Non-Epileptiform Activity, Encephalopathies, and Coma Lecture Notes

Flashcards covering non-epileptiform EEG patterns, various encephalopathies (metabolic, uremic, toxic, endocrine), coma patterns (alpha, theta, spindle, delta), and periodic discharges (PLEDs, GPEDs, SIRPIDs).

Non-epileptiform Activity

EEG activity that denotes underlying cortical electrophysiological dysfunction due to an organic cause; it is less specific than epileptiform activity and must be interpreted against age and state (awake, drowsy, sleep).

Breech Rhythm

Unfiltered high-voltage physiological, fast waveforms with a spiky and irregular morphology, typically appearing over skull defects.

Focal Attenuation

Reduced amplitude of a specific type of frequency activity indicating a focal cortical lesion, reversible dysfunction (post-ictal), or collections like hematomas and tumors between the cortex and electrode.

Suppression

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

Theta Frequency

Slow waves occurring in the frequency range of $5-7\,Hz$.

Delta Frequency

Slow waves occurring in the frequency range of $1-4\,Hz$.

Generalised Asynchronous Slowing

Slowing $< 8\,Hz$ occurring over both hemispheres with no constant relationship between different regions; the repetition varies by $2-3\,Hz$.

FIRDA

Frontal Intermittent Rhythmic Delta Activity; bilateral, intermittent, synchronous delta waves with a frontal maximum in adults.

OIRDA

Occipital Intermittent Rhythmic Delta Activity; bilateral, intermittent, synchronous delta waves with an occipital maximum in children.

TIRDA

Temporal Intermittent Rhythmic Delta Activity; rhythmic monomorphic temporal delta strongly associated with temporal lobe epilepsy and useful as a lateralising feature.

Continuous Slow Activity

Irregular (polymorphic) delta or theta waves that are non-responsive to external stimuli and indicate severe disturbances of interneuronal connections.

Triphasic Waves

Large amplitude ($150-300\,\mu V$) waves with a negative sharp phase, a broad positive phase, and a larger negative slow wave, typically showing a frontal-occipital phase lag of $25-140\,msec$.

Beta Coma

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

GPDs (Generalized Periodic Discharges)

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

PLEDs

Periodic Lateralized Epileptiform Discharges; sharp transients appearing in a periodic or semi-periodic fashion associated with acute cerebral insults like stroke or fast-growing tumors.

SSPE (Subacute Sclerosing Panencephalitis)

A fatal measles sequel developing $7-10\,years$ after infection, characterized by high amplitude ($300-1500\,\mu V$) periodic complexes recurring every $4-15\,seconds$.

SIRPIDs

Stimulus-Induced Rhythmic, Periodic or Ictal Discharges; periodic or ictal-appearing discharges consistently induced by alerting stimuli like auditory cues or sternal rub.

Alpha Coma

Predominant non-reactive alpha activity ($8-13\,Hz$) with an anterior maximum in an unconscious patient, often due to ponto-mesencephalic lesions or severe anoxia.

Spindle Coma

EEG pattern resembling sleep spindles ($9-14\,Hz$) in an unconscious patient, suggesting impairment of ascending reticular activating pathways with sparing of thalamocortical circuits.

Burst Suppression

Cyclical cycles of brain activity bursts (sharp waves/spikes) followed by periods of absent or severely attenuated activity ($< 10\,\mu V$).

Electrocerebral Inactivity (ECI)

The absence of EEG activity over $2\,\mu V$ when recording from scalp electrode pairs at least $10\,cm$ apart with interelectrode impedances between $100$ and $10,000\,Ohms$.