Since a medical history indicating that the patient had suffered from a neoplasm often precedes the development of ectopic ACTH syndrome, diagnosis of the latter condition is not very difficult. If, however, the ectopic ACTH syndrome is due to an endocrine tumour, especially in the case of a carcinoid tumour, it sometimes precedes the discovery of the neoplasm. The diagnosis of this syndrome is confirmed by the following observations: elevation of plasma ACTH and cortisol levels and urinary free cortisol excretion; and failure to suppress plasma cortisol and urinary free cortisol after high-dose dexamethasone administration (8mg/d for two days).
