EEG Abnormal Epileptiform Patterns 2 — Questions and Answers
Question 1: Which EEG pattern is characterized by a spike followed by a slow wave complex occurring at approximately 3 Hz?
- Hypsarrhythmia
- Generalized 3 Hz spike-and-wave (Correct answer)
- Periodic lateralized epileptiform discharges
- Burst suppression
Correct answer: Generalized 3 Hz spike-and-wave
The classic 3 Hz spike-and-wave pattern is the hallmark of childhood absence epilepsy, appearing as generalized, synchronous, bilateral discharges.
Generalized 3 Hz spike-and-wave complexes are the electrographic signature of typical absence seizures. These discharges are bilaterally synchronous and symmetric, arising from thalamocortical circuits. They typically begin and end abruptly and are enhanced by hyperventilation. Hypsarrhythmia is seen in infantile spasms, PLEDs are focal periodic discharges, and burst suppression reflects severe encephalopathy.
Question 2: What is the typical duration criterion for an EEG spike?
- Less than 20 milliseconds
- 20 to 70 milliseconds (Correct answer)
- 70 to 200 milliseconds
- 200 to 500 milliseconds
Correct answer: 20 to 70 milliseconds
By IFCN definition, a spike has a duration of 20 to 70 milliseconds, distinguishing it from sharp waves which last 70 to 200 milliseconds.
The International Federation of Clinical Neurophysiology (IFCN) defines spikes as transient waveforms lasting 20 to 70 milliseconds that are clearly distinguished from background activity. Sharp waves are similar in morphology but longer, lasting 70 to 200 milliseconds. Both are considered epileptiform when they disrupt the background, have a sharp contour, and are followed by a slow wave. Waveforms under 20 ms are typically muscle artifact.
Question 3: Periodic lateralized epileptiform discharges (PLEDs) are most commonly associated with which condition?
- Metabolic encephalopathy
- Acute structural brain lesion such as stroke (Correct answer)
- Benign childhood epilepsy
- Normal drowsiness
Correct answer: Acute structural brain lesion such as stroke
PLEDs (now called lateralized periodic discharges or LPDs) are strongly associated with acute destructive brain lesions, most commonly stroke, and may indicate ongoing seizure activity.
Lateralized periodic discharges (LPDs, formerly PLEDs) consist of repetitive sharp or spike-and-wave complexes occurring at regular intervals (0.5-2 Hz), typically focal or hemispheric. They are most commonly associated with acute structural lesions such as ischemic stroke, hemorrhage, or herpes encephalitis. They carry a high risk of seizures (up to 80%). While metabolic encephalopathy can produce generalized periodic discharges (GPDs), lateralized patterns point to focal pathology.
Question 4: Which epileptiform pattern consists of high-amplitude, chaotic, multifocal spikes and slow waves seen in infantile spasms?
- Generalized polyspike-and-wave
- Hypsarrhythmia (Correct answer)
- Electrical status epilepticus in sleep
- Focal cortical dysplasia pattern
Correct answer: Hypsarrhythmia
Hypsarrhythmia is the classic interictal EEG pattern of infantile spasms (West syndrome), characterized by high-amplitude disorganized slow waves with multifocal spikes.
Hypsarrhythmia is defined by high-amplitude (>200 µV) slow waves intermixed with multifocal, asynchronous spikes and sharp waves with no consistent pattern or organization. It is the interictal hallmark of West syndrome (infantile spasms). During clinical spasms, the EEG may show an electrodecremental response. Treatment with ACTH or vigabatrin can lead to resolution of the pattern. The chaotic, high-voltage nature distinguishes it from other generalized epileptiform patterns.
Question 5: What feature best distinguishes a benign epileptiform transient of sleep (BETS) from a pathological epileptiform discharge?
- BETS have a duration greater than 200 milliseconds
- BETS are typically small, isolated, and lack an after-going slow wave (Correct answer)
- BETS occur only during REM sleep
- BETS always appear in the frontal regions
Correct answer: BETS are typically small, isolated, and lack an after-going slow wave
BETS (also known as small sharp spikes or SSS) are low-amplitude, brief, isolated transients without after-going slow waves, occurring during drowsiness and light sleep, and are considered benign normal variants.
Benign epileptiform transients of sleep (BETS) are small sharp spikes, typically under 50 µV, with a brief duration and a characteristic lack of an after-going slow wave component. They occur during drowsiness and NREM stages I-II, often in temporal regions, and have no clinical significance. Pathological epileptiform discharges typically disrupt background activity, have higher amplitude, and are followed by slow waves. Recognizing BETS prevents misdiagnosis of epilepsy.
Question 6: Generalized periodic discharges (GPDs) at 1-2 Hz intervals with triphasic morphology are most characteristic of which condition?
- Juvenile myoclonic epilepsy
- Hepatic encephalopathy (Correct answer)
- Lennox-Gastaut syndrome
- Benign rolandic epilepsy
Correct answer: Hepatic encephalopathy
Triphasic waves appearing as generalized periodic discharges are classically associated with metabolic encephalopathies, particularly hepatic encephalopathy, though they can be seen in other toxic-metabolic states.
Triphasic waves are generalized periodic discharges with three phases — an initial negative deflection, a dominant positive sharp component, and a subsequent negative slow wave. They classically occur at 1-2 Hz with an anterior-to-posterior lag. While most associated with hepatic encephalopathy, they can also be seen in uremia, hypoglycemia, and other metabolic disturbances. Distinguishing triphasic waves from nonconvulsive status epilepticus can be challenging and may require a benzodiazepine trial.
EEG Abnormal Epileptiform Patterns 2
Which EEG pattern is characterized by a spike followed by a slow wave complex occurring at approximately 3 Hz?