Outcome of children with hyperventilation-induced high-amplitude rhythmic slow activity with altered awareness.

Hyperventilation-induced high-amplitude rhythmic slow activity with altered awareness (HIHARS) is increasingly being identified in children and is thought to be an age-related non-epileptic electrographic phenomenon. We retrospectively investigated the clinical outcome in 15 children (six males, nine females) with HIHARS (mean age 7y, SD 1y 11mo; range 4y 6mo-11y). The presenting feature in 11 cases was blank spells - two of these children also had generalized tonic-clonic seizures (GTCS) - and in one individual the main concern was deteriorating school performance. Three children had symptoms suggestive of focal motor seizures. Of the nine children presenting solely with blank spells, further follow-up (mean duration 18mo, SD 21mo) revealed full resolution of symptoms in six, but three had persistent symptoms. In our study, the symptoms of children with HIHARS presenting with blank spells in isolation appeared to resolve spontaneously and did not evolve into convulsive seizures or other paroxysmal events considered to be clearly epileptic. Children (with HIHARS) who presented with clinical features suggestive of GTCS or focal motor seizures (with or without blank spells) and/or had epileptiform discharges on interictal electroencephalography were subsequently diagnosed with epilepsy. © The Authors. Developmental Medicine & Child Neurology