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Historical note and nomenclature

The seizure entity of myoclonic absences was first described by Tassinari and colleagues (Tassinari et al 1969). Over the years, this seizure type has been reported by the same group, who related it to an epileptic syndrome with a similar name, “Epilepsy with myoclonic absences” (Tassinari and Bureau 1985; Tassinari et al 1992; 1995; 1996; Tassinari and Michelucci 1994). The diagnosis of myoclonic absence seizures is based on direct clinical criteria and ictal polygraphic recording.

Clinical manifestations

Myoclonic absences is a rare seizure type with a male preponderance (male>female, 2:1). The mean age of onset is 7 years (range: 9 months to 12 years). Age at onset as early as 6 months has been described (Verrotti et al 1999). The seizures are of sudden onset and offset, occurring especially soon after awakening, and can be precipitated by hyperventilation. The seizure duration ranges from less than 10 seconds to more than 2 minutes, and the seizure frequency is usually high.

The characteristics of myoclonic absences are as follows:

(1) Impairment of consciousness varies from mild, in which the patient can continue with normal activities such as playing with toys, to severe.

(2) Motor manifestations consist of rhythmic myoclonic jerks, primarily of the shoulders and arms and occasionally of the legs. In connection with myoclonic jerks of the shoulders, simultaneous jerks of the head also can be seen. Eyelid twitching is absent or rare, whereas perioral myoclonias may be frequent. Due to coinciding tonic contractions, the arms can be slightly elevated. The jerks and tonic contractions are usually bilateral but may be unilateral or asymmetric.

(3) Autonomic manifestations may occur as arrest or as a change of respiration and urination.

(4) The seizures are usually resistant to therapy.

Localization

No information was provided by the author.

Pathophysiology

The causes of myoclonic absences are poorly explained by current knowledge of the fundamental mechanisms of the epilepsies. However, in relation to recent chromosomal studies in other, more severe types of myoclonic absence seizures, also an abnormal expression of genes codifying for the subfamily of K+ channels and for gamma-aminobutyric acid-3 subunit receptors have been suggested (Elia et al 1998).

Differential diagnosis

Myoclonic absences are usually typical, and the diagnosis is mainly based on careful clinical observations and video-EEG studies with polygraphic recording (EMG of various shoulder and arm muscles). Clinically, the rhythmic myoclonic movements can be overlooked due to tonic contraction of the arm, or the intensity of the myoclonias can be reduced due to treatment. In these cases, absence seizures may be suspected. When the motor manifestations are asymmetric, partial seizures may be considered. It has been proposed that resistance to conventional treatment for absences with 3-Hz spike-wave activity is an indication of myoclonic absences, and adequate investigation should be performed.

Seizures similar to myoclonic absences may be seen in a variety of epileptic encephalopathies, including chromosome abnormality syndromes (Elia et al 1998), but a correct investigation will reveal the diagnosis. It must be emphasized that video-EEG studies are of utmost importance for differentiation of typical absence seizures (Panayiotopoulos et al 1989; Capovilla et al 2001).

Diagnostic workup

EEG. The ictal EEG comprises rhythmic generalized and bilateral synchronous and symmetric 3-Hz spike-wave activity as can be seen in typical absences. Occasionally, these classic discharges may be intermingled with polyspikes.

The interictal EEG shows a normal background activity with generalized irregular spike-wave activity (in one-third of the cases) that is sometimes intermingled with polyspikes; rarely, focal or multifocal spike-waves or spikes occur. Photosensitivity has been described in about one-third of patients (Tassinari et al 1992; Verrotti et al 1999). Sleep-EEG is usually normal with age-dependent physiological, including paroxysmal, patterns. However, 3-Hz spike-wave discharges may be seen, as may polyspikes and waves.

EMG. EMG during polygraphic recording shows myoclonias of the same frequency as the 3-Hz spike-wave activity.

Video-EEG with polygraphic recording. This (ie, EMG of various shoulder and arm muscles) is the single most important diagnostic procedure in myoclonic absences.

PET. Neuroimaging is rarely performed because the examinations usually have normal results. PET in idiopathic generalized epilepsy, especially absence epilepsy, has demonstrated normal cerebral glucose metabolism and benzodiazepine receptor density (Ryvlin and Mauguiere 1998).

Syndromes and diseases in which the seizure type occurs

Myoclonic absences are seen in epilepsy with myoclonic absences (Tassinari and Bureau 1985; Anonymous 1989; Tassinari et al 1995). Myoclonic absences have also been described in connection with learning difficulties, severe ataxia, and dyspraxia (Manonmani and Wallace 1994).

Prognosis and complications

Therapy resistance is common in myoclonic absences, with approximately 50% of the patients still having seizures after a follow-up of 10 years (Tassinari et al 1992). These patients also have a high incidence of associated seizures, mainly of generalized tonic-clonic and atonic types. In rare cases, a disappearance of myoclonic absences may be followed by the appearance of other seizure types, giving rise to a clinical picture similar to the Lennox-Gastaut syndrome. Behavioral problems are frequent, but mental retardation is present only in patients with poor seizure control (Verrotti et al 1999).

Management

Because of the therapy resistance of myoclonic absences, a spectrum of antiepileptic drugs have been tried. Drugs of first choice are those used in generalized epilepsies with absences or myoclonias. These are valproate and ethosuximide, usually in combination. Benzodiazepines or lamotrigine, eventually in combination with the other mentioned drugs, are another choice. However, benzodiazepines may worsen seizure behavior. In some cases, different new drugs, eg, levetiracetam (Krauss et al 2003) and topiramate (Bourgeois 2003), may be tried, as well as steroids and ketogenic diet (Manonmani and Wallace 1994). Carbamazepine, phenytoin, and vigabatrin usually are contraindicated. A new approach in therapy resistant cases may be the use of vagal nerve stimulator.

References cited

Anonymous. Proposal for revised classification of epilepsies and epileptic syndromes. Commission on Classification and Terminology of the International League Against Epilepsy. Epilepsia 1989;30(4):389-99.

Bourgeois BF. Chronic management of seizures in the syndromes of idiopathic generalized epilepsy. Epilepsia 2003;44 Suppl 2:27-32.

Capovilla G, Rubboli G, Beccaria F, et al. A clinical spectrum of the myoclonic manifestations associated with typical absences in childhood absence epilepsy. A video-polygraphic study. Epileptic Disord 2001;3(2):57-62.

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

Krauss GL, Betts T, Abou-Khalil B, Gergey G, Yarrow H, Miller A. Levetiracetam treatment of idiopathic generalised epilepsy. Seizure 2003;12(8):617-20.

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

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

Ryvlin P, Mauguiere F. Functional imaging in idiopathic generalized epilepsy. Rev Neurol (Paris) 1998;154:691-3.

Tassinari CA, Bureau M. Epilepsy with myoclonic absences. In: Roger J, Dravet CH, Bureau M, Dreifuss FE, Wolf P, editors. Epileptic syndromes in infancy, childhood, and adolescence. London: John Libbey and Company Ltd, 1985:123-31.

Tassinari CA, Bureau M, Thomas P. Epilepsy with myoclonic absences. In: Roger J, Bureau M, Dravet CH, Dreifuss FE, Perret A, Wolf P, editors. Epileptic syndromes in infancy, childhood and adolescence. 2nd ed. London: John Libbey and Company Ltd, 1992:151-60.

Tassinari CA, Lyagoubi S, Santos V, et al. Etude dés décharges de pointe-ondes chez l'homme. II. Les aspects cliniques et électroencéphalographiques des absensces myocloniques. Rev Neurol (Paris) 1969;121:379-83.

Tassinari CA, Michelucci R. Epilepsy with myoclonic absences: a reappraisal. In: Wolf P, editor. Epileptic seizures and syndromes. London: John Libbey and Company Ltd, 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. London: Churchill Livingstone, 1995:187-95.

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

Verrotti A, Greco R, Chiarelli F. Epilepsy with myoclonic absences with early onset: A follow-up study. J Child Neurol 1999;14:746-9.

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Abbreviations

ADHD:attention deficit hyperactivity disorder

EEG:electroencephalography

EMG:electromyography

FDG-PET:18-flourodeoxyglucose positron emission tomography

Synonyms

Epilepsy with myoclonic absences

Major keyword descriptors

absences

atypical absence seizures

cryptogenic generalized epilepsy

myoclonias

myoclonic seizures

perioral myoclonias

rhythmic myoclonic jerks

symptomatic generalized epilepsy

therapy resistant seizures

Minor keyword descriptors

behavioral problems

dyspraxia

epilepsy

impairment of consciousness

learning difficulties

photosensitivity

seizures

severe ataxia

Age of presentation

01-23 months

02-05 years

06-12 years

Age of typical presentation

02-05 years

06-12 years

Illustration captions

***None of these video clips are used because this manuscript structure has no clinical vignette (original submission included a clinical vignette and these videos)—dlc

Video clip 1:

Myoclonic absence of 122 seconds duration. Myoclonic jerks are seen in the arms with left preponderance. The boy keeps a toy in his right hand. The head is slightly turned to the left. Chewing movements are seen briefly. During the electrographic seizure the myoclonias seem to stop and the boy changes position. Thereafter the myoclonias start again. Later , still during the electrographic seizure, he extends his right arm with the toy in the hand and with the eyes open. During the whole seizure he is silent.

Video clip 2:

Myoclonic absence of 8 seconds duration. Myoclonic jerks are seen in the arms with some right preponderance together with head nodding, and the head is slightly turned to the right.

Video clip 3:

Myoclonic absence of 11 seconds duration. Myoclonic jerks are seen in the arms and the head. A slight movement of the body to the left is noticed.

Permuted topic, synonyms, variants

Myoclonic absences

absences, myoclonic

myoclonic absences, Epilepsy with

absences, Epilepsy with myoclonic

Related topics

Absence status epilepticus

Childhood absence epilepsy

Myoclonic status in nonprogressive encephalopathies

Differential diagnosis

absence seizures

partial seizures

epileptic encephalopathies

chromosome abnormality syndromes

Lennox-Gastaut syndrome