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  • Updated 09.17.2020
  • Released 10.18.1993
  • Expires For CME 09.17.2023

Early myoclonic encephalopathy

Introduction

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 identified.

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 in the neonatal period 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 (03), myoclonic encephalopathy with neonatal onset (11), neonatal epileptic encephalopathy (32), and early myoclonic epileptic encephalopathy (15). 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" (14). 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 (18). 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 (10).

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