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.

Keywords: Osmotic demyelination syndrome, Infant, Central nervous system, Diarrhea