Extrapontine myelinolysis resulting in transient cortical blindness.

Central pontine myelinolysis and extrapontine myelinolysis are characterized by symmetric demyelination subsequent to rapid shifts in serum osmolality. Described here is a novel case of transient cortical blindness in association with imaging features of extrapontine myelinolysis, which occurred in a child with carbamoyl phosphate synthetase deficiency after rapid correction of hyperammonemia. Serum sodium levels were within normal limits at presentation and throughout the period of ammonia correction. A potential pathogenic mechanism of osmotic demyelination in the setting of acute treatment for hyperammonemia in a patient with a urea cycle abnormality includes disruption of the blood-brain barrier and re-equilibration of organic osmolytes, particularly glutamine.