Syndrome of inappropriate antidiuretic hormone secretion in a patient with pituitary apoplexy.

Pituitary apoplexy (PA) is an endocrine emergency presenting with headache, visual and hormonal disturbances. Syndrome of inappropriate antidiuretic hormone secretion (SIADH) is rare after PA. A 64-year-old woman presented with acute frontal headache and nausea with normal neurological examination. Labs included normal sodium and creatinine. Echo showed new-onset congestive heart failure (CHF) and MRI of the brain revealed PA. She had normal cortisol levels and low thyroid stimulating hormone with normal thyroxine (T4) levels. During her hospitalisation, patient developed hyponatraemia. Initially, this was attributed to CHF and she was treated with tolvaptan with normalisation of sodium. One week later, she was readmitted with diarrhoea and hyponatraemia. She was euvolaemic on examination indicating compensated CHF. Despite fluid challenge, patient had no improvement of sodium levels. The diagnosis of SIADH was made. Clinicians should suspect SIADH in patients with hyponatraemia in the setting of PA with normal T4 and cortisol levels.