Early myoclonic encephalopathy

Jules C Beal MD (Dr. Beal of Albert Einstein College of Medicine has no relevant financial relationships to disclose.)
Solomon L Moshé MD (Dr. Moshe of Albert Einstein College of Medicine received honorariums from UCB as a member of a data and safety monitoring board.)
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 October 18, 1993; last updated October 30, 2017; expires October 30, 2020

This article includes discussion of early myoclonic encephalopathy, neonatal myoclonic encephalopathy, myoclonic encephalopathy with neonatal onset, neonatal epileptic encephalopathy with periodic EEG bursts, and early myoclonic epileptic encephalopathy. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.

Overview

Early myoclonic encephalopathy is an epileptic encephalopathy syndrome with onset either in the neonatal period or within the first 3 months of life, characterized by erratic, fragmentary, or massive myoclonus, focal seizures, and late tonic spasms. The prognosis is severe. Early myoclonic encephalopathy and Ohtahara syndrome together are recognized as 2 of the epileptic encephalopathies seen in early infancy and characterized by suppression burst on electroencephalogram. In this updated article, the authors review the clinical and neurophysiological data, management, and etiologic factors. Early myoclonic encephalopathy is believed to have various prenatal etiologies that often remain unknown; inborn errors of metabolism and genetic disorders are sometimes found.

Key points

 

• Early myoclonic encephalopathy is an epileptic syndrome with onset either in the neonatal period or within the first 3 months of life.

 

• The syndrome is characterized clinically by erratic, fragmentary, or massive myoclonus, focal seizures, and tonic spasms and a suppression-burst pattern on EEG.

 

• Early myoclonic encephalopathy is believed to have various prenatal etiologies that often remain unknown; inborn errors of metabolism and genetic disorders are sometimes found.

 

• Prognosis is poor.

Historical note and terminology

Since 1978, numerous papers have been published that describe an epileptic syndrome with onset either neonatally or in the first months of life and characterized by erratic, fragmentary myoclonus, massive myoclonus, focal seizures, late tonic spasms, and EEG signs such as suppression-burst pattern. Various terms have been used: neonatal myoclonic encephalopathy (Aicardi and Goutieres 1978; Vigevano et al 1981), myoclonic encephalopathy with neonatal onset (Cavazzuti et al 1978), neonatal epileptic encephalopathy (Martin et al 1981), and early myoclonic epileptic encephalopathy (Dalla Bernardina et al 1983). The 1989 revised classification by the International League Against Epilepsy recognized this syndrome with the term "early myoclonic encephalopathy" and classified it under "symptomatic generalized epilepsies and syndromes with non-specific etiology" (Commission of Classification and Terminology of the International League Against Epilepsy 1989). The same Commission distinguished this syndrome from similar clinical pictures, such as "early infantile epileptic encephalopathy with suppression-burst" or Ohtahara syndrome.

In 2001, the International League Against Epilepsy Task Force on Classification and Terminology proposed to include early myoclonic encephalopathy in the list of epileptic encephalopathies (Engel and International League Against Epilepsy 2001). These are conditions in which not only the epileptic activity but also the epileptiform EEG abnormalities themselves are believed to contribute to the progressive disturbance in cerebral function. In addition to early myoclonic encephalopathy, this group also includes Ohtahara syndrome, West syndrome, Dravet syndrome, Lennox-Gastaut syndrome, Landau Kleffner syndrome, and electrical status epilepticus during sleep.

In 2010, the proposed organization presented by the Classification Commission of the International League Against Epilepsy included early myoclonic encephalopathy as an electroclinical syndrome distinguished by its clinical and EEG characteristics (Berg et al 2010).

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