EEG - Electroencephalography Activation Procedures Questions and Answers 1 — Questions and Answers
Question 1: The primary physiological mechanism by which hyperventilation (HV) activates epileptiform discharges is through inducing:
- Respiratory acidosis and cerebral vasodilation.
- A decrease in heart rate and systemic blood pressure.
- Respiratory alkalosis and cerebral vasoconstriction. (Correct answer)
- Increased cerebral blood flow and oxygenation.
Correct answer: Respiratory alkalosis and cerebral vasoconstriction.
Hyperventilation causes a rapid decrease in arterial CO2 (hypocapnia), leading to respiratory alkalosis. The brain compensates for this change in blood pH by constricting cerebral blood vessels, which reduces cerebral blood flow and can lead to mild cerebral hypoxia, thereby lowering the seizure threshold in susceptible individuals.
Question 2: During intermittent photic stimulation (IPS) on a 15-year-old patient, the EEG shows bursts of generalized spike-and-wave and polyspike-and-wave discharges that are time-locked to the flash stimulus, outlast the stimulus, and are self-sustaining. This response is best described as a:
- Photomyogenic response.
- Photoparoxysmal response. (Correct answer)
- Photic driving response.
- Lambda wave activation.
Correct answer: Photoparoxysmal response.
A photoparoxysmal response (PPR) is an abnormal, epileptiform response to IPS characterized by spike-and-wave or polyspike-and-wave discharges. These discharges are often generalized, may continue after the stimulus stops, and are clinically significant for photosensitive epilepsies. A photic driving response is a normal occipital rhythm that follows the flash frequency, and a photomyogenic response is a muscle artifact.
Question 3: A 72-year-old patient is referred for a routine EEG. Their medical history includes a recent ischemic stroke one week ago, severe chronic obstructive pulmonary disease (COPD), and sickle cell trait. Which activation procedure is specifically contraindicated for this patient?
- Eye opening and closing.
- Photic stimulation.
- Sleep recording.
- Hyperventilation. (Correct answer)
Correct answer: Hyperventilation.
Hyperventilation is contraindicated in patients with conditions that could be dangerously exacerbated by cerebral vasoconstriction. These include recent stroke or TIA, severe cardiopulmonary disease, sickle cell disease or trait, and Moya Moya disease.
Question 4: Which of the following describes the typical, normal response to hyperventilation in a healthy 8-year-old child's EEG?
- A buildup of generalized, rhythmic, high-amplitude delta and theta slowing. (Correct answer)
- The appearance of generalized 3 Hz spike-and-wave discharges.
- Attenuation of the posterior dominant rhythm with no other changes.
- Development of focal sharp waves over the temporal regions.
Correct answer: A buildup of generalized, rhythmic, high-amplitude delta and theta slowing.
A normal response to HV, especially prominent in children and adolescents, is the development of generalized, often high-amplitude, rhythmic slowing in the delta and theta frequency ranges. This is known as a "buildup" response and should resolve shortly after HV is discontinued. Generalized spike-and-wave or focal sharps would be abnormal findings.
Question 5: The primary reason for obtaining a sleep recording during an EEG is that sleep, particularly non-REM sleep, is a potent activator of:
- Alpha coma patterns.
- Photoparoxysmal responses.
- Interictal epileptiform discharges. (Correct answer)
- Triphasic waves.
Correct answer: Interictal epileptiform discharges.
Drowsiness and non-REM sleep are powerful activators of interictal epileptiform discharges (IEDs). Many patients with epilepsy may have a normal awake EEG but show clear abnormalities only during sleep, which significantly increases the diagnostic yield of the study.
Question 6: When performing intermittent photic stimulation (IPS) according to standard laboratory protocols, what is the most appropriate action for the technologist?
- Instruct the patient to keep their eyes open for the entire duration of the procedure.
- Continue flashing for at least 30 seconds after a generalized discharge appears to confirm its persistence.
- Begin with the highest frequency (30 Hz) and decrease in 5 Hz increments.
- Present flashes at varying frequencies, typically starting low and increasing, testing with both eyes open and eyes closed. (Correct answer)
Correct answer: Present flashes at varying frequencies, typically starting low and increasing, testing with both eyes open and eyes closed.
Standard IPS protocol involves presenting flash trains of several seconds at various frequencies (e.g., 1, 3, 5, 10, 15, 20, 25, 30 Hz). It is critical to test under both eyes-open and eyes-closed conditions, as photosensitivity can vary. The stimulus should be stopped immediately if a clear, self-sustaining epileptiform discharge is triggered to prevent inducing a seizure.
EEG - Electroencephalography Activation Procedures Questions and Answers 1
The primary physiological mechanism by which hyperventilation (HV) activates epileptiform discharges is through inducing: