Are early myoclonic encephalopathy (EME) and the Ohtahara syndrome (EIEE) independent of each other?

BACKGROUND: Early myoclonic encephalopathy (EME) and the Ohtahara syndrome are currently listed as two separate syndromes in the classification of epilepsies. The most prominent differentiating points are the observations that patients with Ohtahara syndrome experience predominantly tonic seizures; their seizures evolve to infantile spasms and the prognosis is often worse than patients with EME.

SUMMARY POINTS: We performed a literature review of published cases. Although syndromes may have distinct courses, the differentiation early on may be impossible as both myoclonus and tonic seizures may coexist. There is also an overlap in the etiologies. Tonic seizures are considered a manifestation of brainstem dysfunction and it is possible that this is more prominent in Ohtahara syndrome. To date, there are 17 autopsy cases (12 presumed to be Ohtahara cases and 5 EME). Evidence of hindbrain pathology was present in all. Tonic seizures or tonic posturing was a feature of all cases. We suggest that the two syndromes may represent a continuum and that the prominence of tonic seizures in the Ohtahara syndrome may be an indication of brainstem dysfunction which may play an important role in the subsequent transition to infantile spasms.