A 7-day-old girl had an elevated
leucine level on newborn screen drawn at 2 days of age and was suspected of having
maple syrup urine disease (MSUD). When reported, the patient was immediately admitted to hospital, and started on a modified diet involving high calories with reduced
branched chain amino acid (BCAA) formula. Clinical exam was normal at initial assessment. Despite rapid initiation of treatment, the baby became lethargic and somnolent over the next day. Diet was stopped and infusions of 12.5%
dextrose and 20% intravenous
lipids at 2 g/kg per day were immediately started.
Lethargy improved within 3 h of intravenous
therapy initiation. Brain magnetic resonance imaging demonstrated diffuse
cerebral edema, and symmetric restricted diffusion in bilateral cerebellar white matter, dorsal brainstem, thalami, globi pallidi, posterior limbs of internal capsules, and corona radiata. Plasma
leucine was 1.98 mmol/L on admission (normal 0.05-0.17 mmol/L), decreasing to 1.34 mmol/L with diet, however
clinical deterioration occurred despite improving
leucine levels.Cerebral
edema in MSUD is thought secondary to a combination of increased cerebral BCAA levels, and depleted levels of other
essential amino acids, as well as
neurotransmitters. Our case illustrates that newborns can develop
encephalopathy with
cerebral edema despite treatment with special formula initiated while asymptomatic. These findings suggest decompensation may begin early on, so that early introduction of high
dextrose infusion and intravenous
lipids, in combination with reduced BCAA formula, should be initiated for any patient with a positive newborn screen for MSUD.