EEG - Electroencephalography Activation Procedures Questions and Answers

Question 1

The primary physiological mechanism by which hyperventilation (HV) activates epileptiform discharges is through inducing:

Accepted Answer

Respiratory alkalosis and cerebral vasoconstriction.

Answer

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:

Accepted Answer

Photoparoxysmal response.

Answer

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?

Accepted Answer

Hyperventilation.

Answer

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?

Accepted Answer

A buildup of generalized, rhythmic, high-amplitude delta and theta slowing.

Answer

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:

Accepted Answer

Interictal epileptiform discharges.

Answer

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.

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Practice Test

EEG - Electroencephalography Activation Procedures Questions and Answers