EEG Ambulatory 4 — Questions and Answers
Question 1: When a patient on ambulatory EEG reports a suspected seizure event via the event button but the recording shows no ictal activity, the MOST likely explanation is:
- Equipment malfunction caused signal dropout
- The event was a non-epileptic psychogenic episode (Correct answer)
- The button was pressed too late after the event ended
- Electrode impedance was too high during the event
Correct answer: The event was a non-epileptic psychogenic episode
Non-epileptic psychogenic events (PNES) are a common finding when patient-reported events lack EEG correlate during ambulatory monitoring.
Question 2: A 24-hour ambulatory EEG uses a sample rate of 256 Hz. What is the highest frequency that can be faithfully represented according to the Nyquist theorem?
- 256 Hz
- 512 Hz
- 128 Hz (Correct answer)
- 64 Hz
Correct answer: 128 Hz
The Nyquist theorem states the maximum representable frequency is half the sampling rate, so 256 Hz ÷ 2 = 128 Hz.
Question 3: Which of the following activities is MOST likely to produce muscle artifact that obscures the EEG during an ambulatory recording?
- Sleeping in a supine position
- Reading a book while seated
- Chewing food during a meal (Correct answer)
- Writing in a patient diary
Correct answer: Chewing food during a meal
Chewing activates the temporalis and masseter muscles, generating high-amplitude EMG artifact that directly overlies temporal EEG electrodes.
Question 4: A patient's ambulatory EEG diary notes 'episode of deja vu lasting 30 seconds' at 14:22. The technologist reviewing the recording should FIRST:
- Mark the entire day as artifactual
- Navigate to 14:22 and review the corresponding EEG channel data (Correct answer)
- Discard the recording due to subjective symptom reporting
- Re-apply electrodes before reviewing
Correct answer: Navigate to 14:22 and review the corresponding EEG channel data
The technologist should correlate the diary timestamp with the EEG data at that exact time to look for ictal or interictal changes.
Question 5: During ambulatory EEG review, runs of rhythmic 4–7 Hz theta activity appearing symmetrically during an afternoon recording segment are MOST consistent with:
- Absence seizures
- Normal drowsiness (Correct answer)
- Temporal lobe epilepsy
- Electrode pop artifact
Correct answer: Normal drowsiness
Symmetric theta slowing during daytime hours is a normal finding associated with drowsiness or light sleep stage N1.
Question 6: A common challenge unique to ambulatory EEG compared to in-lab recording is:
- Inability to record delta frequencies
- Lack of patient diary correlation
- Increased susceptibility to movement and environmental artifacts (Correct answer)
- Requirement for general anesthesia
Correct answer: Increased susceptibility to movement and environmental artifacts
Ambulatory recordings are highly susceptible to movement artifact, cable sway, and environmental electrical interference because the patient moves freely in daily life.
Question 7: When reviewing an ambulatory EEG, the technologist notices that channels Fp1 and Fp2 show high-amplitude slow waves every 3–4 seconds throughout the entire recording. The MOST likely cause is:
- Frontal lobe epilepsy
- Electrode gel drying causing increased impedance artifact
- Blink artifact from the frontopolar electrode location (Correct answer)
- Delta slowing from a frontal mass lesion
Correct answer: Blink artifact from the frontopolar electrode location
Blink artifact consistently appears at Fp1 and Fp2 as large slow deflections due to the corneoretinal dipole movement directly beneath these frontopolar electrodes.
EEG Ambulatory 4
When a patient on ambulatory EEG reports a suspected seizure event via the event button but the recording shows no ictal activity, the MOST likely explanation is: