Lennox-Gastaut syndrome (LGS) can be classified according to its suspected etiology as either idiopathic or symptomatic. Population-based studies have found that 22–30% of patients have idiopathic LGS and 70–78% have symptomatic LGS.21,22,27,28

Patients may be considered to have idiopathic LGS21 if:

• normal psychomotor development is noted before the onset of symptoms
• no underlying disorders or definite presumptive causes are known
• no neurologic or neuroradiologic abnormalities are seen

In contrast, patients are considered to have symptomatic LGS if an identifiable factor is responsible for the syndrome. Examples of underlying pathologic processes responsible for symptomatic LGS include:20,21, 25

• encephalitis or meningitis
• tuberous sclerosis
• brain malformations (e.g., cortical dysplasias)
• birth injury
• hypoxia-ischemia injury
• frontal lobe lesions
• trauma

Infantile spasms precede the development of LGS in 9–39% of cases.16,23,25

Some investigators consider cryptogenic LGS as a separate etiologic category, in which the epilepsy is presumed to be symptomatic but no cause is identified. In an epidemiologic study in Atlanta, 44% of all LGS patients were classified in the cryptogenic group.23

Adapted from: Glauser TA and Morita DA. Lennox-Gastaut syndrome. In: Devinsky O and Westbrook LE, eds. Epilepsy and Developmental Disabilities. Boston: Butterworth-Heinemann; 2001;65–78.
With permission from Elsevier (www.elsevier.com).
Reviewed and revised May 2004 by Steven C. Schachter, MD, epilepsy.com Editorial Board.