EEG - Electroencephalography Non-Epileptiform Abnormalities 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?

Accepted Answer

Subclinical Rhythmic Electrographic Discharge of Adults (SREDA)

Answer

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?

Accepted Answer

The absence of an after-going slow wave.

Answer

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:

Accepted Answer

Wicket Spikes

Answer

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:

Accepted Answer

Triphasic Waves

Answer

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?

Accepted Answer

Mu Rhythm

Answer

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]

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Non-Epileptiform Abnormalities Questions and Answers