Epilepsy with Myoclonic Absences

Carlo Alberto Tassinari

Roberto Michelucci

Elena Gardella

Guido Rubboli

Introduction

Epilepsy with myoclonic absences (MAs) is an epileptic syndrome characterized clinically by absence seizures associated with rhythmic, bilateral myoclonic jerks of severe intensity. The diagnosis is based on clinical observation and ictal video-polygraphic recordings. Indeed, in video-polygraphic investigations (recording an electroencephalogram [EEG] and electromyogram [EMG] from upper limb muscles, such as deltoids), MAs are characterized by rhythmic, bilateral, synchronous, symmetric 3-Hz spike-wave (SW) discharge, as in typical absences, associated with EMG myoclonic bursts at 3 Hz, superimposed to a progressively increasing tonic contraction.

Demonstration of MA seizures is essential for the diagnosis; thus, epilepsy with MAs belongs to the group of epilepsy syndromes that is defined by a specific seizure type (as, for example, juvenile myoclonic epilepsy or myoclonic astatic epilepsy [Doose syndrome]). Indeed, since the early description of MAs,¹³^,¹⁵^,¹⁶ it has been believed that this seizure type could characterize a distinct epileptic condition that could be identified and separated from other forms of generalized epilepsy, such as childhood absence epilepsy. The Commission on Classification and Terminology of the International League Against Epilepsy (ILAE) accepted this view, recognizing epilepsy with MAs as an autonomous syndromic entity that was included, in the 1989 ILAE Proposal for Revised Classification of Epilepsies and Epileptic Syndromes,⁶ in the group of cryptogenic or symptomatic generalized epilepsies, due to an overall dismal and heterogeneous prognosis. On the other hand, in the more recent Proposed Diagnostic Scheme for People with Epileptic Seizures and with Epilepsy produced by the ILAE Task Force on Classification and Terminology,⁹ it has been tentatively placed among idiopathic generalized epilepsies. Recent reviews on this epileptic condition by Bureau and Tassinari²^,³ and Tassinari et al.²¹ acknowledged the existence of at least two forms of epilepsy with MAs: one with a more benign course, and eventually disappearance of seizures, in which MAs are the sole, or predominant, seizure type; and the other with MAs associated with other seizure types (particularly, frequent generalized tonic–clonic seizures) that bears a more severe prognosis, as compared to other idiopathic generalized epilepsies. Furthermore, cases with “atypical” features in which MAs were part of a clinical picture characterized by some degree of mental retardation, neurologic deficits (e.g., congenital hemiparesis), and chromosomopathy⁷^,⁸^,¹¹ have been reported.

Clinical Data

General Remarks

Epilepsy with MAs is a rare condition; in a selected population of epileptic patients attending the Centre St. Paul in Marseilles, it accounts for 0.5% to 1% of all epilepsies. There is a male preponderance (69%), at variance with childhood absence epilepsy in which females are more frequently affected. Etiologic factors reported in about 35% of cases are prematurity, perinatal damage, consanguinity, congenital hemiparesis, and chromosomopathy.²^,³ The evidence in some cases of associated chromosomal dysfunction has led to the hypothesis that abnormal expression of genes located in the affected chromosome segments may play a role in the pathogenesis of myoclonic absence epilepsy.⁷^,⁸ A genetic susceptibility, as demonstrated by a positive family history of epilepsies, has been observed in about 20% of cases.

The mean age of onset of MAs is 7 years, with a range between 11 months and 12.2 years. Reports describing cases with onset of MAs in the first year of life have been published in the last years.¹^,¹⁴^,¹⁹^,²²

Myoclonic Absences

MAs are characterized by the following:

Impairment of consciousness, which can vary in intensity, ranging from a mild disruption of contact to a complete loss of consciousness. Sometimes the patients are aware of the jerks and may recall the words pronounced by the examiner during the seizures.
Motor manifestations, which consist of bilateral myoclonic jerks, often associated with a discrete tonic contraction that has been clearly documented in proximal upper limb muscles. The myoclonias mainly involve the muscles of the shoulders, arms, and legs; facial myoclonias, when present, are more evident around the chin and the mouth, whereas eyelid twitching is typically absent or rare. Due to concomitant tonic contraction, the jerking of the arms is accompanied by a progressive elevation of the upper extremities, giving rise to a quite constant and recognizable pattern. When the patient is standing, falling is uncommon. In some patients, asymmetric features, such as head and trunk deviation, may occur.
Autonomic manifestations, which consist of an arrest of respiration and inconstant loss of urine.

MAs last for 10 to 60 seconds, and recur at a high frequency (many seizures per day), being often precipitated by hyperventilation or awakening. MAs may also be observed during the early stages of sleep. Episodes of MA status are distinctly rare.

Seizures Other Than Myoclonic Absences

MAs represent the only seizure type in about one third of patients. The remaining cases can suffer from other seizure types, which can appear before the onset of MAs or occur in association with MAs. They consist of generalized tonic–clonic seizures, absences, or epileptic falls.

Neurologic and Neuropsychologic Examination

Neurologic examination is normal, except in those cases with congenital hemiparesis. Mental retardation is present in about 45% of cases before the onset of MAs. During the course of MAs, mental retardation may worsen, or even appear, in patients previously normal, particularly in those patients with frequent tonic–clonic seizures associated with MAs. These data constitute a very significant difference for this subgroup of patients when compared with the cognitive status observed in childhood absence epilepsy.

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