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