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EEG – Normal Hyperventilation Response — SCE Neurology MCQ

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HardClinical NeurophysiologyEEG – Normal Hyperventilation ResponseSCE Neurology

During a routine EEG, hyperventilation produces several transient patterns in different epochs. Which finding is most consistent with a physiological hyperventilation response rather than an epileptiform or focal pathological abnormality?

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Correct answer: A — Bilaterally synchronous high-amplitude slowing without spikes that resolves shortly after hyperventilation stops

Hyperventilation causes hypocapnia and reduced cerebral blood flow and may produce a bilaterally synchronous build-up of high-amplitude slow activity, especially in younger people. In the absence of spikes, evolution or a persistent focal abnormality, prompt resolution after hyperventilation supports a physiological activation response rather than epilepsy. Generalised 3-Hz spike-and-wave with behavioural arrest is an electroclinical absence seizure. Evolving temporal rhythmic activity suggests an ictal pattern, persistent unilateral delta suggests focal dysfunction, and a photoparoxysmal response belongs to photic rather than hyperventilation activation.

Reference: ANS/BSCN Guidelines for Hyperventilation During EEG Recordings: https://www.bscn.org.uk/data/files/Guidelines/Hypervent.pdf; EEG characteristics during hyperventilation: https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2021.727297/full