BLOG SERIES: " What Your Child's EEG Really Means" — Post 2 of 6

BLOG SERIES: "What Your Child's EEG Really Means" — Post 2 of 6

How Common Are Abnormal EEGs? The Numbers by Diagnosis

One of the most reassuring things a pediatric neurologist can tell a family is also one of the most counterintuitive: abnormal EEG findings are extremely common in children with neurodevelopmental conditions — and in most cases, they do not mean epilepsy is coming.

Here is what the published research actually shows, broken down by diagnosis.

Rate of abnormal EEG by diagnosis. But what does that mean?

Healthy Children: 1–4%

In neurologically typical children with no history of seizures or neurological diagnosis, epileptiform discharges on routine EEG appear in roughly 1–4% of recordings. Most of these are centrotemporal (Rolandic) spikes or generalized spike-wave discharges — patterns that are well-known to be largely benign in childhood and that typically resolve without treatment.

Long-term follow-up studies are reassuring: the large majority of these children never develop clinical epilepsy, and many of the discharges disappear spontaneously by adolescence.

ADHD: ~50%

This number surprises most families — and many clinicians. In a prospective Norwegian cohort study of 517 children ages 6–14 with ADHD, 52.8% had EEG abnormalities on routine awake recording. Non-epileptiform changes (slowing, asymmetry) accounted for the majority, but epileptiform discharges were identified in roughly 7–8% of the total group.

A separate Japanese cohort found approximately 48% of ADHD children had abnormal EEGs, with 22% showing epileptiform discharges. Importantly, over a three-year follow-up, these findings did not significantly predict new clinical seizures.

Autism Spectrum Disorder: 12–78%

ASD shows the widest range of any group — and for a methodologically important reason. A brief routine awake EEG captures a much narrower window than a prolonged study that includes sleep. Studies consistently show:

•       Routine awake EEG: approximately 12–30% abnormality rate in seizure-free children with ASD

•       24-hour ambulatory with sleep: rates rise to 40–60%

•       Prolonged polysomnographic recording: rates of up to 78% have been reported

This variability is not noise — it reflects the well-established principle that epileptiform discharges in ASD are strongly activated by sleep, particularly in NREM. A routine EEG that misses sleep is likely to underestimate the true burden of EEG abnormality in this population.

A "normal" EEG in a child with ASD who has not had a sleep recording may not be as reassuring as it sounds.

Cerebral Palsy: ~65–76%

Children with cerebral palsy carry the highest burden of EEG abnormalities across all neurodevelopmental groups. In the landmark Zafeiriou study of 151 CP patients, among those with no history of clinical seizures, 76% had abnormal EEGs. Of those, epileptiform activity was found in 38.6% and generalized slow waves in another 40%. Only about a third of seizure-free CP patients had entirely normal recordings.

Summary Table

Population	Abnormal EEG Rate (No Seizures)	Recording Type
Healthy children	1–4%	Routine awake
ADHD	~50%	Routine awake
Autism Spectrum Disorder	12–78%	Routine to prolonged sleep
Cerebral Palsy	~65–76%	Routine

References

1.     Socanski D, et al. EEG abnormalities in children with ADHD and risk of epileptic seizures: 3-year follow-up. Annals of General Psychiatry. 2024. https://annals-general-psychiatry.biomedcentral.com/articles/10.1186/s12991-024-00510-4

2.     Bruni O, et al. EEG Features in Autism Spectrum Disorder: A Retrospective Analysis in Preschoolers. J Clin Med. 2023. https://pmc.ncbi.nlm.nih.gov/articles/PMC9954463/

3.     Lesca G, et al. EEG Abnormalities and Phenotypic Correlates in ASD Preschoolers. J Clin Med. 2025;14(2):529. https://pmc.ncbi.nlm.nih.gov/articles/PMC11766335/

4.     Zafeiriou DI, et al. Electroencephalographic findings in children with cerebral palsy. Pediatric Neurology. 2002. https://pubmed.ncbi.nlm.nih.gov/11853323/

5.     Maximo JO, et al. Electroencephalographic Abnormalities in ASD: Characteristics and Therapeutic Implications. Medicina. 2020. https://www.mdpi.com/1648-9144/56/9/419

➡ Up next: Post 3 addresses the question families really want answered: does an abnormal EEG mean my child will develop epilepsy?