Is myoclonus characterized by sudden, brief, and lightning-like jerks of a specific muscle, group of muscles, or the entire body?

Myoclonus: Characteristics and Definition

Yes, myoclonus is correctly characterized by sudden, brief, and lightning-like jerks of a specific muscle, group of muscles, or even the entire body. 1

Clinical Features of Myoclonus

• Myoclonus presents as brief, involuntary jerks caused by muscular contractions (positive myoclonus) or sudden cessation of ongoing muscular activity (negative myoclonus) 2
• These movements are typically very brief, lasting only 10-50 milliseconds 3
• Myoclonic jerks can affect a single muscle, a group of muscles, or can be generalized, involving the entire body 1, 4
• Consciousness is preserved during myoclonic episodes, distinguishing it from some epileptic events 5

Types and Classification

• Myoclonus can be classified based on:

  • Clinical presentation (physiological, essential, epileptic, or symptomatic) 4
  • Anatomical source (cortical, subcortical, spinal, or peripheral) 2
  • Distribution (focal, segmental, multifocal, or generalized) 6

• Benign myoclonus of early infancy (BMEI) is characterized by myoclonic jerks of the head and/or upper limbs, usually occurring in clusters and mimicking infantile spasms 5

Differentiating Myoclonus from Other Movement Disorders

• Myoclonus differs from tics, which are also brief jerks but typically have a more complex pattern and can be temporarily suppressed 5
• Myoclonus should be distinguished from convulsive syncope, where movements occur after loss of consciousness rather than being the primary symptom 5
• Unlike dystonia, which involves sustained muscle contractions, myoclonus is characterized by brief, shock-like movements 2
• Hyperekplexia can mimic myoclonus but is specifically triggered by sudden noise or touch and includes an excessive startle response 5

Common Causes and Triggers

• Symptomatic myoclonus can result from:

  • Post-hypoxic brain injury 4
  • Toxic-metabolic disorders 4
  • Medication side effects 4
  • Neurodegenerative diseases 7
  • Epileptic syndromes 3

• Triggers may include:

  • Excitement or frustration 5
  • Postural changes 5
  • Sensory stimuli 5
  • Specific movements (in kinesigenic forms) 5

Diagnostic Approach

• Electrophysiological tests are crucial for determining whether myoclonus is cortical, subcortical, or spinal in origin 2
• EEG recording during episodes can help identify awareness, reactivity, and potential epileptic correlates 1
• The pattern of myoclonus (at rest, during posture maintenance, or with action) provides important diagnostic clues 2

Treatment Considerations

• Treatment often requires multiple medications for acceptable results 6
• Antiepileptic drugs like valproate, levetiracetam, and piracetam are particularly effective for cortical myoclonus 2
• Levetiracetam has demonstrated effectiveness in treating myoclonic seizures in juvenile myoclonic epilepsy, with 60.4% of patients showing significant improvement compared to 23.7% with placebo 8
• Clonazepam may be helpful across various types of myoclonus 2
• Focal and segmental myoclonus may benefit from botulinum toxin injections 2

Clinical Pearls and Pitfalls

• Myoclonus can be confused with seizures, but preservation of consciousness during episodes is an important distinguishing feature 5
• When myoclonus is small and repetitive, it may be difficult to distinguish from tremor without neurophysiological testing 7
• Status myoclonus starting within 48 hours after cardiac arrest is associated with poor neurological outcomes, though some patients can recover 1
• Treatment response varies significantly based on the underlying cause and physiological classification of the myoclonus 2