Stare into space, unresponsive for around 10 seconds
Afterwards just carry on unaware anything has happened – or possibly very brief confusion (seconds)
Clue that not just day dreaming is that most also have clonic movements, minor changes in tone (eg head drops, or held object dropped), automatisms (repetitive movements of eyes, mouth).
No myoclonus (else likely to be juvenile myoclonic epilepsy). Some get generalised tonic-clonic seizures in adolescence but these are infrequent and respond well to treatment.
Usually when sat quietly rather than actively engaged in something. Precipitated by sleep deprivation, as other epilepsies, but also hyperventilation (90% detected after 3 minutes – get them to count aloud)
Atypical would be gradual onset, last longer, have more obvious changes in tone – but continuum
Most genetic. GLUT1 (glucose transporter protein type 1, coded for by SLC2A1 gene, involved in glucose transfer across blood-brain barrier) mutations are present in up to 10% of early childhood absence epilepsy (ie under 5yrs). Heterozygous mutations are mostly de novo but may be inherited as AD trait. SLC2A1 positive often not helped by valproate and ethosuximide, whereas ketogenic diet often effective.
EEG shows sudden onset 3Hz spike and wave, esp with photic stimulation/hyperventilation. Interictal is often normal. Clinically apparent if more than 3 seconds of activity, but detailed neuropsych assessment suggests that non-clinical absences do cause functional impairment. Atypical have slower spike waves and rarely have normal interictal.
60-80% full remission, usually during puberty; in most cases, absences disappear on monotherapy but there are resistant cases (unpredictable, other than SLC2A mutations).