Myoclonus epilepsy with ragged-red fibers
Nov. 06, 2023
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Seizures are the most common neurologic emergency in the neonatal period. Depending on etiology and whether seizure burden is high, seizures are associated with increased mortality and neurodevelopmental sequelae. Although seizure duration is typically brief in neonates, seizure burden can be very high. If the summed seizure duration is more than 50% of a given time epoch, it is considered neonatal status epilepticus. However, no consensus on its definition exists. Status epilepticus has been redefined by the International League Against Epilepsy, but this definition does not take the specificities of neonatal status epilepticus into account. A new ILAE task force has been created to define this in neonates.
• Neonatal status epilepticus is poorly defined, but the most commonly used definition by the American Clinical Neurophysiology Society defines it as a condition in which the summed seizure duration is more than 50% of a given time epoch.
• The etiologies of neonatal status epilepticus are similar to those of neonatal seizures and are most often acute provoked rather than part of an existing epilepsy syndrome.
• Around 15% to 30% of neonates with seizures have a period or periods of status epilepticus, but overall, the incidence is higher in neonates with hypoxic-ischemic encephalopathy and inborn errors of metabolism.
• Status epilepticus is nearly always electrographic-only and, thus, requires diagnosis with EEG.
• There is no evidence base for the treatment of neonatal status epilepticus and, consequently, current recommendations are similar to those for neonatal seizures.
In contrast to older children and adults, the definition of status epilepticus in neonates is not well defined. The following three concepts are currently in use.
Scher proposed neonatal status epilepticus as continuous seizure activity for at least 30 minutes or recurrent seizures for 50% or more of the recording time (40). Based on the Scher definition, with some modifications of the time epoch, the American Clinical Neurophysiology Society (ACNS) defined neonatal status epilepticus as being present when the summed duration of electrographic seizures comprises more than 50% of an arbitrarily defined 1-hour epoch (47).
Pisani based his definition of neonatal status epilepticus on the definition used for older children: continuous seizure activity for at least 30 minutes or recurrent seizures lasting a total of 30 or more minutes without definite return to baseline mental or neurologic condition (32). However, the majority of neonates with seizures have some degree of encephalopathy and sedation, making a clear return to baseline difficult, or even impossible, to evaluate.
The International League Against Epilepsy (ILAE) published a new definition of status epilepticus independent of age: status epilepticus is a condition resulting from failure of mechanisms responsible for seizure termination or from initiation of mechanisms leading to abnormally prolonged seizures (time point T1), which can have long-term consequences (time point T2), including neuronal death, neuronal injury, and alteration of neuronal networks, depending on type and duration (46). The classification system consists of four axes, which provide a framework for diagnosis and treatment. The four axes are (1) semiology, (2) etiology, (3) electroencephalography, and (4) age. Although the fourth axis includes the neonatal period, there is little consensus concerning the definition points T1 and T2 for this age group, which makes this definition difficult to use.
There is animal evidence that the immature hippocampus is more resistant to status-induced injury than the mature hippocampus (23). At the same time, clinical data indicate that outcome after neonatal seizures is related to seizure burden; specifically, the risk of poor outcome increases above a seizure burden of more than 12 to 13 min/h, even after adjusting for other important contributors to outcome such as seizure cause and illness severity (29; 18; 31; 09; 05; 03). Furthermore, it has been suggested that there is a higher risk of status epilepticus if treatment is commenced more than 2 hours after seizure onset (25).
Most neonatal seizures have a duration of less than 5 minutes, although overall seizure burden may be high (44; 07). Abend and colleagues suggested that in the absence of more rigorously defined parameters, it is probably useful in clinical practice to regard seizures that last longer than 5 minutes as extended or prolonged and to define status epilepticus as seizures that last longer than 30 minutes when researching the effect of seizure burden on outcome (01).
In summary, in the absence of a generally adopted definition for neonatal status epilepticus, the ACNS definition is most applicable to clinical practice. Additionally, the ILAE neonatal taskforce is working on a new definition for neonatal status epilepticus.
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