Childhood absence epilepsy (CAE). Petit Mal seizures. Typical absence seizures.
Incidence
Accounts for 5-15% of childhood epilepsies. There is genetic heterogeneity. It is autosomal dominant condition.
Clinical Characteristics
Childhood absence epilepsy (CAE) is a subtype of idiopathic generalized epilepsy and accounts for 5 to 15% of childhood epilepsies. It is considered an epileptic syndrome. Manifestations begin at age 6-7 years, in contrast to juvenile absence epilepsy, which begins around puberty. The main features are frequent absence seizures (several per day) and bilateral, synchronous, symmetric 3-Hz spike waves on EEG. Generalized tonic-clonic seizures (GTCS) often develop during adolescence. Otherwise, absence seizures may either remit or persist into adulthood. A typical absence seizure consists of a sudden loss of awareness. The child will suddenly stop their activities and stare blankly into space. They will be unresponsive to voice. The seizure is sometimes associated with repetitive, purposeless movements of the mouth or eyes (called automatisms), mainly when it last more than 20 seconds. This can include eyelid flickering or fluttering and lip smacking. A seizure usually last between five and 20 seconds and usually stops as suddenly as it starts, with the child resuming their normal activities, with no postictal drowsiness or confusion. Absence seizures tend to happen more commonly when the child is bored, sitting quietly or when they are tired or unwell. Conversely, they happen less often when the child is engaged with an activity that they enjoy. Children with CAE usually develop normally, although uncontrolled absence seizures may impact on the child’s ability to learn at school. Sometimes a child’s concentration or memory is said to be very poor before the diagnosis of the childhood absence epilepsy is made. It has been defined 3 subsyndromes of CAE. The first subsyndrome, which accounts for approximately 40 to 60% of CAE patients, is characterized by absence seizures as the sole phenotype and remits spontaneously during adolescence. The second subsyndrome, which accounts for another 40% of CAE patients, persists into adolescence and adulthood, during which patients develop tonic-clonic seizures. The third subsyndrome accounts for a smaller percentage (possibly 10 to 12%) of CAE patients and is characterized by the development of tonic-clonic and myoclonic seizures during adolescence, after the onset of absences in childhood. Febrile seizures occur in about 3% of children and 10 to 15% of persons with childhood absence epilepsy have febrile seizures before the onset of epilepsy. Febrile convulsions are a common seizure type in relatives of childhood absence epilepsy probands.
Precipitants
Absence seizures tend to happen more commonly when the child is bored, sitting quietly or when they are tired or unwell. Hyperventilation trigger these type of seizures.
Provocation Tests
Hyperventilation (over-breathe) for three to four minutes will trigger an absence seizure in over 90 per cent of children with typical CAE, and is important in making the diagnosis.
Diagnostic Procedures
It is a clinical-EEG diagnosis. The diagnosis is usually suggested by the history. The EEG shows simultaneous bilateral, synchronous, symmetric 3-Hz spike and waves episodes simultaneously with clinical absences.