Is hypsarrhythmia a form of non-convulsive status epilepticus in infants?

Abstract

The earliest English language description of hypsarrhythmia reported an almost continuous EEG pattern, although later studies showed a degree of state dependence. Its principal features are very high amplitude and irregular slow waves with superimposed multifocal epileptiform discharges. Paroxysms of spasms are clearly overt seizure events, and there are variable EEG patterns associated with this ictus. There remains a debate about the definitional boundaries of hypsarrhythmia, and about the defining characteristics of NCSE. There is evidence that hypsarrhythmia is an age-dependent EEG pattern that evolves, sometimes independently of clinical features. Frequently, hypsarrhythmia is associated with delay in or regression of neuro-developmental skills, and recent studies have reported that a longer lead time to diagnosis and effective treatment is associated with poorer long-term neuro-developmental outcomes. Recent consensus definitions and classifications of NCSE have suggested boundaries that permit inclusion of hypsarrhythmia as an EEG pattern of NCSE. In practice, adopting the idea that hypsarrhythmia is a form of NCSE might lead to earlier appropriate investigation of infants with subtle developmental delay or regression, hence avoiding treatment delays and potentially preserving developmental potential.

Resting-state activity in development and maintenance of normal brain function

“…Although there is no characteristic EEG feature of EE that is most closely associated with clinical disability (43), there is general agreement that early successful medical or surgical treat- ment is associated with improved developmental outcome (44-47); see SI Text for more discussion of this. Thus, EE appears to be injurious, but the mechanism of injury remains uncertain.…”

Nonconvulsive status epilepticus and coma

“…The burst suppression pattern may indicate severe brain dysfunction or a certain level of generalized anesthesia. No valid signs differentiate epileptic burst suppression as it occurs in children with West (Hrachovy & Frost, 2003; Lux, 2007) or Ohtahara syndrome from the patterns found in deep coma and the supposedly nonepileptic patterns found in generalized anesthesia. Because treatment of SE by general anesthesia should be governed by sedation down to burst suppression pattern (Claassen et al., 2001), the question arises of how this can be managed in NCSE characterized by suppression burst pattern itself.…”

Epileptic activity is a surrogate for an underlying etiology and stopping the activity has a limited impact on developmental outcome

“…In the younger child this is best illustrated in infantile spasms with hypsarhythmia; in the older child and teenager the clearest example is ring chromosome 20 syndrome. In both of these situations an individual, who may have been previously developmentally normal, can develop rapid and significant cognitive and behavioral decline in association with epileptic seizures and severe EEG abnormalities including nonconvulsive status epilepticus …”

“…In both of these situations an individual, who may have been previously developmentally normal, can develop rapid and significant cognitive and behavioral decline in association with epileptic seizures and severe EEG abnormalities including nonconvulsive status epilepticus. 2,3 Labeling a group of epilepsies as "the epileptic encephalopathies" paradoxically risks minimizing the impact of epileptic activity on cognition and behavior more widely in epilepsy. The epileptic encephalopathies should not be considered as a specific group of epilepsies, but rather, the concept of epileptic encephalopathy or epilepsy with encephalopathy should be applicable to all types of epilepsy and epilepsy syndromes and used by clinicians whenever it is relevant in the clinical course of a particular individual, at any age.…”