This clinical situation is frequently referred to as 'occult' ectopic ACTH syndrome. The reason behind this might be the indolent course of carcinoids and as reported in 44 per cent of patients, the neoplasm was initially occult (3).
Biochemically, ectopic ACTH syndrome is frequently associated with exceedingly high circulating concentrations of corticotropin (23), as seen in our patients.
However, incidental adenomas of the pituitary gland are present in up to 35 per cent of adults (27), thus that hypophysectomy occasionally yields a nonfunctioning pituitary adenoma in patients with ectopic ACTH syndrome, is not surprising.
In conclusion, ectopic ACTH syndrome due to slowly growing tumours like carcinoids usually presents with clinical features indistinguishable from classical Cushing's.