A case of persistent hyponatraemia due to reset osmostat.

We report a case of a 65 year old Malay lady with long-standing diabetes mellitus, who presented to our institution with a one month history of worsening neck pain and progressive upper and lower limb weakness. She was stable despite severe hyponatraemia which was initially treated as syndrome of inappropriate anti-diuretic hormone (SIADH). This was consistent with her underlying illness which was concluded as cervical tuberculosis (TB) with spinal cord compression. She underwent decompression and bone grafting. Despite continuous treatment her serum sodium levels remained low. There were no other problems with her adrenals or thyroid. A water loading and hypertonic saline perfusion test was performed and supported the diagnosis of reset osmostat. Her serum sodium remained below the normal range and she was discharged well.