EEG - Electroencephalography Non-Epileptiform Abnormalities Questions and Answers 1 — Questions and Answers
Question 1: An EEG recording from a 55-year-old patient in a drowsy state shows bilateral, synchronous, rhythmic 5-7 Hz sharply contoured waves over the parietal and posterior temporal regions. The pattern has an abrupt onset and offset, lasts for approximately 45 seconds, and does not evolve in frequency or morphology. The patient remains unresponsive to auditory stimuli during the event. Which of the following non-epileptiform patterns is most likely being observed?
- Rhythmic Mid-Temporal Theta of Drowsiness (RMTD)
- Subclinical Rhythmic Electrographic Discharge of Adults (SREDA) (Correct answer)
- Wicket Spikes
- 14 & 6 Hz Positive Spikes
Correct answer: Subclinical Rhythmic Electrographic Discharge of Adults (SREDA)
Subclinical Rhythmic Electrographic Discharge of Adults (SREDA) is characterized by bilateral, widespread, rhythmic, and sharply-contoured theta activity with a parietal-posterior temporal maximum. It has an abrupt onset/offset, does not evolve, and occurs without any clinical symptoms, fitting the description perfectly. [14, 25] RMTD is typically mid-temporal and shorter in duration. [2, 8] Wicket spikes are arc-shaped and occur in the temporal regions, often independently. [2, 35] 14 & 6 Hz positive spikes have a different frequency and morphology.
Question 2: A 68-year-old patient with a history of a craniotomy for a meningioma resection presents for a routine EEG. The recording shows a focal area of high-amplitude, sharp, and at times spiky-appearing 6-11 Hz activity directly over the surgical site. This activity is persistent across both awake and drowsy states. Which feature would most strongly differentiate this as Breach Rhythm rather than an epileptiform abnormality?
- The presence of intermixed beta frequencies.
- The high amplitude of the activity compared to the contralateral side.
- Its focal and asymmetric nature.
- The absence of an after-going slow wave. (Correct answer)
Correct answer: The absence of an after-going slow wave.
A key distinguishing feature between Breach Rhythm and a true epileptiform discharge is that Breach Rhythm consists of sharp or spiky transients that are not followed by a slow-wave component. [3, 7] While increased amplitude, focal asymmetry, and intermixed faster frequencies are all characteristic of Breach Rhythm, the lack of an associated slow wave is the most definitive feature to rule out an epileptiform spike or sharp wave. [3, 6, 7]
Question 3: During a recording of a 25-year-old patient in light sleep, the technologist observes trains of 6-11 Hz arc-shaped (arciform), monophasic waves in the left temporal region. They occur without disrupting the background and are not followed by a slow wave. They sometimes appear as single transients that resemble sharp waves. This pattern is best described as:
- Wicket Spikes (Correct answer)
- Mu Rhythm
- Benign Small Sharp Spikes (BSSS/BETS)
- Lambda Waves
Correct answer: Wicket Spikes
Wicket spikes are defined as 6-11 Hz, arc-shaped (arciform), monophasic waves that occur in the temporal regions, especially during drowsiness and light sleep. [2, 35] They can appear in trains or as single transients, which can be easily mistaken for epileptiform sharp waves, but they lack an after-going slow wave and do not disturb the background activity. [33, 35] Mu rhythm is found over the central region and is related to motor activity. [21, 29] BSSS/BETS are lower in amplitude and shorter in duration. [12] Lambda waves are occipital and occur during wakefulness with visual scanning. [1, 38]
Question 4: A patient is in a coma due to a severe metabolic disturbance. The EEG shows generalized, high-amplitude (>70 µV), periodically repeating waves at 1-2 Hz. Each wave has a distinct morphology: a small initial negative deflection, a large surface-positive sharp wave, and a following slow negative wave. This pattern is most consistent with:
- Frontal Intermittent Rhythmic Delta Activity (FIRDA)
- Generalized Periodic Discharges (GPDs)
- Triphasic Waves (Correct answer)
- Burst-Suppression
Correct answer: Triphasic Waves
The described morphology—a negative-positive-negative sequence with a dominant surface-positive phase, high amplitude, and periodic recurrence at 1-2 Hz—is the classic definition of triphasic waves. [4, 5] This pattern is strongly associated with metabolic encephalopathy, among other conditions causing altered mental status. [16, 31] While they can be considered a subset of GPDs, the specific triphasic morphology is the most precise answer. FIRDA is typically restricted to the frontal regions and lacks this specific three-phase shape. Burst-suppression consists of periods of high-voltage activity alternating with profound attenuation.
Question 5: Which of the following non-epileptiform patterns is characterized by its location over the sensorimotor cortex, a frequency of 8-10 Hz, an arciform or comb-like morphology, and its attenuation with contralateral limb movement or the thought of movement?
- Posterior Dominant Rhythm (Alpha)
- Mu Rhythm (Correct answer)
- Rhythmic Mid-Temporal Theta of Drowsiness (RMTD)
- Lambda Waves
Correct answer: Mu Rhythm
The Mu rhythm is the idling rhythm of the sensorimotor cortex. It is defined by its central location (C3, Cz, C4), alpha-range frequency (typically 8-10 Hz), arc-like shape, and its unique reactivity—it blocks or attenuates with contralateral motor activity, imagined motor activity, or tactile stimulation, but not with eye-opening. [21, 29, 39]
Question 6: Positive Occipital Sharp Transients of Sleep (POSTS) and Lambda waves are two non-epileptiform patterns that share a similar morphology and occipital location. What is the primary distinguishing feature between them?
- The polarity of the sharp component.
- The frequency of the transients.
- The patient's state of consciousness. (Correct answer)
- The symmetry of the waveforms.
Correct answer: The patient's state of consciousness.
The key factor that differentiates POSTS from Lambda waves is the patient's state. Lambda waves occur exclusively during the awake state when the patient's eyes are open and they are visually scanning their environment. [38, 40] In contrast, POSTS are a hallmark of drowsiness and light sleep (N1/N2) and disappear when the patient is awake. [28, 30, 32]
EEG - Electroencephalography Non-Epileptiform Abnormalities Questions and Answers 1
An EEG recording from a 55-year-old patient in a drowsy state shows bilateral, synchronous, rhythmic 5-7 Hz sharply contoured waves over the parietal and posterior temporal regions.
The pattern has an abrupt onset and offset, lasts for approximately 45 seconds, and does not evolve in frequency or morphology.
The patient remains unresponsive to auditory stimuli during the event.
Which of the following non-epileptiform patterns is most likely being observed?