This presentation discusses the etiological classification of seizures

1. The Etiologic Classification of Epilepsy
By Dr Saumya Mittal

2. • The diagnostic process in clinical practice
comprises two stages:
– 1) the classification of the seizure type/syndrome and
– (2) the assignment of cause.
• ILAE Commission for Classification of the
Epilepsies has addressed etiology and divided
epilepsies into three categories
– genetic
– structural/metabolic
– unknown cause

3. • The classification of etiologies of the epilepsies is divided in 4 main categories.
• Definitions
• 1. Idiopathic epilepsy— epilepsy of predominately genetic or presumed genetic
origin and in which there is no gross neuroanatomic or neuropathologic
abnormality. Included are epilepsies of presumed multigenic or complex
inheritance, but for which currently the genetic basis has not been elucidated.
• 2. Symptomatic epilepsy— epilepsy of an acquired or genetic cause, associated
with gross anatomic or pathologic abnormalities, and/or clinical features,
indicative of underlying disease or condition. We thus include in this category
developmental and congenital disorders where these are associated with cerebral
pathologic changes, whether genetic or acquired (or indeed cryptogenic) in origin.
Also included are single gene and other genetic disorders in which epilepsy is only
one feature of a broader phenotype with other cerebral or systemic effects.
• 3. Provoked epilepsy—epilepsy in which a specific systemic or environmental
factor is the predominant cause of the seizures and in which there are no gross
causative neuroanatomic or neuropathologic changes. Some ‘‘provoked
epilepsies’’ will have a genetic basis and some an acquired basis, but in many no
inherent cause can be identified. The reflex epilepsies are included in this category
(which are usually genetic) as well as the epilepsies with a marked seizure
precipitant.
• 4. Cryptogenic epilepsy —epilepsy of presumed symptomatic nature in which the
cause has not been identified. The number of such cases is diminishing, but
currently this is still an important category, accounting for at least 40% of adult-
onset cases of epilepsy.

4. SYMPTOMATIC AND IDIOPATHIC
EPILEPSY

5. • This term is used only for those epilepsies that are primarily
genetic in origin and in which there is no gross
neuroanatomic or neuropathologic abnormality.
• In the framework proposed in this article, genetic
conditions that result in either pathologic or anatomic
change (for instance, the epilepsy due to tuberous sclerosis
or neurofibromatosis), or more subtle changes at the
molecular pathologic level (for examples the epilepsies due
to Rett syndrome, CDKL5, Angelman syndrome) are
included in the symptomatic category.
• Also included are epilepsies due to developmental
abnormalities where there are neuropathologic changes,
despite the fact that these are due to aberrant
development (and are sometimes largely genetic) rather
than to an external acquired cause. These developmental/
congenital disorders are a gray area between core
‘‘idiopathic’’ and core ‘‘acquired’’ epilepsies.

6. • The idiopathic epilepsies may have subtle
anatomic abnormalities, or synaptic,
membrane, neurotransmitter, or network
changes. The distinction from symptomatic
epilepsy, based as it is on the absence of a
‘‘gross lesion’’ (defined above as any
identifiable pathologic or anatomic
abnormality that can be detected in normal
clinical investigation, including clinical
microscopy, histology, and neurochemistry) is
to an extent, therefore, arbitrary.

7. PROVOKED EPILEPSY

8. • In the 19th century, it was fully recognized that most cases
of epilepsy had ‘‘exciting’’- environmental or sytemic
causes- as well as ‘‘predisposing’’ causes- stress, lack of
sleep, and so on.
• It is clear that seizure provocation can influence genetic
and acquired epilepsies and focal or generalized epilepsies,
and does not map easily across conventional seizure-type
or syndromic classifications.
• How such precipitants produce seizures is largely obscure.
• It is for this reason that the category has been included.
• Includes reflex epilepsies- the predominant cause is a
highly specific provocation and also the more common
seizure precipitants (stress, lack of sleep, and so on).
• Both generalized and focal seizures may be ‘‘provoked,’’
and provoked seizures can be either genetic or acquired.

9. ACQUIRED EPILEPSY
The term ‘‘acquired’’ is used to refer to ‘‘symptomatic’’ epilepsies
excluding the predominately genetic or developmental causes.

10. • Acute symptomatic epilepsy- include:
– Causes included as ‘‘provoking factors’’ such as
fever, metabolic disturbance, alcohol, and
– acute brain injury.
• Should be restricted to the latter.

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