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INTRODUCTION

Epilepsy is not a single disease. Epilepsy may represent a primary disorder, often with an identified genetic cause, or it may be a symptom or result of another disease. Understanding the etiology of a patient’s epilepsy has important implications for management and prognosis. In 1989, the International League Against Epilepsy (ILAE) classified etiologies of epilepsy into 3 main categories: symptomatic, cryptogenic, and idiopathic. In 2010, the ILAE reorganized the epilepsies into having a structural/metabolic (previously “symptomatic”), unknown (previously “cryptogenic”), or genetic (previously “idiopathic”) cause. The ILAE classification systems of epilepsy are discussed in more detail in Chapter 549.

EPILEPSY WITH A STRUCTURAL/METABOLIC CAUSE

Sources have estimated that between 20% and 40% of children with epilepsy have a known cause for their seizures. Through a careful history, physical exam, and diagnostic testing including labs, electroencephalogram (EEG), and magnetic resonance imaging (MRI), a diagnosis may be reached. In some situations for which initial testing is unrevealing, enzymatic or genetic testing may be helpful to establish a diagnosis.

Structural/metabolic, or “symptomatic,” epilepsy is considered in a number of situations, specifically for any child with new-onset focal seizures, any child with concurrent developmental delay, or children with focal neurologic findings (such as weakness or a hemiparesis). The history and examination may also raise suspicion for a specific etiology for epilepsy. Depending on the condition, uncovering a specific etiology may help guide management and treatment.

There are more than 300 single-gene disorders associated with diseases that include epilepsy as a symptom (Table 550-1). Etiologies include malformations of cortical development, acquired structural abnormalities, inborn errors of metabolism, progressive myoclonic epilepsies, and other genetic syndromes with systemic manifestations. Many of these conditions are described further in other chapters.

TABLE 550-1STRUCTURAL/METABOLIC (“SYMPTOMATIC”) ETIOLOGIES FOR EPILEPSY

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