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Myoclonus

For further information, see CMDT Part 24-14: Movement Disorders

Key Features

  • Myoclonic jerks are sudden, shock-like muscle contractions

  • Occasional myoclonic jerks may occur in anyone, especially when drifting into sleep

  • General or multifocal myoclonus: common in patients with idiopathic epilepsy and certain hereditary disorders

  • Generalized myoclonic jerking may

    • Accompany uremic and metabolic encephalopathies

    • Result from therapy with levodopa or tricyclic antidepressants

    • Occur in alcohol or drug withdrawal states

    • Follow anoxic brain damage

  • It is common in subacute sclerosing panencephalitis and Creutzfeldt-Jakob disease

Clinical Findings

  • Myoclonus can be focal or generalized and can occur spontaneously or in response to certain stimuli (eg, noise)

Diagnosis

  • Clinical diagnosis

  • Electroencephalography is often helpful in clarifying an epileptic basis, and CT or MRI scan may reveal the causal lesion

Treatment

  • Myoclonus may respond to

    • Anticonvulsant drugs, especially valproic acid or levetiracetam

    • Benzodiazepines, particularly clonazepam (Table 24–2)

    • Piracetam (up to 16.8 g daily; not available in United States)

  • Myoclonus after anoxic brain damage may respond to

    • Clonazepam (sometimes)

    • Oxitriptan (often), given in gradually increasing doses up to 1.0–1.5 mg daily

  • In patients with segmental myoclonus, a localized lesion (spinal or cerebral) should be searched for and treated appropriately

Table 24–2.Medication treatment for seizures in adults (in alphabetical order within classes).
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Table 24–2. Medication treatment for seizures in adults (in alphabetical order within classes).
Medication Usual Adult Daily Oral Dose Minimum No. of Daily Doses Time to Steady-State Medication Levels Optimal Medication Level and Laboratory Monitoring1 Selected Side Effects and Idiosyncratic Reactions
Generalized or Focal Seizures
Brivaracetam2,3 50–100 mg 2 1–2 days CBC, liver biochemical tests Somnolence, fatigue, ataxia, vertigo, psychosis, leukopenia, hypersensitivity (bronchospasm and angioedema).
Cannabidiol4 5–20 mg/kg 2 11–13 days Liver biochemical tests at baseline, 1, 3, and 6 months

Somnolence, fatigue, anorexia, weight loss, anemia, diarrhea, rash, sleep disorder, infections.

Elevation in liver enzymes may occur; reduce dose in hepatic impairment.
Carbamazepine2,3,5,6 400–1600 mg (immediate- or extended-release) 2 3–4 days

4–8 mcg/mL

CBC, liver biochemical tests, BUN/Cr

Nystagmus, dysarthria, diplopia, ataxia, drowsiness, nausea, blood dyscrasias, hepatotoxicity, hyponatremia, Stevens-Johnson syndrome.7

May exacerbate myoclonic seizures.
Cenobamate2,3 200–400 mg 1 14 days Liver biochemical tests, potassium Multiorgan hypersensitivity, QT shortening, somnolence, dizziness, cognitive dysfunction, blurred vision.
Clobazam8 10–40 mg 2 7–10 days   Lethargy and somnolence, ataxia, insomnia, dysarthria, aggression, constipation, fever, Stevens-Johnson syndrome.
Clorazepate3 22.5–90 mg 2 10 days   Sedation, dizziness, confusion, ataxia, depression, dependency/abuse.
Eslicarbazepine2,3 400–1200 mg 1 4 days Serum sodium and chloride; liver biochemical tests As for carbamazepine.
Ezogabine3 300–1200 mg 3 2–3 days ECG to assess QT interval Dizziness, somnolence, confusion, vertigo, nausea, ataxia, psychiatric disturbances, prolonged QT interval, retinal abnormalities.9
Felbamate2,3,8,10 1200–3600 mg 3 4–5 days CBC and ...

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