Isolated second-phase diabetes insipidus post-transsphenoidal surgery.

A 57-year-old woman presented with severe lethargy, dizziness and nausea 1 week after transsphenoidal resection of a growth hormone secreting pituitary adenoma. She was found to have severe hyponatremia of 115 mmol/L. Importantly, she was neurologically intact and clinically euvolaemic. Her fluid intake was restricted and her sodium levels increased to 131 mmol/L over 4 days. She made a full recovery.She was diagnosed with isolated second-phase diabetes insipidus, a state of symptomatic hypoosmolar hyponatremia that usually occurs 7-10 days after transsphenoidal surgery. The sodium levels improve with fluid restriction.