Approach Considerations
EEG is the centerpiece of the diagnostic evaluation. If neuroimaging is performed, magnetic resonance imaging is preferred. Results are often normal, reflecting a genetic rather than structural etiology, although congenital brain abnormalities sometimes are observed. In some forms of childhood myoclonic epilepsy, progressive cortical atrophy may be seen.
Electroencephalography
The ictal EEG correlate of myoclonic seizures consists of fast spike-wave discharges (>2.5 Hz), which, at times, are associated with slower 2- to 2.5-Hz discharges. [10] Interictal recordings may be normal or show slowing, depending on the etiology. Like other generalized epilepsies, abnormalities are frequently seen on routine EEG, even if myoclonus is not captured.
Brief (< 3 seconds) interictal bursts of irregular polyspike-waves may be seen either spontaneously or with photic stimulation. The occurrence of these discharges is increased during non–rapid eye movement (REM) sleep.
Also see EEG in Common Epilepsy Syndromes, EEG Video Monitoring, and Generalized Epilepsies on EEG.
Additional Testing
Genetic tests
In select cases, testing for SCN1A or other genetic etiologies suggested by clinical history and/or examination may be appropriate.
Lumbar puncture
Lumbar puncture may be helpful in identifying mitochondrial disorders (elevated cerebrospinal fluid [CSF] lactate) or nonketotic hyperglycinemia (elevated CSF glycine). Elevated protein may indicate a neurodegenerative disease.
