EEG Activation Procedures 2 — Questions and Answers
Question 1: During hyperventilation activation in EEG, what is the expected normal response in an adult?
- Focal beta activity increase
- Generalized slowing that resolves within 1-2 minutes after cessation (Correct answer)
- Persistent asymmetric delta activity
- Appearance of sleep spindles
Correct answer: Generalized slowing that resolves within 1-2 minutes after cessation
Normal hyperventilation response in adults produces bilateral, symmetrical, generalized slowing (buildup) that resolves within 1-2 minutes of stopping. Persistent or asymmetric slowing is abnormal.
Hyperventilation (HV) causes hypocapnia and cerebral vasoconstriction, producing generalized high-amplitude delta slowing known as the 'buildup response.' In normal adults, this resolves within 1-2 minutes after HV ends. Children and young adults show more prominent buildup. Persistent slowing beyond 2-3 minutes or asymmetric slowing suggests underlying pathology. HV is particularly effective at provoking absence seizures with 3 Hz spike-and-wave. It is contraindicated in patients with moyamoya disease, recent stroke, or sickle cell disease.
Question 2: Photic stimulation at what flash frequency range is most likely to provoke a photoparoxysmal response in susceptible individuals?
- 1-3 Hz
- 15-20 Hz (Correct answer)
- 30-40 Hz
- 50-60 Hz
Correct answer: 15-20 Hz
The photoparoxysmal response, characterized by generalized spike-and-wave or polyspike-and-wave discharges, is most commonly elicited at flash frequencies between 15-20 Hz.
Intermittent photic stimulation (IPS) uses a strobe light at frequencies typically ranging from 1 to 60 Hz. The photoparoxysmal response (PPR) is an abnormal generalized epileptiform response most commonly triggered at 15-20 Hz, though it can occur across a range. Type 4 PPR (generalized spike-and-wave outlasting the stimulus) is the most clinically significant. Photic driving — a normal occipital response at the stimulus frequency — should not be confused with PPR. IPS is an important activation procedure in generalized epilepsies, especially juvenile myoclonic epilepsy.
Question 3: Which of the following is a contraindication for performing hyperventilation during an EEG?
- History of febrile seizures
- Age over 40 years
- Recent cerebrovascular accident (Correct answer)
- History of generalized tonic-clonic seizures
Correct answer: Recent cerebrovascular accident
Recent stroke is a contraindication for hyperventilation because the resulting hypocapnia and cerebral vasoconstriction could worsen ischemia in vulnerable brain tissue.
Hyperventilation causes hypocapnia leading to cerebral vasoconstriction and reduced blood flow. This is dangerous in patients with recent cerebrovascular accidents, severe cardiovascular disease, moyamoya disease, sickle cell disease, or significant pulmonary disease. Advanced age alone is not a strict contraindication, though the buildup response is typically less prominent. A history of seizures is actually an indication, as HV is used to provoke absence seizures diagnostically.
Question 4: What is the recommended duration for hyperventilation during a routine EEG recording?
- 30 seconds
- 1 minute
- 3 minutes (Correct answer)
- 10 minutes
Correct answer: 3 minutes
Standard hyperventilation is performed for 3 minutes with continued recording for at least 1-2 minutes afterward to capture the recovery phase and any provoked abnormalities.
The American Clinical Neurophysiology Society (ACNS) recommends hyperventilation for 3 minutes during routine EEG. The patient breathes deeply at approximately 20 breaths per minute. Recording should continue for at least 1-2 minutes after cessation to capture the resolution of buildup and any late-appearing abnormalities. Some labs extend to 5 minutes if absence seizures are suspected and no abnormality has appeared. The technologist should document the quality of the patient's effort, as poor effort yields unreliable results.
Question 5: What EEG finding during photic stimulation represents a normal physiological response?
- Generalized spike-and-wave complexes
- Photoparoxysmal response
- Photic driving response in occipital regions (Correct answer)
- Frontal intermittent rhythmic delta activity
Correct answer: Photic driving response in occipital regions
Photic driving is a normal response where occipital rhythms entrain to the flash frequency. It represents normal visual cortex reactivity and should not be confused with pathological photoparoxysmal responses.
Photic driving is the entrainment of occipital EEG activity to the frequency (or harmonics/subharmonics) of intermittent photic stimulation. It is a normal physiological response reflecting the integrity of the visual cortex. It is typically symmetric and most prominent at frequencies near the patient's dominant posterior rhythm. Asymmetric photic driving may suggest a structural lesion. In contrast, photoparoxysmal responses involve generalized spike-and-wave activity and are abnormal, suggesting photosensitive epilepsy.
Question 6: Sleep deprivation before an EEG is primarily used to:
- Reduce muscle artifact throughout the recording
- Increase the likelihood of recording epileptiform discharges (Correct answer)
- Improve electrode impedance
- Shorten the overall recording time
Correct answer: Increase the likelihood of recording epileptiform discharges
Sleep deprivation is an activation procedure that increases the yield of detecting epileptiform abnormalities by promoting drowsiness and sleep, states in which interictal discharges are more likely to appear.
Sleep deprivation (typically staying awake the night before) is an important activation procedure that increases the diagnostic yield of EEG by 20-40%. Epileptiform discharges are more common during drowsiness and NREM sleep, particularly during transitions. Sleep deprivation facilitates recording of these states during a routine EEG. Additionally, sleep deprivation itself may lower the seizure threshold. It is especially useful when a standard awake EEG is normal but clinical suspicion of epilepsy remains high. The patient is usually asked to stay awake for 24 hours or sleep only 4 hours.
EEG Activation Procedures 2
During hyperventilation activation in EEG, what is the expected normal response in an adult?