Epileptic encephalopathy syndromes are disorders in which the epileptiform abnormalities are thought to contribute to a progressive cerebral dysfunction. Characteristic electroencephalogram findings have an important diagnostic value in classification of epileptic encephalopathy syndromes. In this paper, we focus on electroencephalogram findings of childhood epileptic encephalopathy syndromes and provide sample illustrations. 1. Introduction Epilepsy electroclinical syndromes have characteristic seizure semiology, frequency, duration, inciting factors, and age of seizure onset and are often associated with specific electroencephalogram (EEG) findings. Epileptic encephalopathies are syndromes in which the epileptiform abnormalities are thought to contribute to a progressive cerebral dysfunction. The ictal and interictal EEG patterns can help define the electroclinical syndromes, identify potential etiologies, and guide treatment. A detailed description of each genetic etiology is beyond the scope of this review. This review focuses on the neurophysiological features, including variant patterns relevant to selected etiologies (Table 1). Table 1: Summary of clinical characteristics and EEG features at presentation in early and childhood onset epileptic encephalopathy. 2. Neonatal/Infantile Onset Epilepsy Syndromes 2.1. Early Infantile Epileptic Encephalopathy 2.1.1. Clinical Presentation Ohtahara first recognized early infantile epileptic encephalopathy (EIEE) in neonates who suffered frequent tonic seizures and subsequently developed significant intellectual disability [1]. Later studies of infants with EIEE show average seizure onset within 2-3 months after birth. Brief tonic seizures occur hundreds of times per day, often in clusters of 10 to 40 seizures. Focal seizures present as tonic eye deviation or unilateral clonic contractions. Myoclonic seizures are not a prominent feature [2]. 2.1.2. Long-Term Prognosis Mortality in EIEE is high during childhood, with 50% dying during the first 2 years of life [2]. Survivors into childhood have pharmacoresistant epilepsy with severe intellectual disability. EIEE evolves to West syndrome during infancy in 75%, Lennox-Gastaut syndrome in older children, or focal epilepsy [3]. 2.1.3. Etiologies Cerebral structural abnormality is the most common etiology of EIEE. However, in 13–38% of patients, STXBP1 mutation results in synaptic vesicle protein with impaired neurotransmitter release [4–6]. Children with STXBP1 mutation develop a paroxysmal movement disorder during infancy, which persists beyond the intractable
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