Myoclonus epilepsy with ragged-red fibers
Nov. 06, 2023
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Early infantile epileptic encephalopathy (EIEE) is an epileptic encephalopathy syndrome with onset either in the neonatal period or within the first 3 months of life. It is characterized by a variety of seizure semiologies and characteristic EEG findings. The prognosis is severe. Distinct syndromes have been described, including early myoclonic encephalopathy and Ohtahara syndrome. However, there is considerable clinical overlap between them, and they may be considered a continuum of disease rather than distinct entities. In this article, the clinical, genetic, neurophysiologic, and etiologic data related to early infantile epileptic encephalopathy are reviewed.
• Early infantile epileptic encephalopathy is an epileptic syndrome with onset either in the neonatal period or within the first 3 months of life.
• The syndrome is clinically characterized by tonic spasms, myoclonus, or focal seizures and a suppression-burst pattern on EEG.
• Early infantile epileptic encephalopathy is believed to have various etiologies; genetic abnormalities, structural lesions, and metabolic disorders have all been implicated, or the etiology may remain unknown.
• Prognosis is poor.
Ohtahara syndrome and neonatal myoclonic encephalopathy were initially described as separate clinical entities in the 1970s (46; 02), and they continued to be classified that way for many years.
In the 1989 revised classification by the International League Against Epilepsy, these conditions remained distinct, and both were classified under "symptomatic generalized epilepsies and syndromes with non-specific etiology" (11). In 2001, the International League Against Epilepsy proposed to include both syndromes under the category of epileptic encephalopathies, 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 (16). In 2010, the proposed organization presented by the Classification Commission of the International League Against Epilepsy included both Ohtahara syndrome and early myoclonic encephalopathy as “electroclinical syndromes” distinguished by clinical and EEG characteristics (08).
Throughout this time, the term “early infantile epileptic encephalopathy” was also used in clinical practice, referring to a spectrum of epileptic encephalopathy syndromes occurring during infancy. In 2022 the International League Against Epilepsy Task Force on Nosology and Definitions recommended that the term “early infantile developmental and epileptic encephalopathy” be used for all of these conditions (58), noting that distinguishing between Ohtahara syndrome and early myoclonic encephalopathy “no longer provides valuable information for clinical decision-making or determination of prognosis” (61).
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