EEG pattern in phenylketonuria under early initiated dietary treatment.

Nineteen of 161 infants with a confirmed diagnosis of phenylketonuria (PKU) had initially abnormal EEGs obtained within days of diagnosis. The abnormalities consisted of single repetitive or multiple spikes and/or sharp waves, focal or scattered, which rarely occurred in paroxysmal bursts. Initial maximal diagnostic serum phenylalanine (Phe) levels were significantly higher for the group with abnormal EEGs. The mean diagnostic serum Phe level was 56 mg/dL in the group with abnormal EEGs, whereas the mean diagnostic Phe level was 48 mg/dL in the group with normal tracings. The average age at initiation of restrictive dietary treatment was approximately 3 weeks. The initially abnormal EEGs became normal by 1 year of age in all but two patients who had a minimal and a mild abnormality, respectively. Hypsarrhythmic patterns were not seen. Infants with PKU detected early and treated well do not appear to need routine EEG monitoring.