Myoclonus - Practical Approach All Myoclonus are not Epileptic


Dr PAM Kunju, Trivandrum    15 January 2018

  1. Myoclonus is a sudden, shock-like contraction of a muscle or group of muscles.
  2. Myoclonus can be divided into cortical, subcortical, spinal or peripheral, based on the presumed source of its generation.
  3. Based on etiology, myoclonus may be classified as epileptic or nonepileptic (physiological, essential, or psychogenic).
  4. It is caused by abrupt muscle contraction, in the case of positive myoclonus, or by sudden cessation of ongoing muscular activity, in the case of negative myoclonus (NM). NM results from toxic-metabolic causes.
  5. In a given patient, more than one form of myoclonus may occur. For instance, in posthypoxic myoclonus (Lance–Adams syndrome), cortical myoclonus may coexist with brainstem myoclonus.
  6. Cortical myoclonus mainly affects the distal upper limbs and face. It can be stimulus sensitive, typically to touch. If prolonged, it is called as epilepsia partialis continua.
  7. Subcortical myoclonus originates between the cortex and the spinal cord and is divided into nonsegmental and segmental types. Nonsegmental subcortical myoclonus – Startle/hyperekplexia and reticular reflex myoclonus.
  8. Brainstem myoclonus is manifested by generalized jerks and its most striking clinical feature is sensitivity to auditory stimuli. Two main types are (i) startle response, which may be physiologic or pathologic (hyperekplexia), and (ii) reticular reflex myoclonus.
  9. Segmental subcortical myoclonus e.g., palatal myoclonus – caused by a lesion in the Guillain–Mollaret triangle – (dentate nucleus, red nucleus and inferior olivary nucleus).
  10. Spinal segmental myoclonus is usually symptomatic of an underlying structural lesion such as syringomyelia, myelitis, spinal cord trauma, vascular lesion or malignancy.
  11. Epileptic myoclonus is accompanied by generalized epileptiform discharges on EEG, but the myoclonus itself may be focal, segmental or generalized.
  12. Generalized myoclonus can occur in the syndromes of primary (idiopathic) generalized epilepsy (e.g. juvenile myoclonic epilepsy) or in the secondary (symptomatic) generalized epilepsies (e.g., progressive myoclonic epilepsy [PME]).
  13. Focal myoclonus can occur in symptomatic epilepsy, in the setting of infection, inflammation, vascular disease, trauma or tumors.
  14. Among PMEs, slow myoclonus is a feature of SSPE. In addition to myoclonus, PMEs have dementia and cerebellar ataxia.
  15. Early infantile myoclonic epilepsies can be benign depending on age (neonatal, infantile or childhood). Early infantile epileptic encephalopathies (EIEE) are characterized by myoclonus and other types of seizures and EEG feature called as suppression burst pattern.
  16. The treatment of myoclonus depends on the underlying disorder.
  17. Antiepileptic drugs such as valproate, levetiracetam and piracetam are effective in cortical myoclonus. Clonazepam may be helpful in all types of myoclonus.

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