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MS Paroxysmal Symptoms – Ephaptic Mechanism Confirmed — SCE Neurology MCQ

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ModerateMultiple Sclerosis & CNS InflammationMS Paroxysmal Symptoms – Ephaptic Mechanism ConfirmedSCE Neurology

A 45-year-old woman with MS develops painful tonic spasms — brief episodes of painful unilateral arm stiffening lasting 10–20 seconds, occurring multiple times daily, triggered by movement or hyperventilation. Her neurologist starts carbamazepine 100 mg BD. Within 48 hours the spasms resolve completely. What does the dramatic response to low-dose carbamazepine suggest about the mechanism?

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Correct answer: A — The response confirms ephaptic transmission — spontaneous impulses spreading between adjacent demyelinated axons, which is abolished by sodium channel blockade at much lower doses than needed for epilepsy

The dramatic response of MS paroxysmal symptoms (tonic spasms, trigeminal neuralgia, dysarthria-ataxia) to low-dose carbamazepine (much lower than anticonvulsant doses) confirms that the mechanism is ephaptic transmission — electrical cross-talk between adjacent demyelinated axons — rather than true epileptic seizure activity. Sodium channel blockers stabilise the demyelinated membrane and prevent this cross-talk. EEG during these events shows no epileptiform activity. A: No EEG correlate — not epileptic. C: Consistent dramatic responses are not placebo. D: Carbamazepine at anticonvulsant doses does not primarily treat spasticity. E: The mechanism is central, not peripheral.

Reference: NICE NG100 MS; ABN MS Guidelines