Childhood Myoclonus: Clinical Entities and Management
Yes, childhood myoclonus exists as several distinct clinical entities, including benign myoclonus of early infancy, juvenile myoclonic epilepsy, and myoclonic seizures associated with various epileptic syndromes. Myoclonus in children can present as both epileptic and non-epileptic phenomena, with important implications for diagnosis, treatment, and prognosis.
Types of Childhood Myoclonus
Epileptic Myoclonus
- Juvenile Myoclonic Epilepsy (JME): Occurs in children 12 years and older, characterized by myoclonic jerks, particularly in the morning 1
- Benign Myoclonic Epilepsy of Infancy: Affects infants aged 4 months to 3 years with brief myoclonic attacks involving mainly the head and upper limbs 2
- Myoclonic seizures in other epileptic syndromes: Can occur in various childhood epileptic conditions including:
- Primary generalized epilepsy
- Lennox-Gastaut syndrome
- Infantile spasms 3
Non-Epileptic Myoclonus
- Benign Myoclonus of Early Infancy: A non-epileptic condition characterized by spasms that resemble West's syndrome but with normal EEG and excellent prognosis 4
- Essential Myoclonus: Can present in childhood with oscillatory movements at 6-8 Hz frequency, sometimes associated with anxiety disorders 5
Diagnostic Features
Clinical Presentation
- Myoclonic jerks are sudden, brief, shock-like involuntary movements caused by muscle contractions or inhibitions 6
- In children with epilepsy, myoclonic movements may be more frequent at onset compared to adults 6
- Myoclonus must be distinguished from:
- Epileptic spasms
- Tonic seizures
- Tics
- Tremor
- Chorea 7
Diagnostic Evaluation
- EEG is essential: Determines if myoclonus has an epileptiform correlate 8
- Epileptic myoclonus is associated with spike or polyspike-wave discharges
- Non-epileptic myoclonus shows normal EEG during episodes 4
- Video EEG monitoring: Particularly important to differentiate benign myoclonus from epileptic conditions 4
Treatment Approaches
Pharmacological Management
- Levetiracetam: Particularly effective for myoclonic seizures in juvenile myoclonic epilepsy, with studies showing 60.4% of patients achieving ≥50% reduction in myoclonic seizure days 1
- Valproate: First-line treatment for benign myoclonic epilepsy of infancy 2
- Clonazepam: Effective for subcortical and brainstem myoclonus 8
- Medications to avoid:
Treatment Considerations
- Non-epileptic myoclonus (such as benign myoclonus of early infancy) should not be treated with anticonvulsants 4
- Polytherapy with a combination of drugs is often needed for complete control of epileptic myoclonus 8
- Early treatment of benign myoclonic epilepsy of infancy is associated with good psychomotor development 2
Prognosis
- Benign Myoclonus of Early Infancy: Excellent prognosis with complete resolution within weeks to months without treatment 4
- Benign Myoclonic Epilepsy of Infancy: Good psychomotor development with early valproate treatment 2
- Juvenile Myoclonic Epilepsy: Generally responds well to appropriate anticonvulsant therapy 1
- Status myoclonus: Continuous myoclonus lasting >30 minutes has poorer prognosis, especially in post-anoxic settings 8
Important Clinical Pearls
- Misdiagnosis is common - benign myoclonus of early infancy is frequently mistaken for West's syndrome, leading to unnecessary anticonvulsant treatment 4
- EEG is crucial for differentiating epileptic from non-epileptic myoclonus in children 3
- Family history of epilepsy or febrile convulsions is present in approximately 30% of cases of benign myoclonic epilepsy in infancy 2
- Photosensitivity is present in about one-third of patients with benign myoclonic epilepsy of infancy 2
Understanding the specific type of childhood myoclonus is essential for appropriate management and avoiding unnecessary treatments that could potentially be harmful, particularly in benign non-epileptic variants.