Seizures are symptoms of a brain problem. They happen because of sudden, abnormal electrical activity in the brain.  Seizures fall into two main groups. Focal seizures, also called partial seizures, happen in just one part of the brain. Generalized seizures are a result of abnormal activity on both sides of the brain.
Generalized Onset: Generalized seizures affect both sides of the brain or large networks of cells on both sides from the beginning of the event. The networks can be on the surface of the brain or involve deeper areas. Generalized seizures don’t need to involve the entire brain, just part of both sides.
Focal Onset: The term focal seizure has been used for years, but the lay public and many professionals still use the term partial seizures. In this 2017 Classification, focal seizures will replace partial seizures and refer to those that start in an area or network on one side of the brain. They may start on the surface of the brain or in deeper areas, and can be very localized or spread to larger areas. Sometimes more than one network is involved.
Unknown Onset: Seizures may be of unknown onset if the beginning of the seizure is not clear. As more information becomes available over time or through testing, the type of seizure may be changed to a generalized or focal onset seizure.
Generalized Motor Seizures :

  • Tonic-clonic – No change (Years ago the term grand mal was used)
  • Clonic – No change
  • Tonic – No change
  • Myoclonic – No change
  • Myoclonic-tonic-clonc – New term
  • Myoclonic-atonic – New term
  • Atonic – No change
  • Epileptic spasms – New term

Generalized Non-Motor Seizures (Absence)

  • Typical Absence – No change (Years ago the term petit mal was used)
  • Atypical absence – No change
  • Myoclonic absence – New term
  • Eyelid myoclonia – New term

Partial (Focal) Seizures
Partial (focal) seizures refer to seizures beginning in one area of the brain. By observing which area of the body is affected by the seizure, physicians can identify where in the brain the seizure occurred. 
Partial seizures are further categorized as either:
Simple partial seizures – The seizure is localized to one area on one side of the brain, but may spread to other areas. Consciousness is not lost during a simple partial seizure.
Complex partial seizures – Seizures originating in one area of the brain that affect consciousness are labeled as complex partial seizures.
Partial seizures that secondarily generalize – Partial seizures may spread to other areas of the brain. 

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