What are focal onset seizures?

Focal Onset Seizures: Definition, Classification, and Management

Focal seizures are defined as seizures that originate in a specific area of one hemisphere of the brain, which may remain localized or spread to become more widely distributed. 1, 2

Definition and Classification

• Focal seizures originate within networks limited to one hemisphere of the brain, as defined by the International League Against Epilepsy's (ILAE) operational classification system 2
• Focal seizures are categorized based on awareness level into two main types 1, 2:
  • Focal aware seizures (retained awareness)
  • Focal impaired awareness seizures (formerly known as complex partial seizures)
• Some focal seizures can progress to bilateral tonic-clonic seizures (formerly known as focal seizures with secondary generalization) 1, 3

Clinical Presentation

• Motor manifestations may include 1, 2:
  • Jerking of one extremity or one side of the body
  • Abnormal facial movements
  • Small repetitive movements
• Non-motor manifestations may include 1, 2:
  • Staring spells (focal impaired awareness)
  • Sensory symptoms (tingling, numbness)
  • Autonomic symptoms (flushing, sweating)
  • Cognitive or emotional changes
• Urinary incontinence may occur during a seizure 1
• Most seizures are followed by a postictal period where the person appears tired and confused for several minutes 1

Epidemiology and Significance

• Focal seizures have a high recurrence rate of up to 94%, which is considerably higher than generalized seizures (72%) 1
• Positive yields from neuroimaging of patients with focal seizures are considerably higher compared to patients with generalized seizures who have a normal neurologic examination 1
• The presence of any focal feature to a seizure is independently associated with clinically relevant abnormalities on neuroimaging 1

Diagnostic Approach

• MRI is the preferred neuroimaging modality for focal seizures as it is more sensitive than CT in detecting brain abnormalities 1, 2
  • MRI can detect developmental abnormalities, hemorrhage, neoplasm, and gliosis 1, 2
  • In children with seizures, MRI demonstrates focal brain abnormalities in 55% of cases, whereas CT is positive in only 18% 1
  • An optimized epilepsy protocol with adequate spatial resolution and multiplanar reformatting is essential for detecting epileptogenic lesions 1
• EEG, detailed history from the patient and eyewitnesses, and neuroimaging are essential components of the diagnostic workup 4
• Video EEG to record ictal events may be necessary to establish the correct diagnosis in complex cases 4

First Aid Management

• First aid providers should activate EMS for individuals with 1:
  • First-time seizure
  • Seizures lasting >5 minutes
  • Multiple seizures without return to baseline mental status between episodes
  • Seizures occurring in water
  • Seizures with traumatic injuries, difficulty breathing, or choking
  • Seizure in an infant <6 months of age
  • Seizure in pregnant individuals
  • If the individual does not return to baseline within 5-10 minutes after seizure activity stops
• First aid providers should minimize injury risk by 1:
  • Helping the person to the ground
  • Placing the person on their side in the recovery position
  • Clearing the area around them
• First aid providers should stay with the person having a seizure 1

Mechanisms and Patterns of Focal Seizure Onset

• Two main onset patterns have been identified in focal seizures 5:
  • Low amplitude fast oscillations (LAF)
  • High amplitude spikes (HAS)
• These patterns are associated with different mechanisms 5:
  • LAF onset involves independent patches of localized activity that slowly invade surrounding tissue and coalesce over time
  • HAS onset represents a global, systemic transition to a seizure state triggered by a local event
• The excitability of tissue surrounding the seizure focus may play a determining role in the seizure onset pattern and surgical outcomes 5

Management Considerations

• Patients with focal epilepsy who become drug-resistant should be promptly assessed in an epilepsy center 3
• Referral to a comprehensive epilepsy center for possible surgical treatment and investigational drug studies should be considered for intractable cases 6
• The goals of treatment should be to render the patient free of seizures and to allow the patient to become a participating and productive member of society 6