Expanding the Spectrum of Methylmalonic Acid-Induced Pallidal Stroke: First Reported Case of Metabolic Globus Pallidus Stroke in Transcobalamin II Deficiency

A 10-year-old boy with transcobalamin II (TCII) deficiency on oral cyanocobalamin therapy presented with acute right hemiparesis and sensory axonal neuropathy in the context of an intercurrent viral illness. MRI demonstrated unilateral globus pallidus stroke with normal MRA. Echocardiogram was normal. Methylmalonic acid in serum was mildly elevated at 10.29 μmol/L (normal < 0.37 μmol/L), which was an 18-fold increase from his previous baseline. The patient was switched to IM cyanocobalamin and serum methylmalonic acid levels normalized over 6 months to 0.01 μmol/L. After 4 months of IM cyanocobalamin therapy, the neuropathy had resolved. Repeat MRI 4 months after the sentinel stroke demonstrated a chronic-appearing contralateral globus pallidus stroke of uncertain timing.