HISTORICAL NOTE

Childhood absence epilepsy is a well-established entity defined by its clear clinical features and characteristic EEG. Not until the 1950s did clinicains become aware of a distinct juvenile absence syndrome (Janz and Christian 1957). The International League Against Epilepsy, in 1989, classified juvenile absence epilepsy under "idiopathic generalized epilepsies and syndromes with age-related onset" (Commission on Classification and Terminology of the International League Against Epilepsy 1989).


CLINICAL MANIFESTATIONS

Juvenile absence epilepsy develops insidiously in physically and mentally healthy adolescents. Age at onset is usually between 10 and 17 years, with a peak between 10 and 12 years (Wolf 1992). In contrast to a female preponderance in childhood absence epilepsy, males and females are affected equally in juvenile absence epilepsy (Commission on Classification and Terminology of the International League Against Epilepsy 1989). Because the frequency of the absences is low, and the symptoms are relatively trivial, the disorder may go unnoticed until generalized tonic-clonic seizures appear.

The semiology of the absences in this syndrome is not significantly different from those seen in childhood absence epilepsy. Differences in duration of the absence and in the extent of disturbance of consciousness stated by Panayiotopoulos and colleagues are based on too few cases to be considered as established (Panayiotopoulos et al 1989). In contrast to childhood absences, which usually occur daily, juvenile absences are much more sporadic. Therefore, juvenile absences have been described as "spanioleptic" (spanios meaning scanty or scarce in Greek). The incidence of generalized tonic-clonic seizures (more than three quarter of patients) seems to be higher in juvenile absence epilepsy than in childhood absence epilepsy. This may be due to nondetection of patients with absences only. In approximately one third of cases, generalized tonic-clonic seizures appear as the initial seizure type before the onset of absences. Most generalized tonic-clonic seizures in this syndrome occur upon awaking. Only a small number of patients experience seizures either during sleep or randomly (Wolf and Inoue 1984). Myoclonic seizures associated with juvenile absence epilepsy occur in a minority of cases (Wolf and Inoue 1984).


CLINICAL VIGNETTE

No information is available.


ETIOLOGY

Juvenile absence epilepsy is an idiopathic epilepsy, and approximately 11% of patients reveal a family history of epilepsy (Wolf 1992). There appears to be a genetic relationship among juvenile absence epilepsy, childhood absence epilepsy, juvenile myoclonic epilepsy, and epilepsy with grand mal seizures on awaking, since more than one of these phenotypes of idiopathic generalized epilepsy can appear in the same family (Delgado-Escueta et al 1990).


BIOLOGICAL BASIS

The fundamental mechanisms of juvenile absence epilepsy are unknown; however, animal models of absence seizures suggest that rhythmic thalamic projections to diffusely epileptogenic cortex produce the characteristic hypersynchronous discharges and that enhanced inhibitory, as well as excitatory, mechanisms are involved (Gloor and Fariello 1988). Intracellular recordings from cortical neurons during experimentally induced absences in the cat have shown that the EEG spike reflects excitatory membrane events and that the slow wave reflects GABA-mediated inhibition (Giaretta et al 1987). These findings confirm an old hypothesis of Jung and Tšnnies (Jung and Tšnnies 1950). Various genetic conditions with absences have been described in mice. They differ both in phenotype and causative genetic aberration (Noebels 1995).


EPIDEMIOLOGY

The incidence and prevalence of juvenile absence epilepsy in the general population are not known. In a survey of 7332 patients from 14 epilepsy centres in Lombardy (Osservatore Regionale per l'Epilessia Lombardy 1996), 1494 (17.4%) had some kind of idiopathic generalized epilepsy, and 160 of these were diagnosed as having juvenile absence epilepsy.


PREVENTION

Early detection and treatment of patients with absences can be a means of secondary prevention of convulsive seizures.


DIFFERENTIAL DIAGNOSIS

Onset in adolescence and frequency of absences distinguish this disorder from the childhood form of absence epilepsy. In epilepsy with grand mal seizures on awaking generalized convulsions are the presenting feature of the disorder, whereas in juvenile myoclonic epilepsy, bilateral myoclonic seizures are the most prominent symptom. There is, however, some overlap between juvenile absence epilepsy and the two last-mentioned syndromes, and the assignation of a patient to one or the other may be to some extent arbitrary. Complex partial seizures of temporal lobe origin can occasionally mimick absences but are as a rule longer in duration, and there are usually some focal features clinically or in the EEG.


DIAGNOSTIC WORKUP

In juvenile absence epilepsy, the ictal and interictal EEG is characterized by symmetrical, generalized spike-wave discharges most prominent in the frontal region. Their frequency can be faster (3.5 Hz to 4.5 Hz) than in typical childhood absence epilepsy (3 Hz to 3.5 Hz). The EEG paroxysms are precipitated by sleep deprivation and by hyperventilation, less commonly by photic stimulation. A video EEG with tests of responsiveness during a spike-wave discharge may be required to ascertain whether a patient has absences or only subclinical spikes and waves. Neurologic examination and neuroimaging results are normal.


PROGNOSIS

The response to therapy is good. Approximately 82% of cases will become seizure-free with the traditional anti-absence drugs such as succinimides and valproate (Wolf and Inoue 1984). With the advent of lamotrigine this figure should have improved. Factors associated with suboptimal control include absences with mild clonic components, more than 10 generalized tonic-clonic seizures, generalized tonic-clonic seizures during sleep and at random, history of absence status, developmental delay, mental retardation, spike-wave bursts of more than 5 seconds, asymmetry of spike-waves, persistance of absences beyond age 25, and persistance of absences for more than 12 years (Wolf and Inoue 1984). An attempt at meta-analysis of reports on the outcome of absence epilepsy was undertaken. Juvenile absence epilepsy was not seperated from other absence epilepsies, and a high variation of results was noted (Bouma et al 1996).


MANAGEMENT

Traditionally, absences were successfully treated in most cases by ethosuximide, valproate, or a combination of both. Valproate is appropriate monotherapy if generalized tonic-clonic seizures or myoclonic jerks or both are also part of the clinical presentation. Lamotrigine is now an additional option and is considered especially in female patients of childbearing age because of the increased teratogenic risk with valproate.


PREGNANCY

Although no information is available that is specific to this syndrome and pregnancy, information is available on epilepsy and pregnancy.


ANESTHESIA

No syndrome-specific information is available.


REFERENCES CITED

Bouma PAD, Westendorp RGJ, van Dijk JG, Peters ACB, Brouwer OF. The outcome of absence epilepsy: A meta-analysis. Neurology 1996; 47:802-8.

Commission on Classification and Terminology of the International League Against Epilepsy. Proposal for revised classification of epilepsies and epileptic syndromes. Epilepsia 1989;30:389-99.

Delgado-Escueta AV, Greenberg D, Weissbecker K, Liu A, Treiman L, Sparkes R, Park MS, Barbetti A, Terasaki PI. Gene mapping in the idiopathic generalized epilepsies: juvenile myoclonic epilepsy, childhood absence epilepsy, epilepsy with grand mal seizures, and early childhood myoclonic epilepsy. Epilepsia 1990;31(Suppl 3):S19-29.

Giaretta D, Avoli M, Gloor P. Intracellular recordings in pericruciate neurons during spike and wave discharges of feline generalized penicillin epilepsy. Brain Res 1987;405:68-79.

Gloor P, Fariello RG. Generalized epilepsy: some of its cellular mechanisms differ from those of focal epilepsy. Trends Neurosci 1988;11:63-8. Janz D, Christian W. Impulsiv-Petit mal. J Neurol 1957;176:346-86.

Jung R, Tšnnies JF. Hirnelektrische Untersuchungen Ÿber Entstehung und Erhaltung von Krampfentladungen. Die VorgŠnge am Reizort und die BremsfŠhigkeit des Gehirns. Arch Psychiat Nervenkr 1950; 185:701.

Noebels JL. Genetic mechanisms of spike-wave epilepsies in mouse mutants. In: Duncan JS, Panayiotopoulos CP, editors. Typical absences and related epileptic syndromes. London: Churchill Livingstone, 1995:29-38.

Osservatore Regionale per l'Epilessia Lombardy. ILAE classification of epilepsies: its applicability and practical value of different diagnostic categories. Epilepsia 1996;37:1051-9.

Panayiotopoulos CP, Obeid T, Waheed G. Differentiation of typical absences in epileptic syndromes. A video EEG study of 224 seizures in 20 patients. Brain 1989; 112: 1039-56.

Wolf P, Inoue Y. Therapeutic response of absence seizures in patients of an epilepsy clinic for adolescents and adults. J Neurol 1984;231:225-9.

Wolf P. Juvenile absence epilepsy. In: Roger J, Bureau M, Dravet C, Dreifuss FE, Perret A, Wolf P, editors. Epileptic syndromes in infancy, childhood and adolescence. 2nd ed. London: John Libbey, 1992:307-12.

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