Endocrine Abstracts

A 54-year-old man with a recurrent non-functioning pituitary gonadotroph adenoma previously treated with transphenoidal surgery (TSS) in 2015, presented to Charing Cross hospital for repeat transsphenoidal surgery in May 2022. Since his initial surgery, he remained on Levothyroxine 50 μg once daily only. There was no evidence of adrenal insufficiency (0900 h cortisol 333 nmol/l at day 6 following initial TSS). In February 2022, his electrolytes, FSH, LH, testosterone, prolactin and IGF-1 levels were normal. A repeat Short Synacthen Test (SST) showed normal results (baseline cortisol 94 nmol/l, 30 minutes 404 nmol/l, 60 minutes 451 nmol/l). Routine pre-operative bloods on the day of admission for repeat surgery in May 2022 showed a new hyponatraemia of 125 mmol/l (range 133–145 mmol/l) and an undetectable cortisol (<28 nmol/l). He was given an induction dose of Hydrocortisone pre-operatively, and immediately became polyuric passing over 200 ml per hour, with a total of 6050 ml in 24 h. His operation was postponed and the polyuria settled within 24 h. Repeat bloods the following morning showed a sodium of 133 mmol/l. He was discharged on replacement Prednisolone 4 mg once daily, and a repeat TSS was rearranged. The ACTH deficiency prevented free water clearance, which immediately reversed on treatment with Hydrocortisone. The ACTH deficiency was presumed to be a result of corticotroph suppression by tumour growth against the sella turcica. A subsequent water deprivation test on replacement Prednisolone, to ensure that the glucocorticoid replacement had not uncovered vasopressin deficiency, was entirely normal. He subsequently had TSS in June 2022. A postoperative SST revealed a baseline cortisol of 283 nmol/l, 30 min 517 nmol/l and 60 min 631 nmol/l. His Prednisolone was hence weaned down to 3 mg and then stopped. His TSH also normalized, and the Levothyroxine was stopped. Textbook definitions for syndrome of inappropriate antidiuretic hormone secretion (SIADH) state that patients must have adequate cortisol and thyroxine reserve to make the diagnosis. This case, however, confirms that deficiency of either, can present as SIADH, which resolves when these hormones are replaced. Our case also highlights that corticotrophs are sensitive to the pressure effects of pituitary tumours, but that full recovery can occur following surgical decompression. It is important that patients’ hypothalamic–pituitary–adrenal axis are reassessed to avoid unnecessary glucocorticoid replacement.