What are the differential diagnoses for a 2-year-old girl with episodes of absence seizures?

Differential Diagnoses for Absence Seizures in a 2-Year-Old Girl

The presentation of "absence seizures" in a 2-year-old girl is highly atypical and requires immediate consideration of alternative diagnoses, as true childhood absence epilepsy (CAE) typically begins between ages 4-8 years, with peak onset around 6-7 years. 1, 2

Critical Age-Related Considerations

• True absence seizures (childhood absence epilepsy) are extremely rare before age 4 years, making this diagnosis unlikely in a 2-year-old 2
• The age of 2 years falls outside the typical 4-8 year onset window for CAE, necessitating broader differential consideration 2, 3

Primary Differential Diagnoses to Consider

1. Behavioral or Developmental Phenomena (Non-Epileptic)

• Brief staring spells in toddlers are frequently normal developmental behaviors rather than seizures, including daydreaming, inattention, or brief dissociative moments during play 1
• These episodes lack the characteristic 3-4 Hz spike-and-wave discharges on EEG that define true absence seizures 4

2. Atypical Absence Seizures (Part of Developmental Epileptic Encephalopathy)

• Atypical absences occur in children with severe epilepsies and developmental delays, often associated with other seizure types 5
• These differ from typical absences by having more gradual onset/offset, longer duration, and more prominent motor components 5
• Associated syndromes include Lennox-Gastaut syndrome or other developmental and epileptic encephalopathies 5
• EEG shows slower spike-wave complexes (1.5-2.5 Hz) rather than the 3-4 Hz pattern of typical absences 5

3. Complex Febrile Seizures

• Complex febrile seizures can present with focal features or prolonged duration in children aged 6 months to 5 years 1
• These may be mistaken for absence seizures if the fever is not immediately recognized 1
• Approximately 33% of febrile seizures are complex in nature 1

4. Focal Seizures with Impaired Awareness

• Focal seizures can present with staring and behavioral arrest that mimics absence seizures 1, 6
• These arise from networks in a single cerebral hemisphere and may have subtle focal features 6
• Structural brain lesions (tumors, malformations of cortical development, prior injury) are more commonly associated with focal seizures 7, 6

5. Metabolic or Systemic Causes

• Hypoglycemia is a critical metabolic cause that can present with altered awareness in toddlers 7
• Electrolyte abnormalities (hyponatremia, hypocalcemia, hypomagnesemia) can cause seizure-like episodes 7
• These require immediate laboratory evaluation 7

6. Structural Brain Abnormalities

• Malformations of cortical development can present with various seizure types in early childhood 7, 6
• Hypoxic-ischemic injury or perinatal stroke may manifest with seizures at this age 7
• Intracranial infections (encephalitis, meningitis) must be excluded, especially if fever is present 7

7. Neonatal-Onset Epilepsy Syndromes (if symptoms began earlier)

• If episodes actually began in the neonatal period, hypoxic-ischemic injury (most common cause, 46-65% of neonatal seizures) should be considered 7
• Intracranial hemorrhage or perinatal stroke account for 10-12% of neonatal seizures 7

Essential Diagnostic Workup

Immediate Evaluation Required:

• Video-EEG monitoring is essential to distinguish true absence seizures from other causes, as clinical observation alone is insufficient 5
• True absence seizures show characteristic 3-4 Hz generalized spike-and-wave discharges 4
• Hyperventilation during EEG precipitates absence seizures in 90% of untreated cases 4

Neuroimaging Considerations:

• MRI brain with dedicated epilepsy protocol is indicated if focal features, developmental delay, or abnormal neurological examination are present 1, 6
• MRI is rarely indicated in neurologically normal children with generalized seizures due to low yield (only 2% abnormal findings) 1, 6
• For a 2-year-old with atypical presentation, imaging is more strongly justified than in typical CAE 1

Laboratory Studies:

• Glucose, electrolytes (sodium, calcium, magnesium), and metabolic screening should be obtained 7
• Consider infectious workup if fever or systemic symptoms present 7

Critical Clinical Pitfalls

• Do not assume absence epilepsy based on age alone—the 2-year-old age makes this diagnosis highly unlikely 2, 3
• Distinguish between typical and atypical absences, as atypical forms have worse prognosis and different treatment approaches 5
• Always obtain EEG confirmation before initiating treatment, as many conditions mimic absence seizures clinically 4, 5
• Assess for developmental delays or other neurological abnormalities, which suggest atypical absences or structural causes rather than benign CAE 5
• Consider non-epileptic causes first in this age group, as behavioral staring spells are common in toddlers 1