.

CharacteristicsHaving three phases +ve, -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, mainly in hepatic encephalopathy and liver failure.

Seen in deep impairment of consciousness but occasionally in awake state.

Triphasic sharp wavesTriphasic sharp waves

CharacteristicsRepetitive bursts of high voltage

polyspike and sharp and slow wave complexes, recurring after every 4-15 seconds.

More prominent in awaking state. It relates with measles and myoclonic jerksGen. but maximum over fronto central

areas.Frequency ranges 4-15/sec

All the waves are Stereotyped (morphologically similar)

Bilaterally synchronousPeriodic 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.

Stereotyped high amplitude periodic complexes in an adolescent female with subacute sclerosing pan-encephalitis.

It is the disease of the initial phase of hypsarrythmia which usually shows slow spike and wave discharges and also called petit mal variant.

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 patient dies. Patient with LGS shows slow various seizures with

discharges of gen spike, slow spike, rapid spike etc.

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 activity

It 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.

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.

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

hemispheres.

Classic example is Juvenile Myoclonic Epilepsy (JME) Characterstics of the discharges

Bursts of bisynchronous, symmetric polyspikes with maximal voltage over frontal and central regions

Follwed by high voltage irregular slow waves intermixed with spikes

Fast repetition rate 25% of the patients EEG shows typical 3Hz spike

and wave complexes

Typically described with Lennox Gestaut syndrome

Characteristics Bilateral, synchronous, symmetric, high

voltage discharges which are maximally expressed over frontocentral regions

Repetition rate is slow and erratic, ranging between 1-4 Hz