What are the different types of seizures?

Types of Seizures

Seizures are classified into two main categories: focal seizures and generalized seizures, with additional classifications for seizures of unknown onset, based on the International League Against Epilepsy (ILAE) classification system. 1

Focal Seizures

Focal seizures originate within networks limited to one hemisphere of the brain and may be discretely localized or more widely distributed 2. They are further categorized by awareness level and motor/non-motor symptoms:

• Focal Aware Seizures (formerly simple partial seizures)

  • Patient remains conscious during the seizure
  • May include motor symptoms, sensory phenomena, autonomic features, or emotional/cognitive changes

• Focal Impaired Awareness Seizures (formerly complex partial seizures)

  • Consciousness is affected
  • Often include automatisms (repetitive, purposeless movements)
  • May include behavior arrest, hyperkinetic movements, autonomic symptoms, cognitive changes, or emotional manifestations 3

• Focal to Bilateral Tonic-Clonic Seizures (formerly secondarily generalized seizures)

  • Begin in one part of the brain but spread to involve both hemispheres 1, 3

Carbamazepine is indicated for partial seizures with complex symptomatology (psychomotor, temporal lobe) 4, while levetiracetam is considered first-line treatment for focal seizures due to its favorable side effect profile and minimal drug interactions 1.

Generalized Seizures

Generalized seizures originate at a point within the brain and rapidly engage bilaterally distributed networks, involving the thalamus and upper brainstem 1, 2. Types include:

1. Tonic-Clonic Seizures (formerly grand mal)

   • Characterized by rigid muscle contraction (tonic phase) followed by rhythmic muscle contractions (clonic phase)
   • Usually involve loss of consciousness

2. Absence Seizures (formerly petit mal)

   • Brief episodes of staring with impaired awareness
   • May include mild clonic, tonic, or atonic components
   • Note: Carbamazepine is not effective for absence seizures 4

3. Myoclonic Seizures

   • Brief, shock-like jerks of muscles
   • May occur in isolation or as part of syndromes

4. Tonic Seizures

   • Sustained muscle contraction without clonic phase

5. Clonic Seizures

   • Rhythmic jerking movements without tonic phase

6. Atonic Seizures

   • Sudden loss of muscle tone leading to falls (drop attacks)
   • Recent evidence shows many "drop attacks" are actually epileptic spasms rather than pure atonic seizures 5

7. Myoclonic-Atonic Seizures

   • Myoclonic jerk followed by atonic component 1, 3

8. Myoclonic-Tonic-Clonic Seizures

   • Myoclonic jerks preceding a tonic-clonic seizure 3

9. Epileptic Spasms

   • Brief contractions of muscles of the neck, trunk, and extremities 1

Valproate, lamotrigine, and topiramate are particularly effective for generalized seizures 1, 6.

Seizures of Unknown Onset

When the beginning of a seizure is not observed or unclear, it may be classified as:

• Unknown onset motor seizures
• Unknown onset non-motor seizures
• Unclassified seizures 3

Epilepsy Syndromes

Seizures often occur as part of specific epilepsy syndromes, including:

• Juvenile myoclonic epilepsy
• Juvenile absence epilepsy
• Infantile absence epilepsy
• Epilepsy with generalized tonic-clonic seizures only 1

Diagnostic Considerations

• MRI is superior to CT for identifying epileptogenic lesions, especially for focal seizures 1
• EEG monitoring is essential for detecting epileptic activity and classifying seizure types 1
• Distinguishing between epileptic and non-epileptic events is crucial to avoid inappropriate treatment 1

Common Pitfalls in Seizure Classification

• Mistaking syncope for seizures
• Failing to recognize that seizure types may change with age or treatment
• Not considering that some seizure types (atonic, clonic, epileptic spasms, myoclonic, and tonic) can have either focal or generalized onset 3
• Overlooking non-convulsive status epilepticus in patients with altered mental status 1
• Not recognizing that new-onset or poorly controlled seizures may indicate underlying pathology requiring neuroimaging 1

Understanding the correct classification of seizures is essential for appropriate treatment selection, as different antiepileptic medications have varying efficacy for different seizure types.