Symptomatic Generalized Epilepsy

Updated: Dec 30, 2015
  • Author: Emily Nakagawa, DO, MPH; Chief Editor: Selim R Benbadis, MD  more...
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Overview

Background

Symptomatic generalized epilepsy (SGE) encompasses a group of challenging epilepsy syndromes. As a group, SGE has 3 main features: (1) multiple seizure types, especially generalized tonic and atonic seizures; (2) brain dysfunction other than the seizures, in the intellectual domain (mental retardation or developmental delay) and in the motor domain (cerebral palsy); and (3) EEG evidence of diffuse brain abnormality.

The following are examples of epilepsy syndromes that are included in the category of SGE:

  • Early myoclonic encephalopathy
  • Early infantine epileptic encephalopathy with suppression bursts or Ohtahara syndrome
  • West syndrome
  • Epilepsy with myoclonic atonic seizures
  • Epilepsy with myoclonic absence
  • Lennox-Gastaut syndrome
  • Progressive myoclonic epilepsies

See the following Medscape Reference epilepsy topics for more information on these conditions:

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Pathophysiology

Overall, seizures are a paroxysm of high-frequency or synchronous low-frequency high-voltage electrical discharges that cause a sudden alteration in the CNS. Three conditions are involved: (1) population of pathologically excitable neurons, (2) an increase in excitatory glutaminergic activity, and (3) reduction of inhibitory GABAergic projections. [1] In symptomatic generalized epilepsy, an underlying structural or metabolic derangement is also present. EEG findings reflect age-related changes as the brain matures. [2]

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Epidemiology

Frequency

Assessing the frequency of symptomatic generalized epilepsy (SGE) is difficult because the definition varies and can be more or less inclusive.

In a study by Ohtahara and Yamatogi, 12 of 16 patients with Ohtahara syndrome developed into West syndrome or infantile spasms between ages 3 and 6 months as defined by EEG findings. [3] Infantile spasms affect 1 in 2000 infants. [4] Lennox-Gastaut syndrome has an incidence of 1.9-2.1 cases per 100,000 children and accounts for 6-7% of intractable pediatric epilepsy; however, this depends of the definition used for Lennox-Gastaut syndrome.

Mortality/Morbidity

A study of social outcomes in a Nova Scotia study found that 20 years after diagnosis of childhood-onset symptomatic generalized epilepsy (SGE), 25% die. All survivors have mental retardation and depend on parents and institutions in terms of living and finances. [5] Most patients with SGE grow up to have intractable epilepsy, with a small percentage who are seizure free with no antiepileptic drugs. [5] In a follow-up study of 14 patients with Ohtahara syndrome, 4 died early and the remaining 10 were severely handicapped. [6]

Age

These refer to age at onset. In adulthood, most patients with symptomatic generalized epilepsy (SGE) have a less well-defined syndrome that still has the characteristics of SGE and is closest to a Lennox-Gastaut syndrome (intractable multiple seizure types, mental retardation, and cerebral palsy). Note the following progression:

  • Neonates - Early myoclonic encephalopathy, early infantine epileptic encephalopathy with suppression bursts, or Ohtahara syndrome
  • Infancy - West syndrome
  • Childhood - Epilepsy with myoclonic atonic seizures, epilepsy with myoclonic absence, Lennox-Gastaut syndrome
  • Adolescence-adults - Progressive myoclonic epilepsies
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