Could an infant's episodes of myoclonus be something other than a seizure, such as benign neonatal sleep myoclonus?

Can Infant Myoclonus Be Non-Epileptic?

Yes, benign neonatal sleep myoclonus is a common non-epileptic cause of myoclonic movements in infants that is frequently misdiagnosed as seizures and should never be treated with antiepileptic drugs. 1, 2

Key Distinguishing Features of Benign Neonatal Sleep Myoclonus

Diagnostic Criteria

Benign neonatal sleep myoclonus is definitively diagnosed by five essential features that distinguish it from epileptic seizures:

• Myoclonic jerks occur exclusively during sleep - the movements stop abruptly and consistently when the infant is aroused or awakened 1, 2, 3
• Normal EEG during events - no paroxysmal or epileptiform activity accompanies the myoclonus, which is the critical distinguishing feature from seizures 1, 2, 3
• Neonatal onset - symptoms begin within days to a few weeks of birth, typically within the first 16 days (median 3 days) 1, 4
• Self-limited course - myoclonus resolves spontaneously within 3-10 months (median 2 months) without treatment 1, 4
• Excellent neurological outcome - all affected infants have consistently favorable developmental outcomes 1, 2

Clinical Presentation Variations

The semiology is more varied than traditionally described:

• Bilateral synchronous movements are most common, but lateralized myoclonus affecting one side can occur 1, 4
• Duration varies from brief seconds to prolonged episodes exceeding 30 minutes, which can mimic status epilepticus 1, 5
• Sleep stage specificity - movements typically occur during drowsiness or early non-REM sleep, though some infants have events throughout different sleep stages 4
• Facial involvement is absent - the myoclonus never involves facial muscles, which helps distinguish it from epileptic seizures 4
• Paradoxical worsening with restraint - gentle restraint often increases the amplitude and frequency of movements 2

Critical Management Principles

What NOT to Do

Antiepileptic drugs are contraindicated and harmful - infants with benign neonatal sleep myoclonus should never receive antiepileptic treatment, as these medications do not help and may worsen the myoclonus 1, 2

• In documented cases, myoclonus actually worsened despite anticonvulsant therapy and decreased substantially when treatment was stopped 2
• The condition is self-limited and requires no pharmacologic intervention 1

Diagnostic Workup

When evaluating suspected benign neonatal sleep myoclonus:

• Video-EEG monitoring during events is essential - this definitively excludes epileptic seizures by demonstrating normal EEG activity during myoclonic jerks 1, 2, 3
• Neurological examination should be performed but is typically normal or shows only mild hyperexcitability 4
• Neuroimaging is not routinely indicated unless other concerning features suggest structural pathology 4

Distinguishing from True Neonatal Seizures

When to Suspect Actual Seizures

The following features suggest true epileptic seizures rather than benign sleep myoclonus:

• Movements persist during wakefulness - true seizures do not stop consistently with arousal 6, 2
• Abnormal EEG correlates - epileptic seizures show excessive synchronous cortical electrical activity 6
• Associated neurological abnormalities - seizures often present with additional symptoms like altered consciousness, hemiparesis, or apnea 6
• Specific high-risk contexts - hypoxic-ischemic encephalopathy (46-65% of neonatal seizures), intracranial hemorrhage, stroke, or metabolic derangements suggest true seizures 6, 7

Timing Considerations

• Hypoxic-ischemic seizures occur within the first 2 days of life in 90% of cases 6, 7
• Benign sleep myoclonus typically begins within the first 16 days but can start slightly later 4
• Infectious causes are more likely beyond the seventh day of life 7

Common Pitfalls

Misdiagnosis is Extremely Common

• Primary care physicians rarely consider benign sleep myoclonus - in one series, none of the referring physicians made this diagnosis initially 1
• The movements can mimic convulsive status epilepticus - prolonged episodes with high amplitude jerking are frequently mistaken for serial seizures 2, 5
• Family history may be present - some infants have relatives with nocturnal myoclonus, tic disorders, or sleep disturbances, suggesting genetic factors 5

Key to Avoiding Misdiagnosis

Always perform video-EEG monitoring when the clinical diagnosis is uncertain - the absence of epileptiform activity during recorded myoclonic events definitively establishes the benign nature of the condition and prevents unnecessary antiepileptic drug exposure 1, 2, 3