Endocrine Abstracts

Background: The insulin tolerance test (ITT) is widely regarded as the gold standard for assessing central adrenal insufficiency in patients undergoing pituitary surgery. However, due to its higher cost, time burden, and potential risks such as hypoglycaemia, the short Synacthen test (SST) is often used instead. While convenient, SST may have limitations in the peri-operative period, particularly early after surgery when the hypothalamic–pituitary–adrenal (HPA) axis may be suppressed. We present a case illustrating the risk of relying solely on SST, leading to missed adrenal insufficiency.

Case Presentation: A 23-year-old woman presented with headaches and secondary amenorrhoea. She had no significant past medical history, had never used exogenous steroids, and was not on any regular medications. Initial pituitary MRI demonstrated a 2.7 cm macroadenoma without optic chiasmal compression or cavernous sinus invasion; a repeat MRI at six months showed interval growth to 3.1 cm. Visual fields were normal to confrontation, and she exhibited no features of Cushing’s syndrome or acromegaly. Baseline biochemistry showed hypogonadotropic hypogonadism (FSH 2.1 IU/l, LH 1.6 IU/l, oestradiol 54 pmol/l), normal prolactin, IGF-1 26 nmol/l, TSH 2.3 mU/l, FT4 11 pmol/l, and 9 am cortisol 465 nmol/l. She underwent elective transsphenoidal surgery. On postoperative day two, cortisol was borderline at 187 nmol/l; hydrocortisone replacement was commenced with plans for reassessment. At six weeks, SST showed an apparently adequate cortisol response (peak 490 nmol/l at 60 minutes), and hydrocortisone was discontinued. Subsequently, she developed progressive symptoms of adrenal insufficiency including dizziness, nausea, vomiting, and unintentional weight loss. Repeat SST again showed a “normal” peak cortisol, creating diagnostic uncertainty. A therapeutic trial of hydrocortisone led to marked symptomatic improvement. Although ITT was not performed in this case, it remains the reference standard for evaluating central adrenal function and would likely have clarified the diagnosis earlier.

Discussion: This case highlights that SST performed early after pituitary surgery may yield falsely reassuring results. The adrenal glands can respond adequately to Synacthen even when ACTH secretion is impaired, leading to under-recognition of central adrenal insufficiency. Persistent symptoms should prompt reassessment and, in equivocal cases, dynamic testing with ITT where feasible.

Conclusion: SST results should be interpreted cautiously in the early postoperative period after TSS. Clinical judgement remains essential, and ITT continues to have an important role when there is diagnostic uncertainty. Early recognition and treatment of adrenal insufficiency can significantly reduce morbidity.