Endocrine Abstracts

Evaluation of the hypothalamic-pituitary-adrenal (HPA) axis using the short Synacthen test (SST) should only be performed during stable disease. Results correlate with insulin tolerance tests, provided the patient has not recently undergone surgery. In ACTH-dependent Cushings, adrenal hyperplasia occurs due to chronic ACTH stimulation. Following surgical removal of the ACTH source, only morning cortisol levels are reliable. A successful outcome in ACTH-dependent Cushings is indicated by undetectable cortisol levels, confirming the removal of the ACTH source. SST is not performed post-surgery as adrenal hyperplasia may cause a strong response to ACTH, even in the absence of endogenous ACTH. Glucocorticoid replacement is essential postoperatively, as suppressed corticotrophs require months to recover. We present a case of Cushing’s syndrome due to ectopic ACTH production from a lung carcinoid tumor. Unlike the expected prolonged adrenal hyperplasia, this case demonstrated rapid adrenal atrophy postoperatively.

Case: A 36-year-old Saudi woman exhibited Cushingoid features for three years. ONDST was 488 nmol/L, and ACTH was 81.8 ng/L. Inferior petrosal sinus sampling (IPSS) with desmopressin confirmed ectopic ACTH production. Gallium-68-DOTATATE PET identified a gallium-avid lesion in the left lung.

Management: A 14 mm lesion was excised (13/03/2024) and confirmed as an atypical carcinoid (pT1b, N0, Mx). Postoperatively, cortisol levels were undetectable, and the patient was started on prednisolone (8 mg/day). Surprisingly, an SST at 8 weeks revealed undetectable cortisol levels even at 60 minutes, suggesting complete adrenal atrophy. By 6 months, cortisol levels remained suboptimal during a short Synacthen test (SST), with results of 29 nmol/L at 0 minutes, 108 nmol/L at 30 minutes, and 147 nmol/L at 60 minutes before prednisolone 3mg. The patient remains on low-dose prednisolone, with gradual weaning under supervision. Adrenal atrophy following ACTH source removal is rapid, and synacthen tests may be useful 8 weeks after surgery.