What are focal seizures?

Focal Seizures: Definition, Classification, and Clinical Presentation

Focal seizures are seizures that arise within networks of a single cerebral hemisphere and may remain localized or subsequently become more widely distributed. 1

Definition and Classification

• Focal seizures originate in a specific area of the brain, affecting only one hemisphere initially, though they may spread to become more widely distributed 1
• They are part of the International League Against Epilepsy's (ILAE) operational classification system, which was last revised in 2017 1
• Focal seizures can be further categorized based on:
  • Awareness level: focal aware seizures (retained awareness) or focal impaired awareness seizures (formerly known as complex partial seizures) 1
  • Symptom type: motor onset or non-motor onset 1, 2
  • Progression: may remain localized or evolve to bilateral tonic-clonic seizures 3

Clinical Presentation

Motor Symptoms

• Motor manifestations can include:
  • Jerking of one extremity or one side of the body 1
  • Abnormal facial movements 1
  • Small repetitive movements 1
  • Automatisms (automatic, repetitive movements) 2
  • Atonic (sudden loss of muscle tone), clonic (rhythmic jerking), tonic (muscle stiffening) movements 2
  • Epileptic spasms, hyperkinetic or myoclonic movements 2

Non-Motor Symptoms

• Non-motor manifestations can include:
  • Staring spells (focal impaired awareness) 1
  • Autonomic symptoms (e.g., sweating, chills, cardiovascular changes) 2, 4
  • Behavior arrest 2
  • Cognitive changes (e.g., déjà vu, jamais vu) 2
  • Emotional alterations 2
  • Sensory phenomena (e.g., tingling, unusual smells or tastes) 2

Epidemiology and Significance

• Focal seizures represent the most common seizure type in both children and adults 5, 3
• Focal epilepsies account for the majority of epilepsy cases across age groups 3
• The frequency of recurrence of focal seizures can be up to 94%, which is considerably higher than that for generalized seizures (72%) 1

Etiology

• In children, focal epilepsies typically fall into three groups:
  • Self-limited focal epilepsy syndromes (e.g., self-limited epilepsy with centrotemporal spikes) 3
  • Focal epilepsy of unknown cause 3
  • Focal epilepsy of known cause (e.g., structural lesions - developmental or acquired) 3
• In adults, focal epilepsies are often acquired and may be caused by:
  • Structural lesions such as stroke, infection, traumatic brain injury 3
  • Brain tumors, vascular malformations 3
  • Metabolic disorders, autoimmune conditions 3
  • Genetic causes 3

Diagnostic Approach

• Diagnosis relies on:

  • Detailed history from patient and eyewitnesses 6
  • Electroencephalography (EEG) 6, 3
  • Neuroimaging: MRI is more sensitive than CT for detecting brain abnormalities 1, 6
  • Video EEG to record ictal events may be necessary in some cases 6

• MRI findings in focal seizures:

  • Can detect developmental abnormalities, hemorrhage, neoplasm, and gliosis 1
  • Shows focal brain abnormalities in up to 55% of children with seizures (compared to 18% with CT) 1
  • Requires optimized epilepsy protocol with adequate spatial resolution and multiplanar reformatting 1

First Aid Management

• First aid providers should:
  • Activate EMS for first-time seizures, seizures lasting >5 minutes, multiple seizures without return to baseline, or seizures with complications 1
  • Minimize risk of injury by helping the person to the ground, placing them in recovery position, and clearing the area around them 1
  • Stay with the person having a seizure 1
  • Avoid restraining the person or putting anything in their mouth 1

Common Pitfalls and Caveats

• Focal seizures can be misdiagnosed due to their diverse clinical presentations, especially non-motor symptoms 4
• Some focal seizure syndromes (e.g., benign rolandic seizures, benign occipital epilepsy) can be diagnosed clinically or through specific EEG patterns and may not require imaging 1
• Routine MRI protocols may miss epileptogenic lesions; specialized epilepsy protocols are often needed 1
• Patients with drug-resistant focal epilepsy should be promptly referred to an epilepsy center for comprehensive evaluation and consideration for surgical treatment 3