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Understanding the etiology of a patient’s
epilepsy may allow the physician to provide prognostic information
and, most appropriately, manage the seizures. The classification
system most widely used for the epilepsies is the International
Classification of Epilepsies and Epileptic Syndromes set forth by
the International League Against Epilepsy (ILAE) (see Chapter 557).
Reflecting the importance of the cause underlying the epilepsy, this
system delineates 3 primary categories of etiological classification:
symptomatic, cryptogenic, and idiopathic.1 Symptomatic
epilepsy refers to epilepsy that is a symptom of a known underlying
cause, such as a structural brain lesion. Cryptogenic epilepsy,
sometimes called “presumed symptomatic” epilepsy,
occurs in children with other neurological abnormalities, suggesting
that the symptoms are referable to an underlying etiology, albeit
occult. Idiopathic epilepsy traditionally referred to epilepsy without
discernable predisposing cause in otherwise normal children, but
it has been increasingly evident that this category encompasses
epilepsies with genetic underpinnings.
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It is estimated that 20% to 40% of children
presenting with epilepsy have an identifiable etiology that would
place them in the symptomatic category.2 Nonetheless, the
consideration of a possible underlying etiology dominates the initial
evaluation of a child presenting with epilepsy. Many of the causes
listed below are identifiable using magnetic resonance imaging (MRI).
When MRI does not reveal an etiology for the epilepsy, further evaluation
of potential genetic and metabolic causes should be undertaken. Table 558-1 lists some of the major diagnostic
considerations that will motivate a thorough evaluation.
Many of the individual conditions are discussed in other chapters.
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Symptomatic epilepsy should be suspected in a child with epilepsy
in the following conditions: (1) any child with new onset of localization-related
(focal) epilepsy; (2) any child presenting with epilepsy with other neurological
symptoms, such as developmental delay, or signs, such as hemiparesis;
and (3) any child with a history or examination that leads to the
suspicion of a specific etiology. Uncovering a specific etiology
does not necessarily lead to a specific treatment based ...