Introduction: Several studies have shown an increased prevalence of epilepsy in children with autism spectrum disorders (ASD), especially in autistic regression (AR), in which epilepsy has been pointed as a possible causal factor. A heterogeneous group of etiologies has been described in ASD, many of them common to epilepsy. The aim of this study is to analyze the relationship between AR and epilepsy or electroencephalogram (EEG) epileptiform abnormalities.

Methods: We describe 70 patients diagnosed AR, with a follow-up period of 1-19 years. All patients underwent EEG at the time of diagnosis and during the follow-up, cerebral MRI, metabolic screening and genetic studies.

Results: Among the 70 children, an underlying etiology was found in 32 (45,3%) whereas the other 38 (54,3%) were consider cryptogenic. In the entire AR cohort, the prevalence of epilepsy was 52,9%, compared with 93,7% in the syndromic group and 18,4% in the cryptogenic group. The proportion of epileptiform EEGs in the whole group was 55,7%, compared with 96,9% in the syndromic group and 21,1% in the cyptogenic group. Regression was preceded by epilepsy in 20 patients (28,6%) and by epileptiform EEG in 25 (35,7%), all of them in the syndromic group.

Conclusions: The prevalence of epilepsy and EEG epileptiform abnormalities is much higher in syndromic AR than in cryptogenic AR. In our cohort, epilepsy preceded the regression only in syndromic AR patients. This suggests the existence of a common pathophysiological mechanism for AR and epilepsy, replacing the concept of epilepsy as a causal factor in autism.