HISTORICAL NOTE AND NOMENCLATURE

The first reports concerning absence seizures with severe clonic or myoclonic jerks appeared in 1966 (Gibberd 1966). Only a few years later, however, myoclonic absences were recognized as a specific seizure type (Tassinari et al 1969) and proposed as the essential feature of a distinct syndrome (Tassinari and Bureau 1985).

The 1989 revised international classification of epilepsies and epileptic syndromes placed this syndrome under "cryptogenic or symptomatic generalized epilepsies and syndromes" (Commission on Classification and Terminology of the International League Against Epilepsy 1989).


CLINICAL MANIFESTATIONS

The average age of onset of epilepsy with myoclonic absences is 7 years (range: 2 to 12.5 years). Male preponderance has been described, but Manonmani and Wallace reported a female preponderance in a small series (Manonmani and Wallace 1994). About half of affected children are normal and half are mentally retarded prior to the onset of seizures (Tassinari and Bureau 1985; Tassinari et al 1992).

The manifestations are abrupt onset of absences accompanied by bilateral rhythmic myoclonic jerks of severe intensity.|{video:emat2a.avi}{caption:Myoclonic absence}{label:During hyperventilation, this male adult subject shows sudden jerking of both arms with associated partial loss of contact.}| The loss of consciousness during the absence may be complete or partial. The seizure mainly involves muscles of the shoulders, arms, and legs; facial muscles are less involved. When facial myoclonias occur, they are more evident around the chin and mouth, whereas eyelid twitching is typically absent or rare. The movements may be sustained and progressive, being associated with tonic contraction, which is maximal in shoulder and deltoid muscles. The jerks and tonic contractions may be symmetrical or predominant on one side, causing turning of the head and body. Autonomic manifestations such as arrest of respiratory movement and urinary incontinence may also be present (Tassinari and Bureau 1985; Tassinari et al 1992).

Each episode of myoclonic absences may last from 10 to 60 seconds. The seizures may occur many times a day. Hyperventilation, awakening, and stimulation by intermittent light can precipitate the attack. During sleep, however, the myoclonic seizures decrease in frequency with the progression of sleep stages (Tassinari and Bureau 1985; Tassinari et al 1992). Episodes of absence myoclonic status, though rare, have been described (Manonmani and Wallace 1994; Tassinari et al 1995).

Association with other types of seizures, such as generalized tonic-clonic, pure absence, and falling seizures, occurs in about two thirds of cases reported (Tassinari and Bureau 1985; Tassinari et al 1992).


ETIOLOGY

The etiology of epilepsy with myoclonic absences is unknown. Although a family history of seizure disorders can be found in about one fourth of cases reported, the genetic factors and hereditary mechanisms are not known. In a recent study, 7 out of 14 patients with myoclonic absence epilepsy showed evidence of a chromosome abnormality syndrome (trisomy 12 p and Angelman syndrome) (Elia et al 1998a; 1998b).


BIOLOGICAL BASIS

Both the pathogenesis and pathologic basis are unknown for epilepsy with myoclonic absences (Tassinari and Bureau 1985; Tassinari et al 1992). The recent evidence of associated chromosomal dysfunction in some cases suggests that abnormal expression of genes located in the affected chromosome segments may play a role in the pathogenesis of myoclonic absence epilepsy (Elia et al 1998a; 1998b).


EPIDEMIOLOGY

The syndrome is rare. Although figures of incidence or prevalence of epilepsy with myoclonic absences are unknown (Tassinari and Bureau 1985; Tassinari et al 1992), this syndrome was found in 0.5% to 1% of a selected population of epileptics in the Centre St. Paul of Marseille (Tassinari and Bureau 1985).


PREVENTION

No information is available.


DIFFERENTIAL DIAGNOSIS

The absences in epilepsy with myoclonic absences are similar to those in either childhood or juvenile absence epilepsies. Although those syndromes may also have associated myoclonic components, they are not generalized; they involve only eyelid or facial muscles and are much less intense than in epilepsy with myoclonic absences (Tassinari and Bureau 1985; Tassinari et al 1992). Moreover, mental impairment accompanies this syndrome much more frequently than in childhood juvenile absence syndromes.

Perioral myoclonus with absences, as described by Panayiotopoulos (Panayiotopoulos et al 1994), may share a similar evolution with myoclonic absences and may be considered a variant of this syndrome (Tassinari et al 1996). Differential diagnosis also includes generalized myoclonic jerks, which are not accompanied by loss of contact and are associated with distinctive polyspike and wave discharges, and partial motor seizures, which may be suspected because of the frequent asymmetrical motor manifestations in myoclonic absences. In these cases the EEG and polygraphic recording of the ictal events provides the clue to the correct diagnosis.


DIAGNOSTIC WORKUP

The ictal EEG in epilepsy with myoclonic absences shows a pattern of bilateral, synchronous, and symmetrical discharge of spike-waves at 3 Hz, similar to that of childhood absences (Tassinari and Bureau 1985; Tassinari et al 1992).|{diagram:emat1.bmp}{caption:Spontaneous myoclonic absence}{label:Rhythmic spike waves at 3-Hz. Rhythmic myoclonias begin 1 second after the onset of EEG paroxysmal discharges and are progressively associated with a tonic contraction. From Tassinari and Michelucci 1994, with permission)}|The discharges may end with delta waves in frontal areas, which may be asymmetrical. The spike-wave discharges may be interspersed with polyspike and wave activity (Tassinari et al 1995). Polygraphic recording of myoclonic absences discloses the appearance of bilateral myoclonias, at the same frequency as the spikes and waves, which begin 1 or 2 seconds after the onset of the EEG paroxysmal discharges and are followed by a tonic, sometimes asymmetrical, contraction, maximal in the deltoid and shoulder muscles (Tassinari and Bureau 1985; Tassinari et al 1992).|{diagram:emat1.bmp}{caption:Spontaneous myoclonic absence}{label:Rhythmic spike waves at 3-Hz. Rhythmic myoclonias begin 1 second after the onset of EEG paroxysmal discharges and are progressively associated with a tonic contraction. From Tassinari and Michelucci 1994, with permission)}|Oscilloscopic recordings demonstrate a strict and constant relationship between an initial positive transient of the spike and the myoclonia (Tassinari et al 1969). The interictal EEG findings include normal background activity in all cases with superimposed generalized spikes and waves or, more rarely, focal or multifocal spikes and waves. Photosensitivity is uncommon. The sleep EEG shows a normal organization and symmetrical physiological patterns. During sleep the evolution of the spikes and waves is similar, on the whole, to that observed in childhood absence epilepsy (Tassinari and Bureau 1985; Tassinari et al 1992;1996).


PROGNOSIS AND COMPLICATIONS

Epilepsy with myoclonic absences has a variable but often poor prognosis. The myoclonic absence seizures may persist into adulthood in about one half of the cases, whereas they disappear in the remaining patients after a mean period of 5.5 years from onset (Tassinari et al 1992). Patients with "refractory" myoclonic absence seizures have a high incidence (85%) of associated seizures, mostly tonic-clonic and falling seizures. In contrast, patients with "remitting" myoclonic absence seizures have a lower incidence of associated seizures, usually typical absences (Tassinari et al 1992). Medical therapy seems to influence the evolution of this syndrome. Recent observations indicate that a combination of valproate and ethosuximide at high doses with appropriate control of plasma levels leads to a rapid remission of myoclonic absences in most cases (Tassinari and Michelucci 1994). The therapeutic history of "refractory" cases often discloses that the above drugs were given at inadequate doses or that different drugs were used.

The long duration of myoclonic absences is likely to play a significant role for the appearance of mental deterioration, since mental functions do not worsen in children with rapid remission of myoclonic absences. Manonmani and Wallace postulated that mental deterioration may be the result of ongoing seizure activity (Manonmani and Wallace 1994).

In rare cases the disappearance of myoclonic absences has been followed by the onset of other seizure types, such as atypical absences and subclinical tonic seizures, giving rise to a clinical picture resembling the Lennox-Gastaut syndrome (Tassinari and Bureau 1985; Tassinari et al 1992).


MANAGEMENT

The combined use of valproate and ethosuximide at high doses—with corresponding plasma levels of 80 to 130 µg/mL and 70 to 110 µg/mL, respectively—is the therapy of choice for epilepsy with myoclonic absences. In individual cases, good seizure control may be achieved by a polytherapy with phenobarbital, valproate, and benzodiazepines (Tassinari et al 1992). Manonmani and Wallace as well as Appleton stress the usefulness of lamotrigine in management and, when this is not successful, it may be helped by the addition of valproate as a second drug (Appleton 1994; Manonmani and Wallace 1994).


PREGNANCY

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


ANESTHESIA

No information is available.


REFERENCES CITED

Appleton RE. Epilepsy with myoclonic absence. Arch Dis Child 1994;71:180.

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.

Elia M, Guerrini R, Musumeci SA, Bonanni P, Gambardella A, Aguglia U. Myoclonic absence-like seizures and chromosome abnormality syndromes. Epilepsia 1998a;39:660-3.

Elia M, Musumeci SA, Ferri R, Cammarata M. Trisomy 12p and epilepsy with myoclonic absences. Brain Dev 1998b;20:127-30.

Gibberd FB. The clinical features of petit mal. Acta Neurol Scand 1966;42:176-90.

Manonmani V, Wallace SJ. Epilepsy with myoclonic absences. Arch Dis Child 1994;70:288-90.

Panayiotopoulos CP, Ferrie CD, Giannakodimos S, Robinson RO. Perioral myoclonia with absences: a new syndrome? In: Wolf P, editor. Epileptic seizures and syndromes. London: John Libbey, 1994:143-53.

Tassinari CA, Bureau M. Epilepsy with myoclonic absences. In: Roger J, Dravet C, Bureau M, Dreifuss FE, Wolf P, editors. Epileptic syndromes in infancy, childhood and adolescence. London: John Libbey, 1985:121-9.

Tassinari CA, Bureau M, Thomas P. Epilepsy with myoclonic absences. In: Roger J, Bureau M, Dravet C, Dreifuss FE, Perret A, Wolf P, editors. Epileptic syndromes in infancy, childhood and adolescence. London: John Libbey, 1992:151-60.

Tassinari CA, Lyagoubi S, Santos V, et al. Etude des décharges de pointes ondes chez l'homme. II. Les aspects cliniques et electroencephalographiques des absences myocloniques. Rev Neurol 1969;121:379-83.

Tassinari CA, Michelucci R. Epilepsy with myoclonic absences: a reappraisal. In: Wolf P, editor. Epilepsic seizures and syndromes. London: John Libbey, 1994:137-41.

Tassinari CA, Michelucci R, Rubboli G, et al. Myoclonic absence epilepsy. In: Duncan JS, Panayiotopoulos CP, editors. Typical absences and related epileptic syndromes. Guildford: Churchill Communications Europe, 1995:187-95.

Tassinari CA, Rubboli G, Michelucci R. Epilepsy with myoclonic absences. In: Wallace J, editor. Epilepsy in children. London: Chapman & Hall, 1996:287-91.

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