Myoclonus

Myoclonus, as a symptom of movement disorders:

Diagnosis:
  • Clinical: Rapid, brief, involuntary, jerk, muscle contraction (positive myoclonus) or inhibition of tone (negative myoclonus)
  • Myoclonus by EMG: bursts <75 msec is diagnostic
Types of myoclonus:

By location:

  • Cortical
  • Subcortical:
    • Brain stem (e.g. opsolonus myoclonus syndrome, hemifacial spasm)
    • Spinal
    • Segmental

By relation to action:

  • Action
  • Postural
  • Reflex

Causes of myoclonus:

Primary:

  • Benign myoclonus (a normal finding, including hiccups)
  • Sleep myoclonus
  • Essential myoclonus
  • Part of idiopathic generalized epilepsy e.g. Juvenile myoclonic epilepsy

Secondary:

  • Systemic conditions:
    • Uremia (renal failure)
    • Liver failure
    • Posthypoxic myoclonus (usually action myoclonus if after recovery, or myoclonic status epilepticus acutely post anoxia)
    • Drug overdose/poisoning
  • Neurodegenerative conditions:
    • Creutzfeldt-Jakob disease
    • Frontotemporal dementia
    • Alzheimer’s disease, Parkinson’s disease, Multiple sclerosis
  • Pure movement disorder:
    • Palatal myoclonus
  • Progressive myoclonus epilepsy (PME), a group of conditions: (see under separate list)
Orthostatic myoclonus:

EMG:

  • Myoclonus= irregular, short duration (less than 100 msec) muscle bursts in the legs
  • +Myoclonus occurring in leg muscles upon standing and not present in the sitting position
  • Or +a marked increase of myoclonic bursting frequency in leg muscles upon standing
  • Also +no myoclonus at rest +non-rhythmic discharges
Negative myoclonus:

EMG: silence

Investigations to consider in patients with myoclonus, on a case by cases basis:
  • Basic metabolic profile creatinine: renal failure,
  • LFTs: liver failure
  • ABG: CO retention
  • EEG: epilepsy e.g. IGE, also CJD, SSPE,
  • Tests for CJD, vCJD
  • Tests for opsoclonus-myoclonus syndrome
  • Tests for SSPE
  • Test for West nile virus WNV
  • Tests for DYT11
  • Tests for Neuronal ceroid lipofuscinosis
  • Tests for Lafora disease
  • MRI: for anoxic brain injury, neuroblastoma, Cerebellopontine angle tumours in hemifacial spasm
Treatment of myoclonus:

If myoclonus is part of an epilepsy syndrome, then treat the myoclonus.
If part of another disease, treat the underlying disease
If due to a mass lesion or compressive lesion, treat the underlying lesion
Midbrain myoclonus:

  • Medications to consider include: Clonazepam. Serotoninergic drugs: clomipramine, fluoxetine.

If localised:

  • Consider botulinum toxin injection
  • Consider above drugs

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