What is the initial approach to a two-year-old girl presenting with absence seizures?

Typical Presentation of Absence Seizures in a Two-Year-Old Girl

Absence seizures presenting at age 2 years would be highly atypical and should prompt consideration of alternative diagnoses or atypical absence seizures associated with severe epilepsy syndromes, as typical childhood absence epilepsy characteristically begins later in childhood (usually between ages 4-8 years).

Age-Related Concerns with This Presentation

• Typical absence seizures (childhood absence epilepsy) do not usually start at age 2 years 1, 2
• At this young age, what appears to be absence seizures is more likely to represent:
  • Atypical absence seizures associated with developmental and epileptic encephalopathies, which affect children with severe epilepsies and learning difficulties along with other seizure types 3
  • Complex partial seizures (focal seizures with impaired awareness), which can mimic absence seizures with staring and unresponsiveness 4
  • Other causes of staring episodes that must be ruled out 4

Clinical Features to Distinguish Seizure Types

If These Were Typical Absences (Unlikely at Age 2):

• Brief (seconds) generalized seizures with sudden onset and termination 1
• Impairment of consciousness (the "absence") 1
• Often associated with myoclonia, mainly of facial muscles 1
• Easily precipitated by hyperventilation in about 90% of untreated patients 1
• May be spontaneous or triggered by photic stimuli, pattern, video games, or emotional factors 1

If These Are Atypical Absences (More Likely at Age 2):

• Associated with severe epilepsies and learning difficulties 3
• Usually occur along with other seizure types 3
• Typically intractable and persist lifelong 3
• Prognosis depends on underlying etiology or associated epilepsy syndrome 3

Initial Diagnostic Approach

Essential Diagnostic Testing:

• EEG is recommended as part of the neurodiagnostic evaluation of a child with an apparent first unprovoked seizure 5
• Video-EEG is essential for diagnosis of atypical absences 3
• Typical absences show generalized 3 to 4Hz spike/polyspike and slow wave discharges on EEG 1

Neuroimaging Considerations:

• MRI is the preferred imaging modality if neuroimaging is obtained 5
• Nonurgent MRI should be seriously considered in children aged <1 year with first seizure 5
• For a 2-year-old, MRI should be considered given the atypical age and to evaluate for structural causes 5, 6
• MRI is superior to CT in detecting brain abnormalities and should be the primary imaging modality for newly diagnosed seizures 5, 6

Laboratory Studies:

• Laboratory tests should be ordered based on individual clinical circumstances including suggestive findings such as vomiting, diarrhea, dehydration, or failure to return to baseline alertness 5

Critical Pitfalls to Avoid

• Do not assume typical childhood absence epilepsy at age 2 years - this diagnosis is age-inappropriate 1, 2
• Do not confuse complex partial seizures with absence seizures - episodes of staring and unresponsiveness due to nonepileptic causes must be ruled out, and the treatment strategy and prognosis are very different 4
• Do not rely on clinical observation alone - 24-hour EEG reveals spike-and-wave episodes in higher frequency than absences reported by parents 7
• Do not use CT instead of MRI - CT is inadequate for brain imaging in the evaluation of children with seizures 4

Treatment Implications

• If confirmed as atypical absences: Usually intractable and require polytherapy, although typically with limited efficacy 3
• Epilepsy syndromes featuring atypical absences require a multidisciplinary approach 3
• If typical absences were confirmed (despite atypical age): First-line options include valproic acid, ethosuximide, or lamotrigine 1, though valproate controls absences in 75% of patients and also controls other generalized seizure types 1