Endocrine Abstracts

Background: Mild autonomous cortisol secretion (MACS) is most frequently associated with adrenal incidentalomas and is seldom considered in the context of pituitary incidentalomas. Patients with overt Cushing’s syndrome are well recognised to develop steroid withdrawal symptoms following curative surgery; however, the timing and recognition of such symptoms in MACS are less well established. We report a case of a missed MACS diagnosis in a pituitary incidentaloma presenting with delayed onset steroid withdrawal symptoms after transsphenoidal surgery (TSS).

Case Presentation: A 34-year-old woman was referred to endocrinology with irregular menses, headaches, and right-sided visual field impairment. She reported recent weight gain but lacked overt cushingoid or acromegalic features. Imaging demonstrated a pituitary macroadenoma compressing the right optic chiasm. Baseline investigations revealed hypogonadotropic hypogonadism (FSH 1.1 IU/l, LH 1 IU/l, oestradiol 97 pmol/l), mild hyperprolactinaemia (650 mIU/l), and secondary hypothyroidism (TSH 1.3 mU/l, FT4 7.3 pmol/l). Morning cortisol was 588 nmol/l; ACTH was insufficient for interpretation, and an overnight dexamethasone suppression test (ODST) was not performed. IGF-1 was normal. She commenced levothyroxine and underwent TSS two weeks later. Initial postoperative recovery was excellent with rapid improvement in energy and functional status. However, four weeks postoperatively she developed progressive fatigue, dizziness, poor appetite, and unintentional weight loss. Postoperative short Synacthen testing (SST) was normal on two occasions, although SST is recognised to have limited specificity in this context. Due to worsening symptoms, a trial of hydrocortisone was initiated with marked clinical improvement. Unexpectedly, histopathology confirmed a corticotroph adenoma. Subsequent ACTH and 24-hour urinary free cortisol were normal.

Discussion: This case illustrates that MACS can occur in pituitary incidentalomas and may be missed if routine preoperative screening for cortisol excess is not undertaken. Importantly, steroid withdrawal symptoms can present later than classically expected and may occur despite apparently normal postoperative dynamic adrenal testing. Histopathology remains essential when biochemical results are inconclusive.

Conclusion: Cortisol excess should be thoroughly excluded in all patients with pituitary masses, even in the absence of classic cushingoid features. Preoperative screening with ODST or equivalent is critical for surgical planning, patient counselling, and postoperative care. Early recognition of subtle cortisol excess may prevent significant morbidity related to delayed steroid withdrawal syndromes.