Osmotic demyelination syndrome following slow correction of hyponatraemia

Hyponatraemia is the most common electrolyte disturbance observed in hospital inpatients. We report a 90-year-old woman admitted generally unwell following a fall with marked confusion. Examination revealed a tender suprapubic region, and investigations observed elevated inflammatory markers and bacteriuria. Admission investigations demonstrated a serum sodium of 110 mmol/L with associated serum osmolality 236 mmol/kg and urine osmolality 346 mmol/kg. She was treated for hyponatraemia secondary to syndrome of inappropriate antidiuretic hormone (SIADH) and urosepsis. However, her serum sodium failed to normalise despite fluid restriction, necessitating treatment with demeclocycline and hypertonic saline. Despite slow reversal of hyponatraemia over 1 month, the patient developed generalised seizures with pontine and thalamic changes on MRI consistent with osmotic demyelination syndrome (ODS). This case highlights the risk of ODS, a rare but devastating consequence of hyponatraemia treatment, despite cautious sodium correction.