~3% of adults with seizures, ~10% of all idiopathic generalized epilepsies (IGEs) in adults.

Age at onset
Generalized tonic-clonic seizures (GTCS) usually appear in adult life (18 to 40 years), although onset of absences is undetermined.

Males = females.

Neurological and mental state

Probably genetically determined.

Clinical manifestations
Phantom absences are so mild that they are inconspicuous to the patient and imperceptible to the observer. On video-EEG, they manifest with interruption, delays, or errors of breath counting and occasionally with eyelid blinking.

Generalized tonic-clonic seizures (GTCS) are usually the first overt clinical manifestation. These are of late onset (adult life), infrequent, and without consistent circadian distribution or specific precipitating factors.

Half of patients suffer from absence status epilepticus of many hours alone or prior to GTCS.

Seizure-precipitating factors
Absences are nearly invariably provoked by hyperventilation.

Inter-ictal EEG
Normal background but often with focal paroxysmal abnormalities of localized slow, sharp waves or spikes or both, occurring either independently or in association with generalized discharges. EEG photosensitivity is exceptional.

Ictal EEG
Brief (3 to 4 sec) generalized discharges of 3 to 4 Hz spike/multiple spike waves.

May be a lifelong propensity to seizures of undetermined onset and remission. Phantom absences, although frequent, do not appear to affect daily activity. IGE with phantom absences is usually easily controlled with appropriate AEDs.

Differential diagnosis
The main problems to consider are that phantom absences usually evade clinical detection, GTCS are of late onset, and absence status epilepticus is often misdiagnosed as complex focal seizures or prodrome to GTCS.

Management options*
There may be many people in the general population with phantom absences but without GTCS. For those who will eventually have GTCS, treatment may be needed (valproate or lamotrigine).

Absence status epilepticus, for which most patients are aware, should be terminated with self-administered benzodiazepines.

Contraindicated drugs include vigabatrin#, tiagabine, carbamazepine, and gabapentin.

*Expert opinion, please check FDA-approved indications and prescribing information
#Not approved by the FDA

This page was adapted from:

The educational kit on epilepsies: The epileptic syndromes By C. P. Panayiotopoulos Originally published by MEDICINAE 21 Cave Street, Oxford OX4 1BA
First published 2006 and reprinted in 2007

Authored By: 
C. P. Panayiotopoulos MD, PhD, FRCP
Authored Date: 
Reviewed By: 
Steven C. Schachter MD
Sunday, June 1, 2008