EEG Non-Epileptiform Abnormalities 4 — Questions and Answers
Question 1: Which EEG pattern is characterized by diffuse slowing that waxes and wanes and is classically associated with hepatic encephalopathy?
- Triphasic waves (Correct answer)
- Burst suppression
- FIRDA
- Beta spindles
Correct answer: Triphasic waves
Triphasic waves are bilaterally synchronous, frontally dominant, high-amplitude slow waves classically seen in hepatic encephalopathy and other toxic-metabolic states.
Question 2: FIRDA (Frontal Intermittent Rhythmic Delta Activity) is most commonly associated with which condition?
- Focal cortical lesion
- Diffuse encephalopathy or deep midline dysfunction (Correct answer)
- Temporal lobe epilepsy
- Normal variant in elderly
Correct answer: Diffuse encephalopathy or deep midline dysfunction
FIRDA reflects diffuse cerebral dysfunction or deep midline/diencephalic disturbance and is not a focal or epileptiform finding.
Question 3: A burst suppression pattern on EEG is most consistent with which clinical scenario?
- Stage II sleep in a healthy adult
- Severe diffuse cerebral dysfunction such as deep anesthesia or anoxic brain injury (Correct answer)
- Focal temporal lobe lesion
- Benign rolandic epilepsy
Correct answer: Severe diffuse cerebral dysfunction such as deep anesthesia or anoxic brain injury
Burst suppression indicates severely depressed cerebral activity and is seen with deep anesthesia, hypothermia, or severe anoxic-ischemic encephalopathy.
Question 4: Which EEG finding is considered a non-epileptiform abnormality that reflects cortical dysfunction ipsilateral to a structural lesion?
- Focal polymorphic delta slowing (Correct answer)
- Occipital dominant rhythm at 10 Hz
- Lambda waves
- Sleep spindles
Correct answer: Focal polymorphic delta slowing
Focal polymorphic delta activity indicates underlying structural or physiologic disruption of cortical neurons in that region and is not epileptiform.
Question 5: Electrocerebral inactivity (ECI) on EEG requires that no cerebral electrical activity exceed what amplitude threshold?
- 5 µV
- 10 µV
- 2 µV (Correct answer)
- 20 µV
Correct answer: 2 µV
ECI is defined as no electrical activity over 2 µV recorded with electrode impedances under 10 kΩ using high-sensitivity settings and standard interelectrode distances.
Question 6: Which pattern is characterized by generalized, bisynchronous rhythmic delta activity seen predominantly over posterior head regions and is a non-epileptiform finding?
- OIRDA (Occipital Intermittent Rhythmic Delta Activity) (Correct answer)
- PLED
- GRDA
- Hypsarrhythmia
Correct answer: OIRDA (Occipital Intermittent Rhythmic Delta Activity)
OIRDA consists of occipitally predominant rhythmic delta bursts, is associated with encephalopathy or posterior fossa lesions, and is not inherently epileptiform.
Question 7: In a comatose patient, the presence of sleep architecture elements such as sleep spindles or K-complexes on EEG suggests which prognostic implication?
- Certain poor outcome
- Relatively preserved thalamocortical function and potentially better prognosis (Correct answer)
- Imminent seizure activity
- Electrocerebral inactivity
Correct answer: Relatively preserved thalamocortical function and potentially better prognosis
Preservation of sleep architecture in coma indicates intact thalamocortical circuitry and generally correlates with a more favorable neurological prognosis.
EEG Non-Epileptiform Abnormalities 4
Which EEG pattern is characterized by diffuse slowing that waxes and wanes and is classically associated with hepatic encephalopathy?