What are the initial diagnostic tests for a patient presenting with a first seizure?

Initial Diagnostic Tests for First Seizure

For patients presenting with a first seizure, essential initial diagnostic tests include serum glucose, serum sodium, complete metabolic panel, brain imaging (preferably MRI), and EEG within 24-48 hours of the event. 1

Laboratory Tests

The following laboratory tests are recommended for all patients with first seizures:

• Essential for all patients:

  • Serum glucose
  • Serum sodium
  • Pregnancy test (for women of childbearing age)

• For patients with altered mental status:

  • Complete metabolic panel
  • Toxicology screen (especially with suspected substance use)

• For specific presentations:

  • CBC, blood cultures, lumbar puncture (if fever present)
  • Antiepileptic drug levels (if on seizure medications)
  • CK levels (after generalized tonic-clonic seizures)
  • Troponin levels (older patients with generalized tonic-clonic seizures) 1

Prolactin levels measured 10-20 minutes after the event can help differentiate epileptic seizures from psychogenic non-epileptic seizures, with high specificity but moderate sensitivity 2, 3.

Neuroimaging

• MRI is preferred over CT for first-time seizures as it is more sensitive for detecting brain abnormalities 1
• CT scan is indicated in emergency situations when:
  • Severe structural lesion is suspected
  • Etiology is unknown
  • MRI is not immediately available 2

Electroencephalography (EEG)

• Should be performed within 24 hours after a seizure, particularly in children 1, 2
• If the initial EEG during wakefulness is normal, a sleep EEG is recommended 2
• EEG helps:
  • Differentiate seizure types
  • Identify epilepsy syndromes
  • Predict recurrence risk 1

Lumbar Puncture

• Not routinely indicated for all first seizures
• Recommended only when cerebral infection is suspected
• Exception: Should be considered in infants less than six months of age 2

Clinical Correlation

Laboratory abnormalities are common in patients with seizures:

• Sodium abnormalities: found in 34.8% of patients
• Glucose abnormalities: found in 52.3% of patients
• Potassium abnormalities: found in 6.7% of patients
• Calcium abnormalities: found in 6.2% of patients 4

Important Considerations

• Seizures may be provoked by correctable factors including organ failure, electrolyte imbalance, medication effects, or medication withdrawal 5
• Approximately 10% of the population will have one or more seizures during their lifetime, but not all will develop epilepsy 6
• Identifying the seizure type and potential epilepsy syndrome guides diagnostic testing and treatment decisions 6

Common Pitfalls to Avoid

1. Failure to obtain appropriate neuroimaging: Brain imaging is essential for first-time seizures to identify structural abnormalities.

2. Delayed EEG: EEG should be performed within 24-48 hours of the seizure when possible, as the yield decreases with time.

3. Overreliance on CT: While CT may be used in emergency settings, MRI is more sensitive for detecting epileptogenic lesions.

4. Missing correctable causes: Always evaluate for potentially reversible causes of seizures (metabolic, toxic, infectious).

5. Unnecessary lumbar puncture: Reserve this for cases with suspected CNS infection or in infants under 6 months.

By following this systematic diagnostic approach, clinicians can effectively evaluate patients presenting with first seizures and guide appropriate management decisions.