Myoclonic absences

C P Panayiotopoulos MD PhD (Dr. Panayiotopoulos of St. Thomas' Hospital has no relevant financial relationships to disclose.)
Jerome Engel Jr MD PhD, editor. (Dr. Engel of the David Geffen School of Medicine at the University of California, Los Angeles, has no relevant financial relationships to disclose.)
Originally released July 23, 1999; last updated April 18, 2017; expires April 18, 2020

Overview

Myoclonic absences are typical absence seizures with consistent, repetitive, and rhythmic myoclonic jerks during the ictus. The defining manifestations of typical absence seizures are impairment of consciousness and generalized 3 to 4 Hz spike-wave discharges. Clonic (rhythmic) and myoclonic (arrhythmic, singular) motor symptoms often feature at some stage of the absence, but these are rarely consistent, marked, and continuous. Myoclonic absences are mainly associated with the syndrome of “epilepsy with myoclonic absences” and “perioral myoclonia with absences.” Myoclonic absences are often misdiagnosed as focal motor seizures with adverse consequences on management. Effective antiepileptic medications are valproate, ethosuximide, lamotrigine, and clonazepam, usually in combination. In this updated article, the author details developments in the clinical and EEG manifestations, etiology, prognosis, differential diagnosis, and pharmacological treatment of myoclonic absences and related epileptic syndromes.

Key points

 

• Myoclonic absences are typical absence seizures with repetitive myoclonic jerks during the ictus.

 

• The classical type of myoclonic absences manifests with rhythmic jerks of shoulders, arms, and legs with a concomitant tonic contraction during 3 to 4 Hz generalized spike-wave discharges; this is the defining symptom of epilepsy with myoclonic absences.

 

• Another type of myoclonic absence seizures manifests with rhythmic jerks of perioral muscles during 3 to 4 Hz generalized spike-wave discharges; this is the defining symptom of perioral myoclonia with absences.

 

• Myoclonic absences start in childhood and usually continue into adult life, often combined with generalized tonic-clonic and other types of seizure.

 

• Etiology of epilepsy with myoclonic absences is varied whereas perioral myoclonia with absences is probably a genetically determined idiopathic generalized epilepsy.

 

• Myoclonic absences are often misdiagnosed as focal motor seizures though video-EEG recordings offer an unequivocal documentation of the correct diagnosis.

 

• Myoclonic absences are usually resistant to monotherapy with an appropriate anti-absence drug.

Historical note and terminology

The first report of absence seizures with severe clonic or myoclonic jerks appeared in 1966 (Gibberd 1966), but it was Tassinari and his associates who described and documented myoclonic absences and the syndrome of epilepsy with myoclonic absences (Tassinari et al 1969; Tassinari et al 1992; Tassinari et al 1995; Bureau and Tassinari 2005b; Bureau and Tassinari 2012).

Panayiotopoulos and associates described and documented perioral myoclonia with absences as a seizure type that may also constitute an epileptic syndrome (Panayiotopoulos et al 1994; Panayiotopoulos 2010).

ILAE Classification and nomenclature. Myoclonic absences are a type of typical absence seizures with significant and continuous rhythmic (2.5 to 4.5 Hz) clonic rather than myoclonic symptoms and have a tonic component.

Typical absence seizures are brief, generalized epileptic seizures of sudden onset and termination. They have 2 essential components: (1) clinically, the impairment of consciousness (absence) and (2) EEG generalized 3 to 4 Hz (more than 2.5 Hz) spike-and-slow wave discharges (Commission of Classification and Terminology of the International League Against Epilepsy 1981; Panayiotopoulos 2008). Impairment of consciousness may be the only clinical symptom (simple typical absence seizures), but this is often combined with other manifestations (complex typical absence seizures).

In appreciation of this diversity, the ILAE Task Force on classification recognized 4 types of typical absence seizures, probably of different pathophysiology and syndromic significance: (1) the classical absence seizures of childhood and juvenile absence epilepsy, (2) myoclonic absences, (3) phantom absences, and (4) eyelid myoclonia with absence (Engel 2006).

The ILAE proposals classify absence seizures as (1) typical, (2) atypical, (3) absence with special features (myoclonic absence and eyelid myoclonia) (Berg et al 2010; Commission on Classification and Terminology of the International League Against Epilepsy 2014; Fisher et al 2017a; Fisher et al 2017b).

Myoclonic absences (the seizures) may feature either in normal or neurologically and mentally abnormal children. Epilepsy with myoclonic absences (the syndrome) was previously categorized among the “cryptogenic or symptomatic generalized epilepsies and syndromes” (Commission on Classification and Terminology of the International League Against Epilepsy 1989). The ILAE diagnostic scheme considers only the idiopathic form, which probably represents less than a third of the whole spectrum of epileptic disorders manifesting with myoclonic absences (Engel 2001). The others are symptomatic or probably symptomatic cases. This syndrome is also recognized in the ILAE proposal and listed amongst the electroclinical syndromes with onset in childhood (Berg et al 2010).

Perioral myoclonia with absences has not been recognized either as a seizure type or as a syndrome by the ILAE. That absences with perioral myoclonia is a discrete seizure type has been unequivocally documented with video-EEG recordings (Panayiotopoulos et al 1994; Panayiotopoulos et al 1995; Hirsch 1995; Clemens 1997; Baykan and Noachtar 2005; d'Orsi et al 2011; Vrielynck et al 2011).

Image: Perioral myoclonia with absences (EEG)
Image: Perioral myoclonia with absences misdiagnosed as focal motor seizures (EEG)
Video: Perioral myoclonia with absences
Video: Perioral myoclonia with absences misdiagnosed as focal motor seizures
Video: Perioral myoclonia with absences manifesting with rhythmic twitching of the corners of the mouth and
Video: Typical absence seizures with continuous and repetitive myoclonic jerking of the eyebrows

The symptom of perioral myoclonia may also occur in absence seizures of idiopathic generalized epilepsy, and, as such, perioral myoclonia alone cannot be taken as sole evidence of the syndrome of perioral myoclonia with absences. However, there is often a non-fortuitous clustering of other symptoms indicating that these absences may often constitute the main symptom of a syndrome within the broad spectrum of idiopathic generalized epilepsy, which we proposed to call perioral myoclonia with absences (Panayiotopoulos et al 1994; Panayiotopoulos et al 1995; Panayiotopoulos 2005b). Other manifestations of this syndrome include: generalized tonic-clonic seizures (GTCS), which often start early prior to or together with the absences; frequent occurrence of absence status epilepticus; resistance to treatment; and persistence in adult life.

I also consider “eyelid myoclonia with or without absences” as mainly a myoclonic rather than absence epileptic seizure that is considered separately from the typical myoclonic absences (see Eyelid myoclonia).

In the ILAE “Epilepsy Diagnosis” manual, myoclonic absence seizures are considered as 1 of the 4 types of generalized absence seizures (typical, atypical, myoclonic, with eyelid myoclonia) and are described as follows (Commission on Classification and Terminology of the International League Against Epilepsy 2014):

Myoclonic absences. Myoclonic absences are rhythmic myoclonic jerks of the shoulders and arms with tonic abduction, which results in progressive lifting of the arms during the seizure. The myoclonic jerks are typically bilateral but may be unilateral or asymmetric. Perioral myoclonias and rhythmic jerks of the head and legs may occur. Seizures last 10 to 60 seconds and typically occur daily. Level of awareness varies from complete loss of awareness to retained awareness.

EEG Background. Please refer to specific syndrome in which this seizure type occurs.

Ictal EEG. Regular 3 Hz generalized spike-and-wave. EMG recordings from the upper arm show a constant relationship between the bilateral myoclonic jerks and spike-and-waves.

 

Caution. Slow spike-and-wave (<2.5 Hz), consider atypical absence seizures.

Differential diagnosis.

 

• Typical absence (with myoclonic components)
• Atypical absence

Related syndromes.

 

• Epilepsy with myoclonic absences

According to the newest position paper of the ILAE Commission for Classification and Terminology:

 

A myoclonic absence seizure refers to an absence seizure with rhythmic three-per-second myoclonic movements, causing ratcheting abduction of the upper limbs leading to progressive arm elevation, and associated with three-per-second generalized spike-wave discharges. Duration is typically 10 to 60 s. Impairment of consciousness may not be obvious. Myoclonic absence seizures occur in a variety of genetic conditions and also without known associations (Fisher et al 2017a; Fisher et al 2017b).

This latest ILAE classification proposes that:

 

Generalized seizures are divided into motor and nonmotor (absence) seizures. Nonmotor (absence) seizures are typical or atypical, or seizures that present prominent myoclonic activity or eyelid myoclonia. Further subdivisions are similar to those of the 1981 classification, with the addition of myoclonic-atonic seizures, common in epilepsy with myoclonic-atonic seizures (Doose syndrome), myoclonic-tonic-clonic seizures common in juvenile myoclonic epilepsy, myoclonic absence, and absence seizures with eyelid myoclonia seen in the syndrome described by Jeavons and elsewhere. Generalized manifestations of seizures can be asymmetrical, rendering difficult the distinction from focal-onset seizures. The word “absence” has a common meaning, but an “absent stare” is not synonymous with an absence seizure, since arrest of activity also occurs in other seizure types (Fisher et al 2017a; Fisher et al 2017b).

Further, this report clarifies that:

 

Seizures with eyelid myoclonia could logically have been placed under the motor category, but since eyelid myoclonia are most significant as features of absence seizures, seizures with eyelid myoclonia were placed in the nonmotor/absence category. Seizures with eyelid myoclonia may even rarely display focal features. Similarly, myoclonic absence seizures potentially have features of both absence and motor seizures, and could have been placed in either group (Fisher et al 2017a; Fisher et al 2017b).

Author's clarifications. According to the various ILAE classifications and definitions, generalized onset clonic seizures are mainly distinguished from generalized myoclonic seizures by their rhythmicity only and nothing else. This has created significant overlap in what to call clonic or myoclonic seizures, and often these terms are used interchangeably. An example of this is “myoclonic absence seizures” in which the motor component is clonic rhythmic at 2.5 to 4.5 Hz, rather than myoclonic arrhythmic.

Image: Myoclonic absence seizure of structural cause (EEG)
Image: Myoclonic absence seizure of unknown (idiopathic) cause (EEG)
Video: Myoclonic absence seizures of structural cause
Video: Myoclonic absence seizures of a boy with normal development (idiopathic)

Generalized clonic seizures, by definition, manifest with bilateral rhythmic clonic convulsions only. Their duration varies from minutes to hours, but each clonic event lasts less than 100 ms at a rate of 1 to 3 Hz . Conversely, myoclonic seizures are defined as singular or irregular recurrent events as opposed to the clonic seizures that are rhythmic at 1 to 5 Hz. Clonic seizures also differ from other types of seizure that manifest with tonic components mixed with myoclonus (eg, eyelid myoclonia) (Engel 2006).

The new ILAE position paper states that “clonic refers to sustained rhythmic jerking and myoclonic to regular unsustained jerking” and that “the distinction between clonic and myoclonic is somewhat arbitrary, but clonic implies sustained, regularly spaced stereotypical jerks, whereas, myoclonus is less regular and in briefer runs. Myoclonus differs from clonus by being briefer and not regularly repetitive. Myoclonus as a symptom has possible epileptic and nonepileptic etiologies” (Fisher et al 2017b). In the glossary of the same paper, myoclonic is defined as “sudden, brief (< 100 msec) involuntary single or multiple contraction(s) of muscles(s) or muscle groups of variable topography (axial, proximal limb, distal). Myoclonus is less regularly repetitive and less sustained than is clonus”, as opposed to clonic, which is “jerking, either symmetric or asymmetric, that is regularly repetitive and involves the same muscle groups” (Fisher et al 2017b).

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