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Startle Epilepsy – CHRNA4 — SCE Neurology MCQ

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HardEpilepsy & Seizure DisordersStartle Epilepsy – CHRNA4SCE Neurology

A 40-year-old man presents with episodic events of sudden bilateral leg stiffness causing him to fall, without loss of consciousness. The events last 2–5 seconds and occur when he is startled by noise. He has mild cognitive impairment. His mother had epilepsy. Genetic testing shows a mutation in the CHRNA4 gene. What is the most likely diagnosis?

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Correct answer: E — Startle epilepsy

Startle epilepsy is a rare reflex epilepsy where seizures (typically tonic or tonic-clonic) are triggered by unexpected stimuli, most commonly auditory. It is often associated with cortical dysplasia or symptomatic frontal lobe epilepsy. CHRNA4 (nicotinic acetylcholine receptor alpha-4 subunit) mutations are associated with autosomal dominant sleep-related hypermotor epilepsy (SHE, formerly ADNFLE), which can include startle-triggered seizures. B: SHE primarily has nocturnal hypermotor seizures. C: Hyperekplexia has an exaggerated startle response without seizure but is caused by glycine receptor (GLRA1) mutations. D: Cataplexy causes muscle weakness, not stiffness. E: Drop attacks do not have an epileptic mechanism.

Reference: NICE NG217; ILAE Reflex Epilepsies