Myoclonus is defined as sudden, brief, shocklike involuntary contractions of a single muscle or muscle group. These jerks can be isolated or repetitive, rhythmic or arrhythmic, symmetrical or asymmetrical, synchronous or asynchronous, generalized or focal. Myoclonus may be physiologic (e.g., hypnic jerks before sleep, startle responses), pharmacologic, or pathologic, often associated with neurologic disorders such as epilepsy, encephalopathies, or neurodegenerative diseases. It may also precede seizures, making early recognition vital for patient safety and appropriate management.

Pathophysiology

Myoclonic jerks arise from abnormal hyperexcitability of neurons within the central nervous system (CNS), which may involve:

1. Cortical mechanisms: Sudden discharges in the motor cortex produce focal or generalized myoclonus.

2. Subcortical or brainstem mechanisms: Disinhibition of reticular or subcortical motor pathways triggers generalized or segmental jerks.

3. Spinal mechanisms: Hyperexcitable spinal interneurons lead to segmental myoclonus.

4. Metabolic or toxic encephalopathy: Accumulation of neurotoxins (e.g., uremia, hepatic failure) alters neuronal excitability.

5. Post-hypoxic injury: Neuronal damage after hypoxia can trigger intention myoclonus or generalized jerks during recovery.

Stimuli such as bright lights, sudden sounds, or unexpected touch can precipitate jerks in susceptible individuals.

Emergency interventions

• Assess seizure activity and ensure airway patency.

• Monitor vital signs for arrhythmias or respiratory compromise.

• Seizure precautions:

  • Gently position patient on the floor or bed.

  • Place a pillow or rolled towel under the head to prevent injury.

  • Loosen tight clothing, particularly around the neck.

  • Turn the head to the side to reduce risk of aspiration.

• Keep resuscitation equipment readily available.

History and Physical Examination

• Determine frequency, severity, location, and triggers of myoclonus.

• Ask about preceding or associated seizures.

• Evaluate for sensory stimulus-induced myoclonus.

• Assess level of consciousness (LOC) and cognitive status.

• Examine for muscle rigidity, wasting, and deep tendon reflexes.

• Identify any neurologic deficits or systemic symptoms indicating underlying disease.

Medical Causes

Special considerations

• Implement fall precautions: pad side rails, remove hazards, supervise ambulation.

• Seizure precautions: keep oral airway and suction equipment at bedside.

• Administer antimyoclonic drugs as indicated: ethosuximide, L-5-hydroxytryptophan, phenobarbital, clonazepam, carbidopa.

• EEG and other neurologic evaluations may be required to confirm diagnosis and monitor progression.

Patient counseling

• Educate about safety measures, avoiding triggers, and seizure precautions.

• Advise family involvement for supervision and support.

• Refer to neurology or community resources for chronic or progressive cases.

Pediatric pointers

• Myoclonus is uncommon but may occur in children with:

  • Subacute sclerosing panencephalitis

  • Severe meningitis

  • Progressive poliodystrophy

  • Childhood myoclonic epilepsy

  • Encephalopathies (e.g., Reye’s syndrome)

Early recognition is critical to prevent complications and guide therapy.