To investigate the clinical characteristics of late-onset epilepsy combined with autism spectrum disorder (ASD), and the relationship between certain types of electroencephalography (EEG) abnormalities in ASD and associated neuropsychological problems.

Thirty patients diagnosed with ASD in early childhood and later developed clinical seizures were reviewed retrospectively. First, the clinical characteristics, language and behavioral regression, and EEG findings of these late-onset epilepsy patients with ASD were investigated. The patients were then classified into 2 groups according to the severity of the EEG abnormalities in the background rhythm and paroxysmal discharges. In the severe group, EEG showed persistent asymmetry, slow and disorganized background rhythms, and continuous sharp and slow waves during slow sleep (CSWS).

Between the two groups, there was no statistically significant difference in mean age ( P =0.259), age of epilepsy diagnosis ( P =0.237), associated family history ( P =0.074), and positive abnormal magnetic resonance image (MRI) findings ( P =0.084). The severe EEG group tended to have more neuropsychological problems ( P =0.074). The severe group statistically showed more electrographic seizures in EEG ( P =0.000). Rett syndrome was correlated with more severe EEG abnormalities ( P =0.002). Although formal cognitive function tests were not performed, the parents reported an improvement in neuropsychological function on the follow up checkup according to a parent's questionnaire.

Although some ASD patients with late-onset epilepsy showed severe EEG abnormalities, including CSWS, they generally showed an improvement in EEG and clinical symptoms in the long-term follow up. In addition, severe EEG abnormalities tended to be related to the neuropsychological function.