Severe Neonatal Epilepsy with Suppression-Burst Pattern (Early Epileptic Encephalopathy); Erratic Myoclonus. A 5-day-old boy born full term without complications who presented with hypotonia, apnea, irritability, and jitteriness. He was found to have frequent erratic myoclonus and myoclonic seizures. MRI was unremarkable. EEG shows suppression-burst (S-B) pattern and subclinical electrographic focal seizures (not shown). It also shows no significant changes during erratic myoclonus (open arrow). An extensive metabolic work-up was negative.
There are two severe neonatal epilepsies with S-B pattern, Ohtahara syndrome (OS) and early myoclonic encephalopathy (EME). The EEG shows bursts, lasting several seconds, of polyspikes alternating with very low-voltage activity, this combination being called “suppression bursts.” The S-B pattern may be asymmetric, affecting mainly the side of the cortical malformation, hemimegalencephaly, focal cortical dysplasia, Aicardi syndrome, olivary-dentate dysplasia, or schizencephaly.1–3 The onset of seizures in OS is within the first 2–3 months but most commonly within the first 10 days. The main type of seizure in OS is the tonic spasm. Myoclonic seizures and erratic myoclonus are rare. A majority of cases of OS are associated with structural brain abnormalities, including porencephaly, hydrocephalus, hemimegalencephaly, and lissencephaly. No familial case of OS have been reported.
EME is characterized by an early onset in the neonatal period with the main seizure types of erratic and massive myoclonus and partial seizures. The most common cause of EME is metabolic disease.
The causes of OS are symptomatic or organic; the causes of EME can be genetic, metabolic, or entirely unknown. OS causes tonic spasms and partial seizures. EME causes myoclonic and partial seizures. The EEG of OS contains periodic S-B and is irrespective of waking and sleeping, while EME may have S-B only during sleep. OS commonly transitions to West syndrome. EME transition to West syndrome is transient, if there is any transition at all. The EEG course of S-B in OS is that they turn into hypsarrhythmia in 3–6 months. The EME S-B course is long lasting.4,5 However, the distinction between these two conditions may be difficult because brief spasms are difficult to distinguish from myoclonus. The distinction between S-B and hypsarrhythmia with extreme fragmentation in sleep also is difficult in many cases because in OS, the S-B evolves into the more continuous asynchronous spike- and slow-wave activity of hypsarrhythmia.3