Cryptogenic late-onset epileptic spasms: an overlooked syndrome of early childhood?

PURPOSE: Few reports detailing late-onset epileptic spasms have been published. To determine whether this condition merely represents a late variant of classic West syndrome or exhibits specific features distinct from the latter and related to a later stage of brain maturation, we analyzed the whole population with this specific seizure type, excluding symptomatic cases to avoid the effect of brain lesion.
METHODS: We reviewed the files of the 56 children evaluated for epileptic spasms in clusters having begun at age 12 months or later and analyzed clinical and video-EEG data of the 22 patients (4-17 years; mean, 8.5 years) without obvious cause.
RESULTS: Interictal EEG did not show classic hypsarrhythmia. A temporal or temporofrontal slow wave and/or spike focus could be identified in all cases. Twelve children showed spasms with a tonic component. Ictal EEG revealed generalized high-voltage slow wave followed by diffuse voltage attenuation with superimposed fast activity. All children also exhibited other types of recorded seizures consisting of bursts of spike-waves with temporofrontal predominance, reminiscent of "atypical absences." In contrast with the occurrence of tonic components within a cluster of spasms, no tonic seizure stricto sensu was recorded or reported by the caregivers. In 10 children, treatment (two vigabatrin, seven hydrocortisone, one adrenocorticotropic hormone) achieved complete cessation of seizures and disappearance of focal EEG anomalies, but spasms persisted in 12 children.
CONCLUSIONS: The cryptogenic group in our series without recognized cause and temporal or temporofrontal EEG anomalies seems to represent a type of epileptic encephalopathy intermediary between West and Lennox-Gastaut syndromes, in terms of seizure types and interictal EEG, and could correspond to dysfunction of the maturation process of the temporal lobe, possibly due to an undisclosed lesion.