If untreated, various neurological complications including seizures or coma may occur, as BCAAs, especially leucine, are cytotoxic to brain cells, leading to cytotoxic brain edema affecting the myelinated white matter as was seen in the diffusion-weighted imaging (DWI) of our patient. It is characterized by an enzymatic deficiency of branched-chain alpha-ketoacid dehydrogenase complex leading to accumulation of BCAAs (leucine, isoleucine, and valine), and their toxic by-products (keto acids) in blood and urine.Ībnormal accumulation of these amino acids results in a variety of symptoms including lethargy, irritability, feeding problems, vomiting, and the characteristic maple-syrup odor of urine. The condition gets its name from the characteristic maple-syrup odor of the affected infant's urine. It has an annual incidence of 1 in 180,000 live births, with a higher prevalence in Amish, Mennonite, and Jewish children. MSUD, also known as branched-chain ketoaciduria, is a rare autosomal-recessive disorder of BCAA metabolism. Extensive bilateral T2/Fluid-attenuated inversion recovery white matter hyperintensity was also noted. MRI was obtained and showed restricted diffusion involving the corticospinal tracts, thalami, globus palladi, midbrain, dorsal brain stem, and cerebellar white matter. Laboratory testing revealed metabolic acidosis (serum HCO 3 = 14 mmol/L), ketosis (urine ketones >80 mg/dL), and mild hyperammonemia (serum NH 3 = 83 µmol/L). On physical examination, he was found to be normothermic, normotensive, and with stable vital signs. He did not have any evidence of overt obtundation or emesis. The patient was thereafter admitted to our hospital where he exhibited irritability, hypertonicity, high-pitched cry, and sleepiness. Confirmatory testing done with plasma amino acid levels collected at 8 days of life showed elevated levels of leucine. The patient's newborn screenings were abnormal, showing elevated BCAAs. The patient presented with slight irritability and poor feeding in the second week of life. A 2-week-old male infant was born at term after an uneventful pregnancy and a normal vaginal delivery.
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