EEG Activation Procedures 4 — Questions and Answers
Question 1: Which patient condition is an absolute contraindication to photic stimulation during EEG?
- Drowsiness
- History of photosensitive epilepsy with prior status epilepticus (Correct answer)
- Mild hypertension
- Anxiety disorder
Correct answer: History of photosensitive epilepsy with prior status epilepticus
History of photosensitive epilepsy with prior status epilepticus is an absolute contraindication because photic stimulation could trigger a prolonged seizure.
Question 2: What EEG response is termed 'photoparoxysmal' during intermittent photic stimulation?
- Posterior dominant rhythm attenuation
- Generalized spike-and-wave or polyspike-and-wave discharges time-locked to flashes (Correct answer)
- Focal theta slowing over the occipital region
- Increased beta activity frontally
Correct answer: Generalized spike-and-wave or polyspike-and-wave discharges time-locked to flashes
A photoparoxysmal response consists of generalized epileptiform discharges (spike-wave or polyspike-wave) that are provoked by and time-locked to photic stimulation.
Question 3: During hyperventilation, if the patient has an underlying brain tumor, you would most likely expect to see:
- Bilateral synchronous generalized slowing
- Focal or lateralized slow-wave abnormality that increases in prominence (Correct answer)
- High-frequency gamma activity over the tumor site
- Suppression of all EEG activity
Correct answer: Focal or lateralized slow-wave abnormality that increases in prominence
Focal structural lesions such as tumors typically produce focal or lateralized slow-wave abnormalities that are accentuated by hyperventilation-induced hypocapnia.
Question 4: The standard recommended duration of the hyperventilation activation procedure in adults is:
- 1 minute
- 2 minutes
- 3 minutes (Correct answer)
- 5 minutes
Correct answer: 3 minutes
ACNS guidelines recommend 3 minutes of hyperventilation followed by at least 1 minute of post-HV recording to capture delayed responses.
Question 5: A technologist notices the patient begins breathing very slowly and shallowly during hyperventilation. The best action is to:
- Stop the test immediately and call a physician
- Verbally coach the patient to breathe more deeply and consistently (Correct answer)
- Increase the flash rate on the photic stimulator simultaneously
- Document it and continue without intervention
Correct answer: Verbally coach the patient to breathe more deeply and consistently
Verbal coaching helps the patient maintain adequate depth and rate of breathing to achieve the desired hypocapnic effect.
Question 6: Which of the following flash frequencies used in intermittent photic stimulation (IPS) is most likely to elicit a photoparoxysmal response in photosensitive individuals?
- 1–2 Hz
- 3–5 Hz
- 15–20 Hz (Correct answer)
- 50 Hz
Correct answer: 15–20 Hz
Frequencies between approximately 15–20 Hz are the most common range for provoking photoparoxysmal responses in photosensitive patients.
Question 7: What is the physiological mechanism by which hyperventilation activates epileptiform activity?
- Hypercapnia causes cerebral vasodilation and increased ICP
- Hypocapnia causes cerebral vasoconstriction, reducing cerebral blood flow and causing neuronal hyperexcitability (Correct answer)
- Increased oxygen delivery stabilizes neuronal membranes
- Respiratory alkalosis suppresses inhibitory interneurons permanently
Correct answer: Hypocapnia causes cerebral vasoconstriction, reducing cerebral blood flow and causing neuronal hyperexcitability
Hyperventilation lowers CO2 (hypocapnia), causing cerebral vasoconstriction, reduced perfusion, and subsequent neuronal hyperexcitability that can provoke epileptiform discharges.
EEG Activation Procedures 4
Which patient condition is an absolute contraindication to photic stimulation during EEG?