A fluctuation of serum osmolality inducing osmotic demyelination syndrome.

Osmotic demyelination syndrome (ODS) is an uncommon acute demyelinating process which involves the central nervous system. Rapid correction of chronic hyponatremia with increasing serum osmolality is the most common cause of ODS. We report the first case of an infant with moderate dehydration and initially normal serum Na who developed ODS associated with a fluctuation of serum osmolality. We present the lowest decreasing rate of serum Na level ever reported causing ODS. The fluctuation of serum osmolality in this case expands the list of precipitating causes of ODS in children. The case also highlights the appropriate intravenous fluid for initial rehydration in infant.