Endocrine Abstracts

A 31 year old man with a 12 month history of uncontrolled hypertension was referred for further investigation. He complained of easy bruising, muscle weakness and severe back and hip pains. Clinical signs included cushingnoid facies, centripetal obesity, atrophic skin, peripheral oedema and BP of 150/104. Initial investigations confirmed Cushing's syndrome with 24 hour urinary free cortisol 696 nanomols per litre and 9am plasma cortisol 658 nanomols per litre following midnight dexamethasone 1mg. Plasma ACTH also failed to suppress with 2mg dexamethasone for 48 hours. Cortisol increased by 10 percent in response to CRH.
Although the biochemical tests appeared to suggest an ectopic source for ACTH, a 6 millimetre adenoma was evident on MR scanning of the pituitary. Inferior petrosal sinus (IPS) sampling was therefore performed. The IPS/peripheral ratio was 1.1 pre-CRH and 1.3 post-CRH with confirmed correct siting of cannulae. CT scanning of the abdomen identified normal adrenals. Octreotide scanning was negative.
After much debate regarding differential diagnoses and management, trans-sphenoidal selective adenectomy was undertaken. Immunocytochemical staining of the resected tissue was strongly positive for ACTH. Post-operatively, cortisol levels remained elevated and a 24 hour urinary free cortisol was 814 nanomols per litre. The patient has since undergone bilateral adrenalectomy. A repeat octreotide scan has not identified any ectopic ACTH source post-operatively. CT pituitary showed no evidence of residual adenoma.
This case highlights the importance of petrosal sinus sampling in ACTH dependent Cushing's syndrome even in the presence of an obvious pituitary adenoma. Exclusion of incidental non-functioning pituitary adenoma in ectopic ACTH induced Cushing's syndrome is an important pitfall to be aware of in the management of this condition.