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Abstract
Epileptic encephalopathies (EE) are defined as a group of conditions in which the epileptiform abnormalities themselves on the EEG (interictal discharges) are believed to contribute to the progressive disturbance in cerebral function (motor abilities, cognition, behavior, mood) above and beyond what might be expected from the underlying pathology (e.g. cortical malformation) alone. This might be a matter of quantitative aspects since in each type of epilepsy such disturbances can occur and have to be discriminated from direct effects of etiological factors, reactions to seizures, and effects of AEDs.
The most accepted EE can be listed according to their age dependant occurence: (1) Epileptic encephalopathies with suppression bursts, (2) Migrating partial seizures, (3) Infantile Spasms (4) Severe myoclonic epilepsy of infancy, (5) Myoclonic epilepsy in non progressive encephalopathy, (6) Lennox-Gastaut syndrome, (7) Epileptic encephalopathy with continous spike waves during sleep, (8) Landau Kleffner syndrome (9) Myoclonic astatic epilepsy and (10) Rasmussen syndrome.
The Neonate
Early infantile Epileptic encephalopathy with suppression bursts (Ohtahara syndrome):
Epileptic encephalopathies with suppression bursts begin within the first 3 months of life, with various types of focal and generalized seizures, including spasms and myoclonus. The EEG demonstrates bursts, lasting several seconds, of polyspikes alternating with lack of electric activity, this combination being called “suppression bursts” This type of tracing may be recorded in both sleep and waking conditions, or mainly during sleep. In some cases, patients exhibit both tonic spasms and partial seizures. The suppression burst pattern may be asymmetric, affecting mainly the side of a cortical malformation, usually hemimegalencephaly or focal cortical dysplasia. Aicardi syndrome, olivary-dentate dysplasia, and schizencephaly are other conditions in which such tracings are encountered. However, in most cases, magnetic resonance imaging (MRI) does not disclose any brain lesion. In other cases, the patient’s exhibit erratic and massive myoclonus, MRI is normal, and there is familial recurrence. Non ketotic hyperglycinemia, methylmalonic or propionic acidemia, pyridoxine deficiency, and Menkes disease may cause such conditions, but in most cases, no inborn error of metabolism can be identified.
The distinction between these two conditions, respectively called early epileptic encephalopathy (EEE) and neonatal myoclonic encephalopathy (NME), may be difficult based on clinical and EEG features because brief spasms are difficult to distinguish from generalized myoclonus. from the therapeutic point of view, the distinction is, however, of great importance because vigabatrin (VGB) improves the first condition, but does not alter the downward stream of the second one. Conversely, the distinction between suppression bursts and hypsarrhythmia with extreme fragmentation in sleep also is difficult in many cases, because in EEE, the suppression burst tracing evolves into the more continuous asynchronous spike and slow-wave activity of hypsarrhythmia. In practice, it seems wise to initiate VGB treatment, unless there is a clearly established diagnosis of NME based on familial antecedents. In non responding cases, the administration of steroid treatment should be considered from the onset of the disorder. Although the cause of psychomotor deterioration remains unclear, high seizure frequency combined with nearly continuous so- called “interictal” paroxysmal activity both seem to contribute. It consists of hypertonia of posterior axial muscles with lack of any psychomotor acquisition.
Early Infancy
Migrating partial seizures:
Within the first 6 months of life, patients start with partial seizures, the frequency of which increases progressively to the point at which they become nearly continuous. The clinical expression of the seizures is often very mild, consisting of motor and/or autonomic features, but video/EEG recording shows consistent clinical expression according to the topography of the focal discharge that consists of rhythmic theta activity, affecting simultaneously different areas of the cortex; thus the eponym “migrating.” The psychomotor condition of the patient deteriorates with progressive hypotonia and loss of visual contact. Neuroradiologic and biochemical investigations are negative. There are no familial cases. Although at this late point, discharges randomly affect different parts of the brain often simultaneously, they may for several months remain restricted to one part of it, thus a challenge for surgical decisions in cryptogenic partial epilepsy during the first year of life. In the course of the disease, periods of high seizure frequency with worsening of psychomotor condition alternate with nearly seizure-free periods during which the condition improves. High seizure frequency is therefore likely to be the only cause of psychomotor deterioration, consisting of diffuse hypotonia with lack of any cognitive acquisition.