Prevalence
Very small; <0.5 to 1% among selected patients with epileptic disorders.

Age at onset
5 months to 13 years (median 7 years).

Sex
Males (70%) predominate.

Neurological and mental state
1/3 of patients are normal (idiopathic form). The others are symptomatic, with mainly learning difficulties prior to seizures.

Etiology
20% have a family history of epilepsy. Myoclonic absences (the seizures, not the syndrome) are due to idiopathic, cryptogenic, or symptomatic causes, including chromosomal abnormalities.

Clinical manifestations
Myoclonic absences are the defining symptom. They manifest with rhythmic myoclonic jerks mainly of the shoulders, arms, and legs with a concomitant tonic contraction. The jerks may be unilateral or asymmetrical. Eyelid twitching is practically absent but perioral myoclonias are frequent. Impairment of consciousness varies from mild to severe. Myoclonic absences last 8 to 60 sec and often occur many times per day.

Generalized tonic-clonic seizures or atonic seizures occur in 2/3 of patients, predicting an unfavorable prognosis (these are probably symptomatic cases). Absence status epilepticus is rare.

Seizure-precipitating factors
Nearly invariably provoked by hyperventilation.

Inter-ictal EEG
Usually normal background at onset but may deteriorate later or be abnormal in symptomatic cases. Brief generalized, focal, or multifocal spikes and slow waves appear in 50% of patients.

Ictal EEG
Generalized 3 Hz spike/multiple spike slow-wave discharges, even in those with unilateral or asymmetrical clinical manifestations. Each myoclonic jerk coincides with the spike component of the discharge.

Prognosis
Myoclonic absences are often resistant to treatment. Half of patients (probably of symptomatic cause) continue having seizures in adult life, developing features of other types of epilepsy such as Lennox-Gastaut syndrome or juvenile myoclonic epilepsy. Half of those who were normal prior to the onset of absences develop cognitive and behavioral impairment.

Differential diagnosis
Mainly between idiopathic and symptomatic cases that manifest with the same seizure type (myoclonic absences).

Management options*
Early control of absences may secure normal development. High doses of valproate are used, often with lamotrigine or ethosuximide, levetiracetam or clonazepam.

*Expert opinion, please check FDA-approved indications and prescribing information

See also: http://professionals.epilepsy.com/page/syndromes_myoclonicabsences.html

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