Childhood Absence Epilepsy – CAE – Classical Absence Seizures
Symptoms, Diagnosis, Prognosis, Genetics, and Treatment of Childhood Absence Epilepsy – Absence Triggers – EEG Findings
Childhood Absence Epilepsy (CAE)
Childhood Absence Epilepsy is one of the most common epilepsy syndromes of the childhood.
Frequent absence seizures in an otherwise healthy child is a hallmark of CAE.
Other types of seizures are uncommon in classical childhood absence epilepsy.
The prognosis is favorable, since the vast majority of children are seizure free by puberty.
Epidemiology and Genetics of CAE
Childhood Absence Epilepsy comprises 10% to 12% of all childhood epilepsies. CAE is 2 to 5 times more common in girls.
The symptoms appear between the ages of 4 and 10 with median age of 6 years.
First degree relatives of patients with CAE have 17% chance of developing this syndrome. About half of children have first or second degree relatives with seizures and 20% have history of febrile seizures. Identical twins of children with CAE have 75% chance of developing the disorder.
Multiple genes encoding for proteins responsible for electrolytes transport across nerve cells membranes appear to be involved: magnesium transporter, calcium and chloride channels, and GABA receptors.
Symptoms of Childhood Absence Epilepsy
The main symptom is hundreds or thousands of typical absence seizures per day. Absences have abrupt onset and abrupt termination. Duration of absences is from 4 to 20 seconds with 10 seconds on average.
During the absence, there is a profound impairment of consciousness. Any voluntary activity is interrupted for the time of the absence. Response to the environment is lacking.
There is no loss of body tone or falls.
The majority of children are either partially or completely unaware of the absence seizure. For this reason, this type of seizure may stay unnoticed for prolonged period of time and the symptoms are attributed to daydreaming and spacing out.
Staring, with eyes wide open, is very typical (78% of absence seizures).
Absences are predictably precipitated by hyperventilation. Flashing light does not trigger this type of seizures.
Automatisms (automatic purposeless movements) are present in two thirds of absence seizures, lip smacking is most common. Myoclonic eyelid movements (3 Hz per second) are also typical.
Myoclonus (brief muscle contractions) in the rest of the face and body or more complex automatic behavior makes childhood absence epilepsy unlikely. Loss of muscle tone, falls, gradual onset of los of awareness and recovery, as well as absences lasting longer than 20 seconds are the signs of some other epilepsy syndrome.
Generalized Tonic-clonic Seizures
A small percentage of children have occasional GTCS. Generalized tonic-clonic seizures in CAE do not occur until puberty; absences usually remit by this time. It is a subject of debate if GTCS actually happen in childhood absence epilepsy. It all depends on how strict the diagnostic criteria were used in the diagnosis.
Cognitive and Psychiatric Abnormalities in CAE
There are no obvious cognitive abnormalities but neuropsychological testing reveals attention and problem solving issues.
The chances of anxiety disorder, depression, social isolation, and ADHD are significantly higher than in the general population.
Diagnosis of Childhood Absence Epilepsy
The diagnosis is made on the basis of typical clinical picture: numerous typical absences with appropriate age of onset.
Presence of other types of seizures, incomplete or gradual onset and termination of loss of consciousness, too early or too late onset of seizures, atypical EEG, or other neurological or developmental problems are consistent with different types of epileptic syndromes.
Electroencephalogram outside absence seizures has normal background. Occipital slow wave activity is noted in 20 percent. Occasional generalized of focal spike wave are not uncommon.
During the seizure, there are generalized 3 Hz spike-and-wave discharges (from 1 to 3 spikes per wave). The frequency may vary from 2.5 to 5 Hz. The onset and termination of abnormal activity are abrupt. Recording of an absence is not hard task in CAE, considering a high frequency of seizures. Hyperventilation, sleep deprivation, and drowsiness are strong triggers of absence seizures and they are typically used in association with EEG recording.
Treatment of Childhood Absence Epilepsy
Ethosuximide is the drug of choice in childhood absence epilepsy. Ethosuxemide allows achieving a complete control of seizures in half of the children. It is generally well tolerated. Most common side effects are nausea, vomiting, hyperactivity, drowsiness, and insomnia. Ethosuxemide has no effect on generalized tonic-clonic seizures.
Valproate is slightly superior to Ethosuxemide. It also controls GTCS. Valproate is tolerated worse and it has less favorable side effect profile.
Lamotrigine is less effective than Ethosuxemide but it is tolerated the best. Resistant cases sometimes require combination with Valproate. Lamotrigine has a severe skin reaction (Steven-Johnson Syndrome) as a potential side effect, which can be precipitated by a combination with Valproate.
Topiramate and Acetazolamide may be tried in resistant cases.
Carbamazepine, Gabapentin, Vigabatrin, and Tiagabine are contraindicated because they may aggravate absence seizures.
Phenytoin and Phenobarbital have no effect on absence epilepsy.
Prognosis in CAE
The prognosis largely depends on the diagnostic criteria used in a particular child. The majority of children with typical CAE respond well to medications and will be seizure free by puberty.
An average duration of this epilepsy syndrome is from 4 to 10 years.
A small percentage will develop occasional generalized tonic-clonic seizures which are sometimes carried into adulthood.
Frequently associated mood disorders and attention deficit disorder will have their own courses irrelevantly of the epileptic symptoms.
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