What is the appropriate evaluation and treatment for an infant presenting with myoclonus?

Myoclonus in Infancy: Evaluation and Management

Initial Diagnostic Approach

The most critical first step is to distinguish benign myoclonus of early infancy (BMEI) from epileptic conditions, particularly infantile spasms (West's syndrome), through careful clinical characterization and EEG confirmation, as BMEI requires no treatment and has an excellent prognosis. 1

Key Clinical Features to Identify

Benign Myoclonus of Early Infancy (BMEI):

• Myoclonic jerks of the head and/or upper limbs occurring in clusters, typically mimicking infantile spasms 1
• Consciousness is preserved during attacks 1, 2
• Episodes usually occur during wakefulness, more rarely during sleep or drowsiness 1
• Onset occurs in the first year of life, mainly between 4 and 7 months of age 1
• Attacks have abrupt onset, last a few seconds, but multiple episodes per day often occur 1
• Frequently triggered by excitement, frustration, postural changes, or sensory stimuli 1, 2
• Attacks usually cease by age 2 years 1

Essential Diagnostic Workup

EEG is mandatory to confirm the diagnosis:

• Ictal EEG must be normal to confirm BMEI diagnosis 1
• Interictal EEG must also be normal 1
• Video EEG monitoring during episodes is recommended to capture events and confirm absence of epileptiform activity 3
• Neurological status and development must be normal 1

Critical Differential Diagnoses to Exclude

West's Syndrome (Infantile Spasms):

• Distinguished by abnormal EEG with hypsarrhythmia and poor prognosis 3
• Requires immediate antiepileptic treatment, unlike BMEI 3

Hyperekplexia:

• Excessive startle response to sudden noise or touch, present from birth or evident prenatally in last trimester 1
• Prolonged stiffening in neonates and young infants following startle 1

Sandifer Syndrome:

• Paroxysms of head tilt after eating, secondary to gastroesophageal reflux 1

Benign Paroxysmal Torticollis:

• Recurrent episodes of abnormal, painless head postures alternating from side to side 1
• Onset usually before 3 months of age 1
• Episodes may last from minutes to several days 1

Transient Dystonia of Infancy:

• Paroxysmal episodes of abnormal upper limb posture with occasional trunk and single lower limb involvement 1
• Onset typically between 5 and 10 months 1
• Resolves between 3 months and 5 years 1

Treatment Recommendations

For Benign Myoclonus of Early Infancy

No antiepileptic treatment is indicated for BMEI 3

• Reassurance and observation are the only interventions needed 3
• Complete resolution occurs spontaneously within 2 weeks to 8 months of onset 3
• All children have normal neurologic development 3
• Care must be taken to avoid unnecessary and potentially harmful antiepileptic therapy 3

For Epileptic Myoclonus (If Diagnosed)

If EEG confirms epileptic myoclonus, levetiracetam is first-line treatment:

• For myoclonic seizures in patients ≥12 years with juvenile myoclonic epilepsy: initiate at 1000 mg/day (500 mg BID), increase by 1000 mg/day every 2 weeks to recommended dose of 3000 mg/day 4
• For pediatric patients ages 4-16 years with partial onset seizures: initiate at 20 mg/kg/day in 2 divided doses (10 mg/kg BID), increase every 2 weeks by 20 mg/kg increments to recommended dose of 60 mg/kg/day (30 mg/kg BID) 4
• Alternative first-line agents include sodium valproate or clonazepam 5, 6

Common Pitfalls to Avoid

Misdiagnosis of BMEI as West's syndrome:

• This leads to unnecessary antiepileptic drug exposure with potential adverse effects 3
• Always obtain EEG confirmation before initiating treatment 3

Premature neuroimaging:

• In typical BMEI with normal neurological examination and development, neuroimaging is not indicated 1
• Reserve imaging for atypical features, abnormal neurological examination, or developmental concerns 1

Failure to document episodes:

• Video recording by parents can be invaluable for diagnosis 3
• Video EEG monitoring captures both clinical and electrographic features simultaneously 3