Endocrine Abstracts

A 55-year-old lady presented with visual deterioration of 2 years duration affecting both eyes. Initial examination demonstrated reduced visual acuity in the LE at finger perception and RE 6/9 with right temporal superior quadrantopia. Rest of the systemic examination was unremarkable. Relevant endocrine tests revealed a FSH-146.9 U/l and FT₄-14 pmol/l. MRI pituitary demonstrated a pituitary adenoma with significant suprasellar component compressing the optic nerves. She underwent craniotomy with debulking of adenoma. On post op day 2 she started vomiting, serum Na was 132 mmol/l and urine output (UO) 4 l/24 h. A provisional diagnosis of DI was made and DDAVP 1 mcg was administered. Post op day 5- Na dropped to 126 mmol/l, with clinical euvolaemia, which raised the possibility of SIADH, and she was fluid restricted to <1 l/24 h. Post op day 6, Na dropped further to 116 mmol/l, she became dysphasic, drowsy and mildly dehydrated. Urinary Na was 151 mmol/l and UO was 3300 ml in previous 24 h. A diagnosis of cerebral salt wasting syndrome (CSWS) was made, CVP was low and she was treated initially with N saline and then twice N saline. This led to gradual improvement in serum Na, reaching near normal levels on post op day 11, and progressive improvement in neurology with normalisation of speech. Post-op MRI pituitary revealed a residual tumour and histology was diagnostic of FSHoma. At 3 months clinic visit, she had a normal water deprivation test, adequate adrenal reserve and remained on replacement thyroxine.

SIADH and CSWS can both present following pituitary surgery with low serum Na and osmolarity, and inappropriately elevated urine osmolarity and urine Na >40 mEq/l. CSWS is characterised by hypovolaemic hyponatremia with a marked natriuresis, whilst SIADH occurs in the setting of euvolemia and antidiuresis. Distinguishing the two can sometimes present a challenge, particularly when signs of hypovolaemia are subtle. A continued fall in serum sodium despite negative fluid balance and a high urine output suggests CSWS rather than SIADH. Making the correct diagnosis is imperative, since fluid restriction in CSWS can potentially worsen hyponatraemia and volume depletion.