Expanded Seizure Classifications
Order and simplification are the first steps toward the mastery of a subject. - Thomas Mann

Epilepsy is a complex network disease. With expanding knowledge and understanding of epilepsy based on improved neuroimaging, genetics, and neurophysiology techniques, there have been many revisions and updates to the classification of epilepsy.

Does seizure classification matter?

  • Classification is a dynamic process that helps us understand and allows us to group seizures by types as science evolves.
  • It gives us a communication framework to analyse patients.
  • It provides a universal, common language that is easily understood by diverse audiences, such as patients and their caregivers, clinicians, neurologists, epileptologists, pharmacists, researchers, and more - all of whom are interested in patient care, teaching, and clinical trials.
  • It allows us to establish a definitive diagnosis, select appropriate therapeutics, and offer long term prognosis.
  • It helps us define epilepsy syndromes, predict mixed seizure types that are likely to evolve, identify potential seizure triggers, predict niche drugs that are expected to be effective, and increase awareness of epilepsy comorbidities including cognitive and psychiatric issues.

Operational Classification of Seizure Types by the International League Against Epilepsy

Clinical and electroencephalographical classification of seizures was first presented by Gastaut in 1969.1 The International League against Epilepsy (ILAE) Classification of Seizures (1981) and the Classification of the Epilepsies (1989) is currently widely used. A revised classification was proposed in 2010.

A further revision in 2017 has provided us with a new operational or a practical classification of epilepsy. The 1981 epilepsy classification broadly divided seizure types into simple or complex partial and generalized. It had some limitations.

  • Some seizures within the generalized type can be focal onset, such as focal onset spasms or focal tonic seizures, and prior classifications did not allow us to classify them as such.
  • Some seizures are simply difficult to classify whether they are focal or generalized at the onset. These unclassifiable seizures had no placement in previous classifications.
  • Level of consciousness is hard to determine in some seizures.
  • Terms such as psychic and dyscognitive were not clearly understood in the community.
  • Epilepsies such as absence with eye lid myoclonia or myoclonic absences were not included.

The new operational classification of seizure types by the International League Against Epilepsy includes the following 8 changes.2

  1. “partial” becomes “focal”
  2. awareness is used as a classifier of focal seizures
  3. the terms dyscognitive, simple partial, complex partial, psychic, and secondarily generalized are eliminated
  4. new focal seizure types include automatisms, behavior arrest, hyperkinetic, autonomic, cognitive, and emotional
  5. atonic, clonic, epileptic spasms, myoclonic, and tonic seizures can be of either focal or generalized onset
  6. focal to bilateral tonic-clonic seizure replaces secondarily generalized seizure
  7. new generalized seizure types are absence with eyelid myoclonia, myoclonic absence, myoclonic-atonic, myoclonic-tonic-clonic
  8. seizures of unknown onset may have features that can still be classified

Framework: Is it a seizure? If so, is it epilepsy? What type and what syndrome? What is the cause?

The first and foremost challenge a clinician faces is to recognize if a clinical event in question is a seizure. If it is a seizure, is it an epileptic phenomenon with a higher tendency for recurrence. There are several potential mimickers of seizures that can present with loss of consciousness or abnormal movements, such as a fainting spell or a sleep arousal phenomenon. ILAE’s website, epilepsydiagnosis.org, is an excellent resource with insights into epilepsy differential diagnosis and epilepsy classification, including types, syndromes, and etiology.

Once a seizure diagnosis is identified, the next step is to classify the type of seizure as focal, generalized, or unknown based on clinical history and supplemented with other data that is available, including home videos, EEG, and imaging findings. Based on patient’s age, specific clinical presentation, EEG features, and potential triggers, one can further classify epilepsy into specific epilepsy syndrome that may provide useful insight in to pharmaco responsiveness, age at remission, and long term prognosis.

  • Severe epilepsies that start early in life are classified as early onset epileptic encephalopathies.4 These are due to varied etiologies and are often treatment resistant causing developmental delays along with cognitive and behavioural impairments.
  • Even though age-specific epilepsies such as childhood absence or Rolandic epilepsies are considered benign, they are now best classified as self-limited, pharmacoresponsive epilepsy.
  • Epilepsy comorbidities, such as inattention, cognitive and learning delays, and psychosocial issues, may persist well beyond seizure control.5

A tailored diagnostic work up is often initiated with a hope to understand a possible underlying cause for epilepsy, such as a structural, genetic, infectious, and metabolic or an immune etiology.

Epilepsy Syndromes
 

Such a framework as indicated above is essential to have a systematic and orderly approach in patients diagnosed with epilepsy. Accurate classification of epilepsy as outlined above not only improves communication with families when discussing treatment options and long term prognosis, but also is fundamental in promoting collaborative research among community physicians and larger epilepsy centers.

References

  1. Gastaut H. Clinical and electroencephalographical classification of epileptic seizures. Epilepsia. 1969; 10:S2-13.
  2. Fisher, R. S., Cross, J. H., French, J. A., Higurashi, N., Hirsch, E., Jansen, F. E., Lagae, L., Moshé, S. L., Peltola, J., Roulet Perez, E., Scheffer, I. E. and Zuberi, S. M. (2017), Operational classification of seizure types by the International League Against Epilepsy: Position Paper of the ILAE Commission for Classification and Terminology. Epilepsia, 58: 522-530.
  3. Scheffer, I. E., et al. “ILAE Classification of the Epilepsies: Position Paper of the ILAE Commission for Classification and Terminology.” Epilepsia 2017; 512-521,
  4. Berg, A. T., Berkovic, S. F., Brodie, M. J., Buchhalter, J., Cross, J. H., Van Emde Boas, W., Engel, J., French, J., Glauser, T. A., Mathern, G. W., Moshé, S. L., Nordli, D., Plouin, P. and Scheffer, I. E. (2010), Revised terminology and concepts for organization of seizures and epilepsies: Report of the ILAE Commission on Classification and Terminology, 2005–2009. Epilepsia, 51: 676–685.
  5. Wirrell EC, Camfield CS, Camfield PR, Dooley JM, Gordon KE, Smith B. Long-term Psychosocial Outcome in Typical Absence Epilepsy Sometimes a Wolf in Sheeps' Clothing. Arch Pediatr Adolesc Med. 1997; 151(2):152-158.

Learn More About Seizure Classifications

Authored By: 
Anu Venkat MD
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Authored Date: 
07/2017
Reviewed By: 
Joseph I. Sirven MD
on: 
Saturday, July 1, 2017