Researchers at University of Fukui, Japan analyzed the relation between EEG abnormalities and PDD or ADHD, and assessed the clinical utility of EEG in the differential diagnosis of these disorders. The study involved 64 PDD children and 22 ADHD children with no history of epilepsy or progressive neurological or psychiatric disease. Paroxysmal discharges at the frontopolar-frontal brain regions and background EEG abnormalities were detected preferentially in the PDD group expressing persistence or hypersensitivity, whereas central-temporal discharges were detected preferentially in the ADHD group expressing impulsivity. No significant differences in the laterality of paroxysmal discharges were found between PDD and ADHD. Patients classified as inattentive subtype ADD showed no EEG abnormality. A combination of EEG abnormalities, including background abnormalities and paroxysmal discharges at Fp-F and C-T regions, might be useful diagnostic hallmarks to distinguish PDD with ADHD from ADHD alone. Dysfunction of specific brain areas associated with EEG abnormalities might explain characteristics of PDD and ADHD symptoms. 
COMMENT. The utility of the EEG in ADHD is previously documented, especially in relation to choice of medication (stimulant vs. non-stimulant) in patients with lack of awareness and transient cognitive impairment  idem . Of 624 EEG recordings in non-epileptic children evaluated for ADHD, 26% were abnormal. Of 163 abnormal recordings, 55% were focal epileptiform discharges, localized predominantly in the central region, less frequently in frontal and temporal regions, and infrequently in parietal and occipital areas; 41.7% had generalized epileptiform discharges. Hemispheres were equally affected, but in frontal areas, the left side had more frequent spikes. Only 3 patients had background slowing and 3 had focal slowing. None had a primary diagnosis of PDD.