Early myoclonic encephalopathy

Early myoclonic encephalopathy (EME), also known as neonatal myoclonic encephalopathy or Aicardi syndrome (not to be confused with Aicardi-Goutières syndrome), is a severe epileptic syndrome that presents in the neonatal period, typically within the first three months of life. It is characterized by fragmentary or erratic myoclonus (irregular, jerky muscle movements), massive myoclonia, focal seizures, and tonic spasms. The electroencephalogram (EEG) characteristically shows a suppression-burst pattern, which may later evolve into hypsarrhythmia or other severely abnormal patterns. The condition primarily affects the central nervous system, leading to profound neurological impairment, severe intellectual disability, and marked developmental delay or regression. EME has multiple potential underlying etiologies, including inborn errors of metabolism such as nonketotic hyperglycinemia, organic acidurias (e.g., propionic acidemia, methylmalonic acidemia, D-glyceric acidemia), pyridoxine dependency, Menkes disease, and Zellweger syndrome. In some cases, structural brain malformations or genetic mutations may be identified, while in others the cause remains unknown (cryptogenic). The metabolic causes are frequently inherited in an autosomal recessive pattern, though the inheritance depends on the specific underlying etiology. The prognosis of early myoclonic encephalopathy is generally very poor. Most affected infants experience persistent, drug-resistant seizures that do not respond well to conventional antiepileptic medications. Treatment is largely supportive and symptomatic, focusing on seizure management and nutritional support. In cases where a treatable metabolic disorder is identified (such as pyridoxine-dependent epilepsy), specific metabolic therapy may provide some benefit. However, the majority of children with EME have severe neurodevelopmental impairment, and mortality in infancy or early childhood is high.

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