International Classification of Seizures

Seizures are divided first into two categories:

• Partial (focal)
  
  

  • simple partial seizures (with no alteration of consciousness or memory)
    
    
  • complex partial seizures (with alteration of consciousness or memory) 
    
    

• Generalized

Partial Seizures

Have onset in one particular part of the brain, resulting in focal symptoms such as twitching in an arm or face, a sensory change, or even the focal type of change in memory that occurs with temporal lobe seizures. 

• Simple Partial Seizures
  These can be motor seizures with twitching, abnormal sensations, abnormal visions, sounds or smells, and distortions of perception.  Seizure activity can spread to the autonomic nervous system, resulting in flushing, tingling, or nausea.  All such simple partial seizures will be in clear consciousness and with full recall on the part of the patient.  If the patient becomes confused or cannot remember what is happening during the seizure, then the seizure is classified as a complex partial seizure. 

• Complex Partial Seizures
  These previously were called "psychomotor seizures"�, "temporal lobe seizures"� or "limbic seizures"�.  These words are all synonyms.  Complex partial seizures may have an aura, which is a warning for the seizure, typically a familiar feeling (deja vu), nausea, heat or tingling, or distortion of sensory perceptions.  About half of the patients do not have any remembered aura.  During the complex partial seizure patients may fumble or perform automatic fragments of activity such as lip smacking, picking at their clothes, walking around aimlessly, or saying nonsense phrases over and over again.  These purposeless activities are called automatisms.  About 75 percent of people with complex partial seizures have automatisms.  Those who do not simply stop, stare and blank out for a few seconds to minutes.

Generalized Seizures

These apparently start all over the brain.  In fact, epilepsy specialists believe that generalized seizures originate in deep structures of the brain and simply project to the cortical surface where we can see the manifestations of the seizure emerge relatively simultaneously. 

Generalized seizures are divided into several categories as listed below.

• Absence Seizures
  Were previously called petit mal seizures.  Absence seizures usually have onset in childhood, but they can persist into adulthood. Absence seizures present with staring spells lasting several seconds, sometimes in conjunction with eyelid fluttering or head nodding.  These seizures can be difficult to distinguish from complex partial seizures that also may result in staring. Absence seizures usually are briefer and permit quicker recovery.  The EEG also helps to distinguish an absence from a complex partial seizure.

• Generalized Tonic-Clonic Seizures
  Were previously called grand mal seizures.  These seizures start with sudden loss of consciousness and tonic activity (stiffening) followed by clonic activity (rhythmic jerking) of the limbs.  The patient's eyes will roll up at the beginning of the seizure and the patient will typically emit a cry, not because of pain, but because of contraction of the respiratory muscles against a closed throat.  Generalized tonic-clonic seizures usually last one to three minutes.  The seizure itself is called an ictus.  After the seizure, the patient is "post-ictal"�: sluggish, sleepy and confused, variably for hours.  Any seizure can have a postictal period.
  
  Seizures that begin focally can spread to the entire brain, in which case a tonic-clonic seizure ensues.  It is important, however, to distinguish those that are true grand mal, generalized from the start, from those that start focally and secondarily generalize. Secondarily generalized seizures arise from a part of the brain that is focally abnormal.  Drugs used to treat primarily and secondarily generalized tonic-clonic seizures are different. Patients with secondarily generalized tonic-clonic seizures may be candidates for curative epilepsy surgery; (add link here) whereas, primarily generalized tonic-clonic seizures are not surgical candidates, because there is no seizure origin site (focus) to remove.

• Atonic Seizures
  These are epileptic drop attacks.  Atonic seizures typically occur in children or adults with widespread brain injuries.  People with atonic seizures suddenly become limp and may fall to the ground.  Football helmets are sometimes required to protect against serious injuries.

• Myoclonic Seizure
  This is a brief un-sustained jerk or series of jerks, less organized than the rhythmic jerks seen during a generalized tonic-clonic seizure.  Other specialized seizure types occasionally are encountered.

• Tonic Seizures
  These involve stiffening of muscles as the primary seizure manifestation.  Arms or legs may extend forward or up into the air.  Consciousness may or may not be lost.  By definition, the clonic (jerking) phase is absent. Classification can be difficult, because stiffening is a feature of many complex partial seizures.  Tonic seizures, however, are much less common than are complex partial or tonic-clonic seizures.

Patients can have more than one seizure type.  One seizure type may progress into another as the electrical activity spreads throughout the brain.  A typical progression is from a simple partial seizure, to a complex partial seizure (when the patient becomes confused), to a secondarily generalized tonic-clonic seizure (when the electrical activity has spread throughout the entire brain).  The brain has control mechanisms to keep seizures localized.  Antiepileptic medications enhance the ability of the brain to limit spread of a seizure.

Adult Seizure Types 

Complex partial seizures - 40% 

Simple partial seizures - 20%

Primary generalized tonic-clonic seizures - 20%

Absence seizures - 10%

Other seizure types - 10%

In a pediatric population, absence seizures occupy a greater proportion.