What are the criteria for diagnosing epilepsy?

Criteria for Diagnosing Epilepsy

Epilepsy is diagnosed when a patient meets any of the following criteria: (1) at least two unprovoked seizures occurring more than 24 hours apart; (2) one unprovoked seizure with a high probability (≥60%) of recurrence over the next 10 years; or (3) diagnosis of a specific epilepsy syndrome. 1

Core Diagnostic Criteria

• Epilepsy is defined as a disorder of the brain characterized by an enduring predisposition to generate epileptic seizures 1
• The traditional definition requiring two unprovoked seizures has been expanded to include situations with high recurrence risk after a single seizure 1
• Epilepsy is considered "resolved" in individuals who have remained seizure-free for 10 years and off antiseizure medications for at least 5 years 1
• Approximately 10% of the population will experience at least one seizure during their lifetime, but only 1-3% develop epilepsy 2

Diagnostic Approach

Clinical Assessment

• Detailed seizure history is essential, focusing on seizure characteristics, duration, precipitating factors, and post-ictal state 3
• Differentiation between provoked seizures (occurring in acute illness) and unprovoked seizures (epilepsy) is crucial 2
• Common conditions that mimic seizures must be excluded: pseudoseizures, syncope, migraine, cerebrovascular events, movement disorders, and sleep disorders 2

Seizure Classification

• Classification of seizure type guides identification of the brain region where the seizure originated 2
• Seizures are broadly categorized as:
  • Focal seizures (originating in one hemisphere) 4
  • Generalized seizures (involving both hemispheres) 4
  • Combined focal and generalized seizures 4
  • Unknown onset seizures 4

Epilepsy Syndrome Classification

• Epilepsy syndromes are defined by multiple factors including seizure type, age of onset, family history, and findings on examination and diagnostic studies 2
• Identifying the specific epilepsy syndrome provides insight into natural history, prognosis, and appropriate therapy 2

Diagnostic Testing

Electroencephalography (EEG)

• EEG is recommended as part of the neurodiagnostic evaluation for all patients with apparent first unprovoked seizure 4
• EEG can help identify epileptiform abnormalities that increase risk of seizure recurrence 4
• Video EEG monitoring may be necessary to capture and characterize events when diagnosis is uncertain 2

Neuroimaging

• MRI is the preferred imaging modality for non-emergent evaluation of seizures 5, 4

  • Superior sensitivity (detects up to 55% of abnormalities vs. 18-30% with CT) 5
  • Better visualization of hippocampal abnormalities, cortical dysplasias, and subtle structural lesions 5
  • Should be performed using dedicated epilepsy protocols with 3T scanners when possible 4, 5

• CT head imaging is appropriate in emergent situations 5, 4:

  • When rapid assessment is needed for immediate intervention 5
  • Patient requires ready access during scanning 5
  • Acute trauma is suspected 5
  • Patient is unstable or requires close monitoring 5

• Dedicated MRI seizure protocol should include 5:

  • Coronal T1-weighted imaging (3mm) perpendicular to the hippocampus 5
  • High-resolution 3D T1-weighted gradient echo with 1mm isotropic voxels 5
  • Coronal T2-weighted sequences 5
  • Coronal and axial (or 3D) fluid-attenuated inversion recovery (FLAIR) sequences 5

Advanced Imaging

• FDG-PET/CT may be complementary when MRI is normal but seizures persist 5

  • Sensitivity of 87-90% for temporal lobe epilepsy 5
  • Sensitivity of 38-55% for extra-temporal lobe epilepsy 5

• SPECT may be useful in presurgical planning 5

  • Provides assessment of regional cerebral blood flow 5
  • Statistical ictal SPECT co-registered to MRI can identify hyperperfusion focus in 84% of patients 5

Laboratory Testing

• Laboratory tests should be ordered based on individual clinical circumstances 4
• Consider tests for metabolic disturbances, particularly when there are suggestive clinical findings 4
• Toxicology screening should be considered across all age groups if drug exposure or substance abuse is suspected 4

Special Considerations

Pediatric Patients

• In children with first non-febrile seizure, lumbar puncture is of limited value and should be used primarily when meningitis or encephalitis is suspected 4
• Emergent neuroimaging should be performed in a child who exhibits a postictal focal deficit that does not quickly resolve 4
• MRI is rarely indicated in neurologically normal children presenting with typical generalized seizures due to their likely genetic underpinnings 4

High-Risk Indicators

• Prioritize imaging for patients with 5, 4:
  • Focal neurological deficits on examination 5
  • Persistent headache 5
  • Recent history of head trauma 5
  • Abnormal EEG findings 5
  • Focal seizure features 5

Common Pitfalls to Avoid

• Assuming a normal CT excludes structural abnormality - MRI may still reveal significant pathology 5
• Delaying appropriate EEG, which may be more informative than CT for certain seizure types 5
• Failing to distinguish between provoked seizures (which don't require antiseizure medications) and unprovoked seizures (which may require treatment) 2