Non-Epileptiform Activity, Encephalopathies, and Coma in EEG

Flashcards covering non-epileptiform EEG patterns, encephalopathy grading, specific disease signatures (CJD, SSPE), and coma patterns.

Non-epileptiform Activity

EEG activity that is less specific than epileptiform activity and, if abnormal, denotes underlying cortical electrophysiological dysfunction due to an organic cause.

Asymmetry of Posterior Background Rhythm (Alpha)

Clinically significant if the right is greater than $50\%$ higher than the left, or if the left is greater than $35-50\%$ higher amplitude than the right.

Breech Rhythm

Unfiltered high-voltage physiological, fast waveforms, sometimes with a spiky and irregular morphology, typically seen in the presence of a skull defect.

Focal Attenuation

Reduced amplitude of one type of activity at a certain frequency indicating a focal cortical lesion or reversible cortical dysfunction, such as a post-ictal state.

Suppression

A state worse than attenuation indicating the complete or nearly complete disappearance of electroencephalographic activity.

Generalized Asynchronous Slowing

Slowing less than $8\,Hz$ occurring over both hemispheres with no constant relationship between different regions; the least specific abnormal finding in adults.

FIRDA

Frontal Intermittent Rhythmic Delta Activity; bilateral, intermittent, synchronous activity with frontal maximum distribution in adults.

OIRDA

Occipital Intermittent Rhythmic Delta Activity; bilateral, intermittent, synchronous activity with occipital maximum distribution in children.

TIRDA

Temporal Intermittent Rhythmic Delta Activity; rhythmic monomorphic temporal delta strongly associated with temporal lobe epilepsy and useful for lateralization.

Triphasic Waves

Large amplitude ($150-300\,\mu V$) waveforms consisting of a negative sharp wave, a broad positive phase, and a larger negative slow wave, typically with anterior predominance.

Dialysis Disequilibrium Syndrome

A condition occurring during or post-dialysis due to osmotic/electrolyte changes, characterized by bursts of rhythmic delta and theta on EEG.

Beta Coma

Generalized $12-16\,Hz$ background activity maximally seen over frontal regions in an unconscious patient, often caused by medications (barbiturates/benzodiazepines) or brainstem lesions.

Alpha Coma

Predominant alpha activity ($8-13\,Hz$) in a comatose patient that is typically non-reactive and has an anterior maximum.

Spindle Coma

EEG activity in an unconscious patient resembling symmetric $9-14\,Hz$ sleep spindles, suggesting preservation of thalamocortical circuits.

Burst Suppression

Presence of activity bursts (sharp waves/spikes) followed by cyclical periods of marked depression or absent activity, indicating severe cerebral dysfunction.

GPEDs (Generalised Periodic Epileptiform Discharges)

Periodic discharges occurring in up to $20\%$ of coma patients with severe post-anoxic encephalopathy, typically occurring within $12-48\,h$ after resuscitation.

PLEDS (Periodic Lateralized Epileptiform Discharges)

Periodic or semi-periodic sharp transients (spikes or sharp waves) that are lateralized or focal, usually associated with acute cerebral insults like CVAs or tumors.

Creutzfeldt-Jakob Disease (CJD) EEG Pattern

Characterized by Periodic Sharp Wave Complexes (PSWC) with a duration of $100-300\,msec$ and recurrence intervals of $0.7-1.5\,sec$.

SSPE (Subacute Sclerosing Panencephalitis) Pattern

High amplitude ($300-1500\,\mu V$) polyphasic complexes recurring every $4-15\,sec$, often showing a $1:1$ relationship with myoclonic jerks.

SIRPIDs

Stimulus-induced rhythmic, periodic, or ictal discharges; patterns consistently elicited by alerting stimuli like auditory cues or sternal rub.

Mild Encephalopathy

EEG grading where a posterior dominant and reactive background is present, but the frequency is too slow for the patient's age (theta frequency).

Moderate Encephalopathy

EEG grading characterized by poorly reactive theta and delta frequencies and the absence of a posterior background.

Severe Encephalopathy

EEG grading characterized by non-reactive moderate to high amplitude delta, periodic patterns, coma patterns, or burst suppression.

Electrocerebral Inactivity (ECI/ECS)

No EEG activity over $2\,\mu V$ when recording from scalp electrode pairs at least $10\,cm$ apart for at least $30\,minutes$.