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PubMed This is a summary of 13 peer-reviewed journal articles Updated

Getting the Right Diagnosis: The Role of the EEG

At a Glance

An EEG is the gold standard for diagnosing Childhood Absence Epilepsy (CAE). Doctors look for a specific 3 Hz spike-and-wave pattern during the test, often triggering a brief staring spell using hyperventilation (like blowing on a pinwheel) to confirm the diagnosis and tailor treatment.

Confirming a diagnosis of Childhood Absence Epilepsy (CAE) is a specialized process that moves beyond simple observation. While you may have seen your child stare into space, doctors use specific tests—primarily the Electroencephalogram (EEG)—to look for the brain’s unique electrical “fingerprint” that defines this condition [1].

The Role of the EEG

An EEG measures the electrical activity of the brain using small sensors attached to the scalp. In CAE, the brain’s activity is typically normal between seizures. However, during an absence seizure, the EEG shows a very specific pattern: the 3 Hz spike-and-wave discharge [2].

  • Spike: A sharp, fast electrical discharge.
  • Wave: A slower, rounded electrical discharge.
  • 3 Hz (Hertz): This means the spike-and-wave cycle repeats exactly three times per second.

This 3 Hz pattern is the “gold standard” for diagnosing CAE. If the pattern is much slower (e.g., 2 Hz) or faster, or if it includes polyspikes (multiple spikes in a row), it may point to a different, sometimes more complex, type of epilepsy [3][4].

The Pinwheel Test (Hyperventilation)

One of the most reliable ways to confirm CAE in a doctor’s office is through hyperventilation. You may see the doctor or technician ask your child to blow on a pinwheel or a piece of paper for three minutes [5].

  • Why it works: Deep, rapid breathing changes the levels of carbon dioxide in the blood, which can trigger an absence seizure in children with CAE [6][7].
  • The benefit: This allows the medical team to see the seizure happen in real-time while simultaneously recording the 3 Hz pattern on the EEG, providing a definitive diagnosis [5].

Differentiating the Absence Syndromes

Not all staring spells are the same. Doctors use your child’s age and the specific EEG patterns to distinguish between three main syndromes:

Syndrome Typical Age of Onset Key Differences
Early Onset Absence Epilepsy (EOAE) Under 4 years old Often linked to specific genetic mutations (like SLC2A1). May involve motor symptoms like stumbling or shaking [8][9].
Childhood Absence Epilepsy (CAE) 4 to 10 years old The “classic” form. Characterized by the 3 Hz spike-and-wave pattern and a high rate of outgrowing the condition [1][10].
Juvenile Absence Epilepsy (JAE) 10 to 17 years old Seizures often last longer and are less frequent than in CAE. There is a higher risk of developing “grand mal” (tonic-clonic) seizures later in life [11][12].

Why the Specific Label Matters

Getting the right diagnosis—distinguishing CAE from JAE or EOAE—is critical because it changes the treatment plan and the long-term outlook. For example, if a child is diagnosed with Early Onset Absence, the doctor might test for GLUT1 Deficiency Syndrome, which is treated with a specialized diet rather than standard seizure medications [9][13]. Similarly, children with JAE may need medication for a longer period than those with CAE [11]. Through a combination of age-tracking and EEG patterns, your medical team can build a roadmap tailored to your child’s specific needs.

Common questions in this guide

What does a 3 Hz spike-and-wave pattern mean on an EEG?
A 3 Hz spike-and-wave pattern is the classic electrical signature of Childhood Absence Epilepsy. It means the brain's electrical activity repeats a sharp spike and a rounded wave exactly three times per second during a seizure.
Why does the doctor ask my child to blow on a pinwheel during an EEG?
Blowing on a pinwheel is a hyperventilation test used to safely trigger an absence seizure in the doctor's office. Deep, rapid breathing changes carbon dioxide levels in the blood, allowing the medical team to record the seizure on the EEG in real-time.
How do doctors tell the difference between Childhood and Juvenile Absence Epilepsy?
Doctors differentiate these syndromes based primarily on the child's age when the seizures start and specific patterns on their EEG. Juvenile Absence Epilepsy typically begins between ages 10 and 17, and the seizures may last longer than those in the childhood form.
What are polyspikes on an EEG report?
Polyspikes are multiple sharp electrical discharges in a row seen on an EEG recording. If polyspikes are present or the brainwave pattern is significantly faster or slower than 3 Hz, it may indicate a different or more complex type of epilepsy that requires a different treatment approach.
Why would my child need genetic testing for absence seizures?
If your child began having staring spells before the age of 4, they may be diagnosed with Early Onset Absence Epilepsy. In these cases, doctors often recommend genetic testing for the SLC2A1 gene to check for GLUT1 Deficiency Syndrome, which is treated with a specialized diet.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.My child's EEG showed the '3 Hz spike-and-wave' pattern—is it exactly 3 Hz, or is it faster or slower, and what does that mean for their diagnosis?
  2. 2.During the EEG, were any 'polyspikes' seen, and does that change the likelihood of the first medication being successful?
  3. 3.Based on my child's age of onset and their EEG, are you diagnosing them with CAE or a different syndrome like Juvenile Absence Epilepsy?
  4. 4.If the initial hyperventilation test didn't trigger a seizure, does that mean my child might not have CAE?
  5. 5.Are there any genetic tests you recommend, specifically looking for the SLC2A1 gene, given my child's age or symptoms?

Questions For You

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References

References (13)
  1. 1

    ILAE definition of the Idiopathic Generalized Epilepsy Syndromes: Position statement by the ILAE Task Force on Nosology and Definitions.

    Hirsch E, French J, Scheffer IE, et al.

    Epilepsia 2022; (63(6)):1475-1499 doi:10.1111/epi.17236.

    PMID: 35503716
  2. 2

    Absence seizures during sleep in childhood absence epilepsy: A sign of drug resistance?

    Chen J, Liu P, Hu W, Shi K

    Brain & development 2022; (44(4)):313-317 doi:10.1016/j.braindev.2021.11.008.

    PMID: 34895931
  3. 3

    Electroclinical features and long-term therapeutic response in patients with typical absence seizures.

    Vlachou M, Skrimpas GA, Kural MA, et al.

    Epileptic disorders : international epilepsy journal with videotape 2022; (24(2)):315-322 doi:10.1684/epd.2021.1392.

    PMID: 34859792
  4. 4

    A systematic review of electroencephalographic findings in Lennox-Gastaut syndrome.

    Nizami FM, Trivedi S, Kalita J

    Epilepsy research 2024; (205()):107406 doi:10.1016/j.eplepsyres.2024.107406.

    PMID: 38976954
  5. 5

    A Review of Hyperventilation Activation in Diagnosis and Management of Childhood Absence Epilepsy.

    Rao CK, Kuperman R

    Journal of child neurology 2024; (39(11-12)):425-432 doi:10.1177/08830738241273347.

    PMID: 39175400
  6. 6

    Diagnosing and managing childhood absence epilepsy by telemedicine.

    Stafstrom CE, Sun LR, Kossoff EH, et al.

    Epilepsy & behavior : E&B 2021; (115()):107404 doi:10.1016/j.yebeh.2020.107404.

    PMID: 33323339
  7. 7

    Respiratory alkalosis provokes spike-wave discharges in seizure-prone rats.

    Salvati KA, Souza GMPR, Lu AC, et al.

    eLife 2022; (11()).

    PMID: 34982032
  8. 8

    Clinical, etiological, and therapeutic profile of early-onset absence seizures: A case series analysis.

    Bergonzini P, Caramaschi E, Spallino A, et al.

    Clinical neurology and neurosurgery 2025; (249()):108673 doi:10.1016/j.clineuro.2024.108673.

    PMID: 39662378
  9. 9

    Rare and Treatable Cause of Early-Onset Refractory Absence Seizures.

    Panandikar GA, Ravat SH, Ansari RR, Desai KM

    Journal of pediatric neurosciences 2018; (13(3)):358-361 doi:10.4103/JPN.JPN_146_17.

    PMID: 30271476
  10. 10

    Long-term prognosis of childhood absence epilepsy.

    Martínez-Ferrández C, Martínez-Salcedo E, Casas-Fernández C, et al.

    Neurologia 2019; (34(4)):224-228 doi:10.1016/j.nrl.2016.12.005.

    PMID: 28325560
  11. 11

    Changes in awake and sleep electroencephalography characteristics after 1-year treatment for childhood and juvenile absence epilepsy.

    Edizer S, Baysal BT, Ünalp A, Yılmaz Ü

    Seizure 2023; (110()):244-252 doi:10.1016/j.seizure.2023.06.023.

    PMID: 37441906
  12. 12

    Unsupervised clustering of a deeply phenotyped cohort of adults with idiopathic generalized epilepsy.

    Gavnholt L, Gesche J, Cerulli Irelli E, et al.

    Epilepsia 2025; (66(3)):700-711 doi:10.1111/epi.18225.

    PMID: 39724391
  13. 13

    Glut1 deficiency syndrome: Absence epilepsy and La Soupe du Jour.

    Thouin A, Crompton DE

    Practical neurology 2016; (16(1)):50-2 doi:10.1136/practneurol-2015-001194.

    PMID: 26336901

This page explains the diagnostic process and EEG testing for Childhood Absence Epilepsy for educational purposes. Always consult a pediatric neurologist to interpret your child's specific EEG results and symptoms.

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