Endocrine Abstracts

80-year-old female admitted with a fractured neck of femur was found to have hypernatraemia refractory to treatment. On initial assessment, she was polydipsic and hypovolaemic. She had a background of chronic kidney disease. During admission, her serum sodium rose to 167 mmol/l, eGFR was stable at 69 mL/min and her calcium and potassium were within normal limits. Her HbA1c was 40 mmol/mol excluding diabetes mellitus. On further assessment, she reported polyuria (up to 7L/day) in the months preceding her admission. Osmolality testing revealed a raised serum osmolality 317 mmol/kg with a reduced urine osmolality 137 mmol/kg. A water deprivation test was performed with partial response. Her urine osmolality increased from 106 mmol/kg to 372 mmol/kg following the administration of Desmopressin. There was no history of head injury. Her pituitary profile, vasculitis screen and MRI head were normal. She was managed for partial cranial diabetes insipidus and started on Desmopressin 100 mg once daily. This led to a significant decline in her serum sodium over the next few days (159 mmol/l to 136 mmol/l) and Desmopressin was held. Her serum sodium subsequently increased, rising to 160 mmol/l. She was restarted on Desmopressin, and eventually stabilised on a very low dose of 50 mg on alternative days. She remains well at follow up. This case describes an insidious presentation of partial cranial diabetes insipidus of unknown aetiology in a patient presenting with a fall and hypernatraemia. Careful assessment achieved clinical and biochemical improvement with a very low dose of Desmopressin. Hypernatraemia is not an uncommon presentation in the elderly and diabetes insipidus should be considered as a differential diagnosis, particularly in those refractory to conventional treatment.