Synopsis
Describe positive and negative myoclonus accurately, distinguish epileptic from physiological, toxic-metabolic and structural causes, identify encephalopathic emergencies, and choose cause-directed or syndrome-specific treatment with neurophysiological support.
- Myoclonus is a sudden, brief, shock-like movement caused either by active muscle contraction—positive myoclonus—or a momentary interruption of tonic muscle activity—negative myoclonus.
- Classify distribution as focal, segmental, multifocal or generalised and relationship to action, posture, stimulus, sleep and awareness before naming a cause.
- Physiological myoclonus includes hypnic jerks and hiccups; symptoms become pathological when persistent, progressive, functionally disruptive or linked to epilepsy or systemic illness.
Key red flags
Brief irregular lapses of sustained posture causing flapping hands, knee buckling or dropping objects suggest asterixis or another negative-myoclonus syndrome.
Investigation priorities
Define distribution, stimulus sensitivity, action relationship and drug or withdrawal exposure.
Management branches
Jerks begin abruptly with confusion, physiological deterioration or a new medicine exposure.
- 1. Stabilise ABCDE, check glucose, temperature and oxygenation, identify convulsive or non-convulsive status and assess for serotonin or neuroleptic malignant syndromes.
- 2. Review prescriptions, renal clearance, dose changes, substances and withdrawal, withholding plausible culprits safely while antidotal or supportive advice is sought.
Key medicines
Levetiracetam for myoclonic seizuresA common adult regimen begins at 250–500 mg twice daily and is titrated to response, with maintenance reduced for renal impairment under BNF and epilepsy-specialist guidance.
Sodium valproate for myoclonic seizuresUse an individualised divided regimen titrated to the lowest effective dose only when current MHRA initiation, specialist and reproductive-risk conditions are satisfied.