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MS – Paroxysmal Tonic Spasms — SCE Neurology MCQ

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HardMultiple Sclerosis & CNS InflammationMS – Paroxysmal Tonic SpasmsSCE Neurology

A 50-year-old man with known MS presents with episodic tonic spasms — brief (10–30 second), painful, unilateral tonic posturing of the right arm occurring multiple times daily, sometimes triggered by movement. MRI shows a demyelinating lesion in the left posterior limb of the internal capsule. What is the underlying mechanism and what is the treatment?

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Correct answer: C — Paroxysmal tonic spasms due to ephaptic transmission in demyelinated axons — carbamazepine or oxcarbazepine

Paroxysmal tonic spasms in MS are brief, stereotyped, painful tonic posturing episodes caused by ephaptic (cross-talk) transmission between adjacent demyelinated axons, particularly in the internal capsule or spinal cord. They are not true epileptic seizures (EEG is normal during events) but respond well to sodium channel blockers (carbamazepine, oxcarbazepine). They are a recognised MS symptom. A: These are not epileptic seizures (no EEG correlate). C: These are not simple muscle cramps. D: The mechanism is ephaptic, not dystonic. E: This is not spasticity.

Reference: NICE NG100 MS (2022); ABN MS Guidelines (2022)