EEG in assessing hydroxycobalamin therapy in neonatal methylmalonic aciduria with homocystinuria

We performed serial electroencephalograms (EEG) in a newborn with methylmalonic aciduria and homocystinuria to assess the effects of hydroxycobalamin (OHcbl) therapy on the CNS. Diagnosis was made at 22 days of age: she had torpor, failure to thrive and hypotonia of the limbs, and intermittent opisthotonus. The first EEG, performed on the first day of therapy, showed abnormal and immature transients, low voltage and very long flat periods in the discontinuous part of the tracing. These features quickly improved during therapy. After 13 days of OHcbl therapy, the EEG tracing became normal for conceptional age and showed normal sleep phases with only minor anomalies; only mild hypotonia still remained and biochemical parameters normalized. The decrease in blood homocysteine (index of blood detoxification) was statistically correlated to the reduction of the length of flat periods in EEG (p < 0.01). In conclusion, changes in neonatal EEG, particularly the length of interburst periods in the intermittent part of the tracing, appeared to be a reliable index for evaluating drug effectiveness in methylmalonic aciduria and homocystinuria.